NORECS / Support / References Search FAQ Order and Enquiry Contact Language
Published references

These publications have a reference to ProboStat™ or other NorECs products

All   1-25   26-50   51-75   76-100   101-125   126-150   151-175   176-200   201-225   226-250   251-275   276-300   301-325   326-350   351-375   376-400   401-425   426-450   451-  

Computational Prediction and Experimental Realization of p-Type Carriers in the Wide-Band-Gap Oxide SrZn1–xLixO2

Authors Christos A. Tzitzeklis, Jyoti K. Gupta, Matthew S. Dyer, Troy D. Manning, Michael J. Pitcher, Hongjun J. Niu, Stanislav Savvin, Jonathan Alaria, George R. Darling, John B. Claridge, and Matthew J. Rosseinsky
Source
Inorg. Chem.
Time of Publication: 2018
Abstract It is challenging to achieve p-type doping of zinc oxides (ZnO), which are of interest as transparent conductors in optoelectronics. A ZnO-related ternary compound, SrZnO2, was investigated as a potential host for p-type conductivity. First-principles investigations were used to select from a range of candidate dopants the substitution of Li+ for Zn2+ as a stable, potentially p-type, doping mechanism in SrZnO2. Subsequently, single-phase bulk samples of a new p-type-doped oxide, SrZn1–xLixO2 (0 < x < 0.06), were prepared. The structural, compositional, and physical properties of both the parent SrZnO2 and SrZn1–xLixO2 were experimentally verified. The band gap of SrZnO2 was calculated using HSE06 at 3.80 eV and experimentally measured at 4.27 eV, which confirmed the optical transparency of the material. Powder X-ray diffraction and inductively coupled plasma analysis were combined to show that single-phase ceramic samples can be accessed in the compositional range x < 0.06. A positive Seebeck coefficient of 353(4) μV K–1 for SrZn1–xLixO2, where x = 0.021, confirmed that the compound is a p-type conductor, which is consistent with the pO2 dependence of the electrical conductivity observed in all SrZn1–xLixO2 samples. The conductivity of SrZn1–xLixO2 is up to 15 times greater than that of undoped SrZnO2 (for x = 0.028 σ = 2.53 μS cm–1 at 600 C and 1 atm of O2).
Remark DOI: 10.1021/acs.inorgchem.8b00697
Link

Thermoelectric Properties of (1-x)LaCoO3.(x)La0.95Sr0.05CoO3 composite

Authors Ashutosh Kumar, Karuna Kumari, B Jayachandran, D Sivaprahasam and Ajay D Thakur
Source
Materials Research Express
Time of Publication: 2018
Abstract Thermopower in cobalt oxides has been a rich area of interest due to the existence of the different charge states along-with different spin states. In this report, we have systematically studied the structural and thermal transport properties of ($1-x$)LaCoO$_3$.($x$)La$_{0.95}$Sr$_{0.05}$CoO$_3$ composite. The Seebeck coefficient ($alpha$) values for the composite increases at high temperatures compared to the LaCoO$_3$ (LCO) and La$_{0.95}$Sr$_{0.05}$CoO$_3$ (LSCO) systems. The electrical conductivity ($sigma$) decreases with the increase in the LSCO fraction which may be attributed to the localization of charge carriers due to intersite diffusion. All the samples show increase in the value of $sigma$ with increase in temperature. The thermal conductivity ($kappa$) values decrease with the increase of LSCO content in the composite and the phonon thermal conductivity dominates over the total thermal conductivity. We observe a maximum value of figure of merit (ZT)$sim$0.06 at 640,K for $x=$0.05.
Remark Link

Wide bandgap oxides for low-temperature single-layered nanocomposite fuel cell

Authors Muhammad Imran Asghar, Sami Jouttijrvi, Riina Jokiranta, Anna-Maija Valtavirta, Peter D. Lund
Source
Nano Energy
Volume: 53, Pages: 391-397
Time of Publication: 2018
Abstract A composite of wide bandgap lithium-nickel-zinc-oxide (LNZ) and gadolinium-doped-cerium-oxide (GDC) was systematically analyzed for a low-temperature nanocomposite fuel cell in a so-called single-component configuration in which the electrodes and electrolyte form a homogenous mixture. We found that the operational principle of a single-layer fuel cell can be explained by electronic blocking by the oxide mixture with almost insulator-like properties in the operating voltage regime of the fuel cell, which will prevent short-circuiting, and by its catalytic properties that drive the fuel cell HOR and ORR reactions. The resistance to charge transport and leakage currents are dominant performance limiting factors of the single-component fuel cell. A test cell with Au as current collector reached a power density of 357 mWcm−2 at 550 C. Changing the current collector to a Ni0.8Co0.15Al0.05LiO2 (NCAL) coated Ni foam produced 801 mWcm−2, explained by better catalytic properties. However, utilizing NCAL coated Ni foam may actually turn the 1-layer fuel cell device into a traditional 3-layer (anode-electrolyte-cathode) structure. This work will help in improving the understanding of the underlying mechanisms of a single-layer fuel cell device important to further develop this potential energy technology.
Keywords Bandgap; Ceramic; Fuel cell; Ionic conductivity; Nanocomposite; Single-component
Remark https://doi.org/10.1016/j.nanoen.2018.08.070
Link

Crystal Structure and Coordination of B-Cations in the Ruddlesden–Popper Phases Sr3−xPrx(Fe1.25Ni0.75)O7−δ (0 ≤ x ≤ 0.4)

Authors Gunnar Svensson, Louise Samain, Jordi Jacas Biendicho, Abdelfattah Mahmoud, Raphal P. Hermann, Sergey Ya. Istomin and Jekabs Grins
Source
Inorganics
Volume: 6, Issue: 3 Time of Publication: 2018
Abstract Compounds Sr3−xPrxFe1.25Ni0.75O7−δ with 0 ≤ x ≤ 0.4 and Ruddlesden–Popper n = 2 type structures were synthesized and investigated by X-ray and neutron powder diffraction, thermogravimetry, and Mssbauer spectroscopy. Both samples, prepared at 1300 C under N2(g) flow and samples subsequently air-annealed at 900 C, were studied. The structures contained oxygen vacancies in the perovskite layers, and the Fe/Ni cations had an average coordination number less than six. The oxygen content was considerably higher for air-annealed samples than for samples prepared under N2, 7 − δ = ~6.6 and ~5.6 per formula unit, respectively. Mssbauer data collected at 7 K, below magnetic ordering temperatures, were consistent with X-ray powder diffraction (XRD) and neutron powder diffraction (NPD) results. The electrical conductivity was considerably higher for the air-annealed samples and was for x = 0.1~30 Scm−1 at 500 C. The thermal expansion coefficients were measured in air between room temperature and 900 C and was found to be 20–24 ppmK−1 overall.
Keywords Ruddlesden–Popper structure; oxygen non-stoichiometry; crystal structure; Mssbauer spectroscopy; electrical conductivity; thermal expansion
Remark Link

All-Oxide Thermoelectric Module with in Situ Formed Non-Rectifying Complex p–p–n Junction and Transverse Thermoelectric Effect

Authors Nikola Kanas, Michael Bittner, Temesgen Debelo Desissa, Sathya Prakash Singh, Truls Norby, Armin Feldhoff, Tor Grande, Kjell Wiik, and Mari-Ann Einarsrud
Source
ACS Omega
Volume: 3, Issue: 8, Pages: 9899–9906
Time of Publication: 2018
Abstract All-oxide thermoelectric modules for energy harvesting are attractive because of high-temperature stability, low cost, and the potential to use nonscarce and nontoxic elements. Thermoelectric modules are mostly fabricated in the conventional π-design, associated with the challenge of unstable metallic interconnects at high temperature. Here, we report on a novel approach for fabrication of a thermoelectric module with an in situ formed p–p–n junction made of state-of-the-art oxides Ca3Co4–xO9+δ (p-type) and CaMnO3–CaMn2O4 composite (n-type). The module was fabricated by spark plasma co-sintering of p- and n-type powders partly separated by insulating LaAlO3. Where the n- and p-type materials originally were in contact, a layer of p-type Ca3CoMnO6 was formed in situ. The hence formed p–p–n junction exhibited Ohmic behavior and a transverse thermoelectric effect, boosting the open-circuit voltage of the module. The performance of the module was characterized at 700–900 C, with the highest power output of 5.7 mW (around 23 mW/cm2) at 900 C and a temperature difference of 160 K. The thermoelectric properties of the p- and n-type materials were measured in the temperature range 100–900 C, where the highest zT of 0.39 and 0.05 were obtained at 700 and 800 C, respectively, for Ca3Co4–xO9+δ and the CaMnO3–CaMn2O4 composite.
Remark DOI: 10.1021/acsomega.8b01357

An operando calorimeter for high temperature electrochemical cells

Authors David Young, Ariel Jackson, David Fork, Seid Sadat, Daniel Rettenwander, Jesse D. Benck, Yet - Ming Chiang
Source
Time of Publication: 2018
Abstract Operando calorimetry has previously been utilized to study degradation, side reactions, and other electrochemical effects in electrochemical cells such as batteries at or near room temperature. Calorimetric data can provide important information on the lifetime and thermal properties of electrochemical cells and can be used in practical engineering applications such as thermal anagement. High temperature electrochemical cells such as solid oxide fuel cells or electrolyzers can also benefit from operando calorimetry, although to our knowledge no such unit has been eveloped commercially. Herein, we report an operando calorimeter capable of simultaneous calorimetry and electrochemistry at temperatures up to 1,000 C and in both oxidizing and reducing atmospheres. The calorimeter is constructed by modifying a commercial apparatus originally designed to study high temperature electrochemical cells in various gas environments. We utilize a grey - box, nonlinear system identification model to analyze calorimetric data and achieve an electrochemical cell power sensitivity of 16.111.7 mW. This operando calorimeter provides the tools needed to study both the thermal and kinetic behavior of electrochemical cells at elevated temperatures.
Remark Link

Ohmically heated ceramic asymmetric tubular membranes for gas separation

Authors Ragnhild Hancke, Thorbjrn V. Larsen, Wen Xing, Zuoan Li, Marie-Laure Fontaine, Truls Norby
Source
Journal of Membrane Science
Volume: 564, Pages: 598-604
Time of Publication: 2018
Abstract Mixed conducting dense ceramic gas separation membranes can be used in air separation for oxy-fuel and pre-combustion processes in CO2 capture schemes for emission-free power plants and chemical industries. Such membranes operate at high temperatures, and the energy penalty associated with heating the membranes with external electrical heaters or burners via the feed or sweep gas can be significantly reduced by adopting direct ohmic heating of the membrane. We demonstrate that tubular asymmetric gas separation membranes of La2NiO4+δ and La0.87Sr0.13CrO3-δ can be heated to temperatures in excess of 800 C by passing current through them, and that such ohmically heated tubular membranes can be operated in an oxygen potential gradient to selectively separate oxygen from a feed gas mixture. We highlight the associated challenges with heat transport and thermal gradients and undertake numerical simulations to investigate the effect of materials properties on heating power and heat distribution in the tubes.
Keywords Membranes, ceramic, dense; Gas separation; Ohmic heating, La2NiO4; LaCrO3
Remark https://doi.org/10.1016/j.memsci.2018.07.070
Link

A novel anode for solid oxide fuel cells prepared from phase conversion of La0.3Sr0.7Fe0.7Cr0.3O3-δ perovskite under humid hydrogen

Authors Min Chen, Yang Hu, Dongchu Chen, Huawen Hu, Qing Xu
Source
Electrochimica Acta
Volume: 284, Pages: 303-313
Time of Publication: 2018
Abstract A novel anode for solid oxide fuel cells (SOFCs), consisting of a Ruddlesden-Popper compound, La0.6Sr1.4Fe0.4Cr0.6O3.8, with in situ exsolved α-Fe nanoparticles (RP-LSF + Fe), is prepared from the phase conversion of the La0.3Sr0.7Fe0.7Cr0.3O3-δ (LSFCr-3) perovskite under humid H2 at 800 C. On the surface of the RP-LSF + Fe anode, Fe cations are presented to be a mixture of Fe2+ and Fe3+, of which the average valence is lower than that in the bulk (Fe3+). The coverage of atomic hydrogen on the RP-LSF + Fe anode is over 0.8 in the pH2 range of 0.017–0.27 atm, implying a significant effect of these small amount (∼8 mol% on the surface) of exsolved Fe nanoparticles (∼200–300 nm) on promoting the dissociative absorption of H2. The charge transfer resistance is found to be closely related to the concentration of surface oxygen vacancies of the oxide matrix. The addition of catalytic amount of Ni (1–3 wt.%) greatly improves the fuel flexibility of the RP-LSF + Fe anode. Furthermore, it contributes to acceleration the phase conversion of the LSFCr-3 perovskite and reduced time for in situ preparation of the RP-LSF + Fe anode. The RP-LSF + Fe anode with 2.7 wt.% Ni exhibits a stable cell performance under 2.7%H2O+1:1-(H2:CO) and 2.7%H2O + CH4 for ∼30 h. It costs shortest time (30 h) to reach a stable cell voltage of 0.76 V at a galvanostatic current density of 0.25 A/cm2 under humid H2, which is clearly an active and stable anode material for SOFCs.
Keywords Solid oxide fuel cell, Oxide anode, Phase conversion, Electrodics, Fuel flexibility
Remark https://doi.org/10.1016/j.electacta.2018.07.132
Link

Assessment of layered La2-x(Sr,Ba)xCuO4-δ oxides as potential cathode materials for SOFCs

Authors Anna Niemczyk, Anna Olszewska, Zhihong Du, Zijia Zhang, Konrad Świerczeka, Hailei Zhao
Source
International Journal of Hydrogen Energy
Volume: 43, Issue: 32, Pages: 15492-15504
Time of Publication: 2018
Abstract In this paper, selected layered cuprates with La2-x(Sr,Ba)xCuO4-δ formula are evaluated as candidate cathode materials for Solid Oxide Fuel Cells. Two synthesis routes, a typical solid state reaction and a sol-gel method yield well-crystallized La1.5Sr0.5CuO4-δ, La1.6Ba0.4CuO4-δ and La1.5Sr0.3Ba0.2CuO4-δ materials having tetragonal I4/mmm space group, but differing in morphology of the powder. Fine powders obtained using sol-gel route seem to be more suitable for preparation of the porous cathode layers having good adhesion on the solid electrolyte, but powders obtained after the solid state route can be also successfully utilized. Investigations of structural and transport properties, the oxygen nonstoichiometry and its change with temperature, thermal expansion, as well as chemical and thermal stability are systematically performed, to evaluate and compare basic physicochemical properties of the oxides. At room temperature the average valence state of copper is found to be in 2.2–2.35 range, indicating oxygen deficiency in all of the compounds, which further increases with temperature. The conducted high-temperature X-ray diffraction tests reveal moderate, but anisotropic thermal expansion of La2-x(Sr,Ba)xCuO4-δ, with higher expansion at temperatures above 400 C occurring along a-axis, due to the oxygen release. However, the corresponding chemical expansion effect is small and the materials possess moderate thermal expansion in the whole studied temperature range. All compounds show relatively high electrical conductivity at the elevated temperatures, related to the Cu2+/Cu3+ charge transfer, with the highest values recorded for La1.5Sr0.5CuO4-δ. Comprehensive studies of chemical stability of the selected La1.5Sr0.5CuO4-δ material with La0.8Sr0.2Ga0.8Mg0.2O3-δ solid electrolyte revealed complex behavior, with stability being dependent apart from temperature, also on morphology of the powders. A model describing such behavior is presented. While it is possible to minimize reactivity and characterize electrochemical properties of the La1.5Sr0.5CuO4-δ-based cathode layer, usage of the buffer layer is indispensable to maintain full stability. It is shown that mutual chemical compatibility of La1.5Sr0.5CuO4-δ and commonly used La0.4Ce0.6O2-δ buffer layer material is excellent, with no reactivity even at 1000 C for prolonged time. Laboratory-scale fuel cell with the La1.5Sr0.5CuO4-δ cathode sintered at the optimized temperature is able to deliver 0.16 W cm−2 at 800 C while fueled with wet hydrogen.
Keywords Layered cuprates, Cathodic polarization, Chemical stability, LSGM, Buffer layer, SOFC
Remark https://doi.org/10.1016/j.ijhydene.2018.06.119
Link

Sol-gel Zn, Fe modified SnO2 powders for CO sensors and magnetic applications

Authors Izabella Dascalu, Simona Somacescu, Cristian Hornoiu, Jose M. Calderon-Moreno, Nicolae Stanica, Hermine Stroescu, Mihai Anastasescu, Mariuca Gartner
Source
Process Safety and Environmental Protection
Volume: 117, Pages: 722-729
Time of Publication: 2018
Abstract Zn, Fe modified SnO2 powders were prepared by sol-gel method using Tripropylamine as chelating agent and Polyvinylpyrrolidone K90 as dispersant and stabilizer. Two compositions were taken into account: Zn, Fe modified SnO2 – 20 mol% Zn, 10 mol% Fe and Zn, Fe modified SnO2 – 20 mol% Zn, 30 mol% Fe, denoted further as SZFe1and SZFe2 respectively. The properties and the influence of Fe amount on structure, morphology and surface chemistry, electrical and magnetic properties have been investigated. The X-ray diffraction analysis showed the formation of a polycrystalline mixture of cassiterite – SnO2, hematite – Fe2O3, franklinite – ZnFe2O4 and zincite – ZnO for the samples with different Fe content. The magnetization of SZFe2 sample was found to be composed of a ferromagnetic and a paramagnetic phase. The presence of Fe in the powders composition improved the electrical properties, demonstrating performant features in sensing characteristics (tested in CO gas concentrations varied from 50 to 1000 ppm). The magnetic investigations suggest their possible future applications as soft magnetic materials.
Keywords Oxides, Sol-gel chemistry, Surface properties, Electrical properties, CO gas sensor
Remark https://doi.org/10.1016/j.psep.2018.06.010
Link

Optimization and Electrochemical Properties of Double Perovskite NdBaCo2O6–δ LaBaCo2O5+δ as Cathode Material for Solid Oxide Fuel Cell

Authors Jia, Zhenyuan; Wang, Peida; Zhong, Yuhan; Mei, Huayue
Source
Journal of Nanoelectronics and Optoelectronics
Volume: 13, Issue: 5, Pages: 749-757(9)
Time of Publication: 2018
Abstract In this paper, the double perovskite structure NdBaCo2O6–δ LaBaCo2O5+δ was used as cathode material for solid oxide fuel cell (SOFC). The cathode material was prepared using sol in situ composite method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and electrochemical measurements systems. The NdBaCo2O6–δ and (Ce, Gd, O) were prepared to get NdBaCo2O6–δ –xCe0.8Gd0.1O1.75 (x = 0–10 wt%) and with the increase of the compound (Ce, Gd, O), the electrode polarization surface resistance changes. The polarization resistance at 700 C was only 0.032 Ω cm2. The output power of single battery was 0.363 W/cm2. The sol–gel method was used to replace Co with Fe and LaBaCo2–x Fe x O5+δ (x = 0.0, 0.3, 0.5, 0.8) was prepared. It was observed that under different Fe contents, the polarization resistance of the composite cathode material LaBaCo2–x Fe x O5+δ decreases first and then increases. When x = 0.3, the minimum polarization resistance can be obtained, however, with the increase of temperature, the polarization resistance of the composite cathode material further reduced.
Remark DOI: https://doi.org/10.1166/jno.2018.2320
Link

Electrochemical and degradation study of Sr0.6Na0.4SiO3-δ

Authors Kapil Sood, Jyoti Kaswan, Surinder P. Singh, Truls Norby, Suddhasatwa Basu
Source
Journal of Solid State Electrochemistry
Volume: 22, Issue: 10, Pages: 3009–3013
Time of Publication: 2018
Abstract The high ionic conductivity of Na-doped SrSiO3 (SNS) is a topic of interest due to contradictory reports on its conductivity and stability by various groups. From a recent NMR study, it is proposed that Na+ is mainly responsible for ionic conductivity in an amorphous Na2Si2O5 phase present in SNS. The present study further extends to determine experimentally the ion transport number as well as material characteristics after long time annealing at 600 C. The conductivity behavior of as-sintered and annealed nominally Sr0.6Na0.4SiO3-δ is investigated and a sharp fall (~ 2 order magnitude) of the same at 800 C is found. An XPS study is included for comprehensive understanding of conductivity and degradation behavior of SNS material. On basis of the collective results, we propose a rational description of the conduction and material degradation of SNS.
Keywords SrSiO3, Transport number, SOFC, Ionic conductivity, Protonic conductivity
Remark Link

Novel ReBaCo1.5Mn0.5O5+δ (Re: La, Pr, Nd, Sm, Gd and Y) perovskite oxide: influence of manganese doping on the crystal structure, oxygen nonstoichiometry, thermal expansion, transport properties, and application as a cathode material in solid oxide f

Authors Anna Olszewska, Zhihong Du, Konrad Świerczek, Hailei Zhao and Bogdan Dabrowski
Source
Journal of Materials Chemistry A
Issue: 6, Pages: 13271-13285
Time of Publication: 2018
Abstract In this work, a novel series of Mn-containing ReBaCo1.5Mn0.5O5+δ (Re: selected rare earth elements) perovskite-type oxides is studied, with systematic measurements of physicochemical properties being reported. Comparison with the very well-studied, parent ReBaCo2O5+δ allows determination of the role of the introduced manganese concerning modification of the crystal structure at room temperature and its evolution at high temperatures, variation of the oxygen content, thermal stability of the materials, and total electrical conductivity, as well as thermal and chemical expansion. Generally, the presence of Mn cations does not affect the tendency for A-site cation ordering, resulting in an increased unit cell volume of the compounds, as well as causing an increase of the oxygen content. Reduced thermal expansion, together with high values of electrical conductivity and suitable thermal stability, makes the compounds containing larger Re3+ cations attractive from the point of view of application as cathode materials in solid oxide fuel cells. Chemical compatibility studies reveal the sufficient stability of the considered perovskites in relation to Ce0.8Gd0.2O2−δ solid electrolyte, while unexpected, somewhat increased reactivity towards La0.8Sr0.2Ga0.8Mg0.2O3−δ and La0.4Ce0.6O2−δ is also reported. Furthermore, the electrochemical tests of the symmetric cells show strong dependence of the polarization resistance of the electrode on the synthesis and sintering temperatures. For the selected and optimized NdBaCo1.5Mn0.5O5+δ layer employed in the electrolyte-supported (LSGM) symmetric cell with a CGO buffer layer, the cathodic polarization resistance is 0.043 Ω cm2 at 900 C. A wet hydrogen-fuelled button-type cell with the NdBaCo1.5Mn0.5O5+δ-based cathode is also prepared, delivering the maximum power density exceeding 1.3 W cm−2 at 850 C.
Remark DOI: 10.1039/C8TA03479F
Link

High performance ceramic nanocomposite fuel cells utilizing LiNiCuZn-oxide anode based on slurry method

Authors M.I. Asghar, S. Jouttijrvi, P.D. Lund
Source
International Journal of Hydrogen Energy
Time of Publication: 2018
Abstract A multi-oxide material LiNiCuZn-oxide was prepared through a slurry method as an anode for ceramic nanocomposite fuel cell (CNFC). The CNFCs using this anode material, LSCF as cathode material and a composite electrolyte consisting of CaSm co-doped CeO2 and (NaLiK)2CO3 produced ∼1.03 W/cm2 at 550 C due to efficient reaction kinetics at the electrodes and high ionic transport in the nanocomposite electrolyte. The electrochemical impedance spectroscopy revealed low ionic transport losses (0.238 Ω cm2) and low polarization losses (0.124 Ω cm2) at the electrodes. The SEM measurements revealed the porous microstructures of the composite materials at electrode and the dense mixture of CaSm co-doped CeO2 and (NaLiK)2CO3. The Brunauer-Emmett-Teller (BET) analysis revealed high surface areas, 4.1 m2/g and 3.8 m2/g, of the anode and cathode respectively. This study provides a promising material for high performance CNFCs.
Keywords Ceramic, Conductivity, Fuel cell, Multi-oxide, Nanocomposite, Synthesis
Remark https://doi.org/10.1016/j.ijhydene.2018.03.232
Link

Enhanced Performance of Gadolinia-Doped Ceria Diffusion Barrier Layers Fabricated by Pulsed Laser Deposition for Large-Area Solid Oxide Fuel Cells

Authors Miguel Morales, Arianna Pesce, Aneta Slodczyk, Marc Torrell, Paolo Piccardo, Dario Montinaro, Albert Tarancn, and Alex Morata
Source
ACS Appl. Energy Mater.
Time of Publication: 2018
Abstract Diffusion barrier layers are typically introduced in solid oxide fuel cells (SOFCs) to avoid reaction between state-of-the-art cathode and electrolyte materials, La1–xSrxCo1–yFeyO3-δ and yttria-stabilized zirconia (YSZ), respectively. However, commonly used layers of gadolinia-doped ceria (CGO) introduce overpotentials that significantly reduce the cell performance. This performance decrease is mainly due to the low density achievable with traditional deposition techniques, such as screen printing, at acceptable fabrication temperatures. In this work, perfectly dense and reproducible barrier layers for state-of-the-art cells (∼80 cm2) were implemented, for the first time, using large-area pulsed laser deposition (LA-PLD). In order to minimize cation interdiffusion, the low-temperature deposited barrier layers were thermally stabilized in the range between 1100 and 1400 C. Significant enhanced performance is reported for cells stabilized at 1150 C showing excellent power densities of 1.25 Wcm–2 at 0.7 V and at a operation temperature of 750 C. Improved cells were finally included in a stack and operated in realistic conditions for 4500 h revealing low degradation rates (0.5%/1000 h) comparable to reference cells. This approach opens new perspectives in manufacturing highly reproducible and stable barrier layers for a new generation of SOFCs.
Keywords Cation diffusion at CGO/YSZ interface; diffusion barrier layer; gadolinia doped ceria (CGO); pulsed laser deposition (PLD); solid oxide fuel cells (SOFCs); SrZrO3
Remark DOI: 10.1021/acsaem.8b00039
Link

Solid oxide fuel cells incorporating doped lanthanum gallate films deposited by radio-frequency magnetron sputtering at various Ar/O2 ratios and annealing conditions

Authors Yi-Xin Liu , Sea-Fue Wang, Yung-Fu Hsu, Wan-Yun Yeh
Source
Surface and Coatings Technology
Volume: 344, Pages: 507-513
Time of Publication: 2018
Abstract In this study, we prepared solid oxide fuel cells (SOFCs) incorporating a dense La0.87Sr0.13Ga0.88Mg0.12O3−δ (LSGM) film deposited by radio-frequency (RF) magnetron sputtering on an NiO-Sm0.2Ce0.8O2−δ (NiO-SDC) anode substrate. The influences of the Ar-O2 deposition atmosphere and the subsequent annealing conditions on the characteristics of the LSGM film and on the performance of the resulting SOFCs was investigated. LSGM targets with La0.76Sr0.24Ga0.63Mg0.37O3−δ composition and a deposition atmosphere with Ar/O2 ratios ranging from 10/0 to 5/5 were used throughout the study. Owing to the amorphous nature of the as-deposited LSGM films, the film deposited in an Ar/O2 = 10/0 atm required post-annealing at 950 C for 4 h for crystallization and removal of the SrLaGa2O7 content, while the films deposited at lower Ar/O2 ratios required higher crystallization temperatures: for instance, the films deposited at Ar/O2 = 6/4 had to be annealed at 1100 C for 2 h. The anode-supported substrates were then screen-printed with a La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF)-LSGM cathode layer and fired to form SOFC cells. The single cell incorporating an LSGM film with La0.87Sr0.13Ga0.88Mg0.12O3−δ composition deposited in a pure Ar atmosphere exhibited the lowest cell resistance and thus the highest maximum power density (MPD) at all operating temperatures. The total resistance of the single cell incorporating a 4.3 μm-thick LSGM film decreased from 0.386 to 0.121 Ω cm2 as the temperature increased from 650 to 850 C, and the open circuit voltages ranged from 0.941 to 0.861 V. The maximum power density of the single cell was 0.422, 0.736, and 1.105 W cm−2 at 650, 750, and 850 C, respectively.
Keywords Solid oxide fuel cell, Sputtering, Electrolyte, Doped lanthanum gallate
Remark https://doi.org/10.1016/j.surfcoat.2018.03.073
Link

Influence of annealing at intermediate temperature on oxygen transport kinetics of Pr2NiO4+δ

Authors Saim Saher, Jia Song, Vaibhav Vibhu, Clment Nicollet, Aurlien Flura, Jean-Marc Bassat and Henny J. M. Bouwmeester
Source
J. Mater. Chem. A
Volume: 6, Pages: 8331-8339
Time of Publication: 2018
Abstract Electrical conductivity relaxation (ECR) and oxygen permeation measurements were conducted, at 750 C, to assess the long-term oxygen transport characteristics of the mixed ionic–electronic conducting Pr2NiO4+δ with a K2NiF4 structure. The results show that the apparent values for the oxygen diffusion and surface exchange coefficients extracted from the data and the associated oxygen flux increase over 120 h by 1–2 orders of magnitude. The results of post-mortem X-ray diffraction analysis of the samples show partial to virtually complete decomposition of Pr2NiO4+δ under the conditions of the experiments to Pr4Ni3O10+δ, PrNiO3−δ, Pr6O11, and traces of NiO. Pulse 18O–16O isotopic exchange (PIE) measurements confirmed fast surface exchange kinetics of the higher-order Ruddlesden–Popper phase Pr4Ni3O10+δ and Pr6O11 formed upon decomposition. Additional factors related to the microstructure, however, need to be considered to explain the observations.
Remark Link

Thermoelectric properties of (1-x)LaCoO3.xLa0.7Sr0.3MnO3 composite

Authors Ashutosh Kumar, Karuna Kumari, B. Jayachandran, D. Sivaprahasam, Ajay D.Thakur
Source
Journal of Alloys and Compounds
Volume: 749, Pages: 1092-1097
Time of Publication: 2018
Abstract We report the thermoelectric (TE) properties of (1-x)LaCoO3.xLa0.7Sr0.3MnO3 (0 < x < 0.50) composite in a temperature range 320–800 K. Addition of La0.7Sr0.3MnO3 to LaCoO3 in small amount (5 weight %) improves the overall Seebeck coefficient (α) at higher temperatures. The electrical conductivity however decreases due to a decrease in carrier concentration of the composite. The decrease in electrical conductivity of the composite at high temperature may be attributed to the insulating nature of the LSMO above room temperature. Thermal conductivity (κ) of all the samples increases with an increase in the temperature, but decreases with increasing LSMO content. We also report the local variation of Seebeck coefficient across the composite samples measured using a precision Seebeck measurement system. A maximum value of 0.09 for the figure of merit (ZT) is obtained for 0.95LaCoO3.0.05La0.7Sr0.3MnO3 at 620 K which is significantly higher than the ZT of either of LaCoO3 or La0.7Sr0.3MnO3 at 620 K. This suggests the potential for enhancement of operating temperatures of hitherto well known low temperature thermoelectric materials through suitable compositing approach.
Keywords Thermal conductivity, Electrical conductivity, Perovskites, Manganites, Cobaltate, Composite
Remark https://doi.org/10.1016/j.jallcom.2018.03.347
Link

Lanthanum doped strontium titanate - ceria anodes: deconvolution of impedance spectra and relationship with composition and microstructure

Authors Dariusz Burnat, Gunnar Nurk, Lorenz Holzer, Michal Kopecki, Andre Heel
Source
Journal of Power Sources
Volume: 385, Pages: 62-75
Time of Publication: 2018
Abstract Electrochemical performance of ceramic (Ni-free) SOFC anodes based on La0.2Sr0.7TiO3-δ (LST) and Gd0.1Ce0.9O1.95-δ (CGO) is thoroughly investigated. Microstructures and compositions are systematically varied around the percolation thresholds of both phases by modification of phase volume fractions, particle size distributions and firing temperature. Differential impedance spectroscopy was performed while varying gas composition, electrical potential and operating temperature, which allows determining four distinct electrode processes. Significant anode impedances are measured at low frequencies, which in contrast to the literature cannot be linked with gas concentration impedance. The dominant low frequency process (∼1 Hz) is attributed to the chemical capacitance. Combined EIS and microstructure investigations show that the chemical capacitance correlates inversely with the available surface area of CGO, indicating CGO surface reactions as the kinetic limitation for the dominant anode process and for the associated chemical capacitance. In anodes with a fine-grained microstructure this limitation is significantly smaller, which results in an impressive power output as high as 0.34 Wcm−2. The anodes show high redox stability by not only withstanding 30 isothermal redox cycles, but even improving the performance. Hence, compared to conventional Ni-cermet anodes the new LST-CGO material represents an interesting alternative with much improved redox-stability.
Keywords SOFC, LST, Microstructure analysis, Electrochemical impedance, Spectroscopy, Redox Anodes
Remark https://doi.org/10.1016/j.jpowsour.2018.03.024
Link

Influence of texture and grain misorientation on the ionic conduction in multilayered solid electrolytes – interface strain effects in competition with blocking grain boundaries

Authors J. Keppner, J. Schubert, M. Ziegner, B. Mogwitz, J. Janek and C. Korte
Source
Physical Chemistry Chemical Physics
Issue: 14 Time of Publication: 2018
Abstract Interface strain and its influence on the ionic transport along hetero-interfaces has gained a lot of attention over the last decade and is controversially discussed. We investigate the relaxation of mismatch induced interfacial strain as a function of the degree of orientation/texture of the columnar crystallites and assess the impact on the oxygen ion conductivity in Er2O3/YSZ multilayer systems. Results from X-ray diffraction clearly show, that the width of the strained hetero-interface region increases with an increasing degree of orientation of the crystallites. The combined impact of film texture and strain at the hetero-interfaces of the film on the ionic conductivity however is not easily deduced from these measurements. The samples with the highest degree of orientation, i.e. with only one azimuthal variant, show strong anisotropic electrical properties. In samples with a lower degree of orientation, i.e. samples with a fiber texture, anisotropic properties cannot be detected, possibly due to a geometrical averaging of the electrical properties. The expected strain induced monotonic increase of the ionic conductivity with decreasing layer thickness and thus increasing interfacial influence could only be detected for samples with a fiber texture and a considerable degree of crystallite misorientation. This leads to the important conclusion that the texture and therefore the nature of the grain boundaries and their network influence the ionic conductivity of the multilayer thin films in the same order of magnitude as the misfit induced interface strain. Thus, the potential design of strain-controlled ionic conductors requires additionally the control of the microstructure in terms of grain orientation.
Remark Link

Crystal Structure, Hydration, and Two-Fold/Single-Fold Diffusion Kinetics in Proton-Conducting Ba0.9La0.1Zr0.25Sn0.25In0.5O3−a Oxide

Authors Wojciech Skubida, Anna Niemczyk, Kun Zheng, Xin Liu and Konrad Świeczek
Source
Crystals
Volume: 8, Issue: 3, Pages: 136
Time of Publication: 2018
Abstract In this work, hydration kinetics related to the incorporation of water into proton-conducting Ba0.9La0.1Zr0.25Sn0.25In0.5O3−a perovskite-type oxide are presented, with a recorded transition on temperature from a single-fold to a two-fold behavior. This can be correlated with an appearance of the electronic hole component of the conductivity at high temperatures. The collected electrical conductivity relaxation data allowed to calculate chemical diffusion coefficient D and surface exchange reaction coefficient k, as well as respective activation energies of their changes on temperature. Presented results are supplemented with a systematic characterization of the structural properties of materials synthesized at different temperatures, amount of incorporated water after hydration in different conditions, influence of water content on the crystal structure, as well as electrical conductivity in dry, H2O- and D2O-containing air, which enabled to evaluate proton (deuterium) conductivity.
Keywords Perovskite oxides; substituted barium indate; hydration; proton conductivity; relaxation experiments; coupled/decoupled ionic transport.
Remark doi:10.3390/cryst8030136
Link

Sol-gel synthesis of ZnO/Zn2-xFexTiO4 powders: structural properties, electrical conductivity and dielectric behavior

Authors Izabella Dascalu, Cristian Hornoiu, Jose Maria Calderon-Moreno, Madalin Enache, Daniela Culita, Simona Somacescu
Source
Journal of Sol-Gel Science and Technology
Volume: 86, Issue: 1, Pages: 151–161
Time of Publication: 2018
Abstract The aim of this work was an investigation of structural and electrical properties of ZnO/Zn2-xFexTiO4 (x = 0.7, 1, 1.4) powders. The compounds obtained by sol-gel method are characterized by several techniques: X-ray diffraction (XRD), N2 adsorption–desorption isotherms, scanning and transmission electron microscopy (SEM and TEM), X-ray photoelectron spectroscopy (XPS), electrical and dielectrical measurements. The XRD, SEM and XPS analysis confirmed the formation of ZnFeTiO4 inverse spinel structure. The electrical and dielectrical properties of ZnO/Zn2-xFexTiO4 (x = 0.7, 1, 1.4) were measured by impedance spectroscopy, revealing a decrease in the electrical conductivity and the dielectric constant with Fe content.
Keywords Sol-gel, ZnO/ZnFeTiO4, dielectric constant, AC conductivity
Remark Link

p-Type/n-type behaviour and functional properties of KxNa(1-x)NbO3 (0.49 ≤ x ≤ 0.51) sintered in air and N2

Authors Fayaz Hussain, Iasmi Sterianou, Amir Khesro, Derek C. Sinclair, Ian M. Reaney
Source
Journal of the European Ceramic Society
Volume: 38, Issue: 9, Pages: 3118-3126
Time of Publication: 2018
Abstract Potassium sodium niobate (KNN) is a potential candidate to replace lead zirconate titanate in sensor and actuator applications but there are many fundamental science and materials processing issues to be understood before it can be used commercially, including the influence of composition and processing atmosphere on the conduction mechanisms and functional properties. Consequently, KNN pellets with different K/Na ratios were sintered to 95% relative density in air and N2 using a conventional mixed oxide route. Oxygen vacancies (VO••) played a major role in the semi-conduction mechanism in low p(O2) for all compositions. Impedance spectroscopy and thermo-power data confirmed KNN to be n-type in low p(O2) in contradiction to previous reports of p-type behaviour. The best piezoelectric properties were observed for air- rather than N2-sintered samples with d33 = 125 pC/N and kp = 0.38 obtained for K0.51Na0.49NbO3.
Keywords p-Type, n-Type, Low p(O2), Oxygen vacancies, Seebeck coefficient
Remark https://doi.org/10.1016/j.jeurceramsoc.2018.03.013
Link

La1.8Sr0.2Ni0.8M0.2O4 (M = Fe, Co, or Cu) Complex Oxides: Synthesis, Structural Characterization, and Dielectric Properties

Authors T.I. Chupakhina, N.V. Mel’nikova, E.A. Yakovleva, Yu. A. Nikitina
Source
Russian Journal of Inorganic Chemistry
Volume: 63, Issue: 2, Pages: 141–148
Time of Publication: 2018
Abstract New solid solutions La1.8Sr0.2Ni0.8M0.2O4 (M = Fe, Co, or Cu) have been prepared, and their crystal- chemical characteristics and electric properties studied. The studied materials have been shown to have activation-time conductivity. Structural distortions have been found to affect the dielectric properties of ceramic samples. La1.8Sr0.2Ni0.8M0.2O4 is observed to have the greatest distortion of АО9 coordination polyhedra and a higher dielectric constant.
Remark Link

Inter-diffusion across a direct p-n heterojunction of Li-doped NiO and Al-doped ZnO

Authors Temesgen D. Desissa, Reidar Haugsrud, Kjell Wiik, Truls Norby
Source
Solid State Ionics
Volume: 320, Pages: 215-220
Time of Publication: 2018
Abstract We herein report inter-diffusion across the interface between p-type Ni0.98Li0.02O and n-type Zn0.98Al0.02O for various applications including p-n-heterojunction diodes and oxide thermoelectrics. Diffusion couples were made of polished surfaces of ceramic samples pre-sintered at 1250 and 1350 C for Ni0.98Li0.02O and Zn0.98Al0.02O, respectively. The inter-diffusion couples were annealed at 900–1200 C for 160 h in ambient air. Electron Probe Micro Analysis (EPMA) was used to acquire diffusion profiles, followed by fitting to Ficks second law and Whipple–Le Claires models for bulk and grain-boundary diffusion calculation, respectively. Zn2+ diffused into Ni0.98Li0.02O mainly by bulk diffusion with an activation energy of 250  10 kJ/mol, whereas Ni2+ diffused into Zn0.98Al0.02O by both bulk and enhanced grain boundary diffusion with activation energies of 320  120 kJ/mol and 245  50 kJ/mol, respectively. The amount of Al3+ diffused from the Al-doped ZnO into the NiO phase was too small for a corresponding diffusion coefficient to be calculated. Li-ion distribution and diffusivity were not determined due to lack of analyzer sensitivity for Li. The bulk and effective diffusivities of Zn2+ and Ni2+ into NiO and ZnO enable prediction of inter-diffusion lengths as a function of time and temperature, allowing estimates of device performance, stability, and lifetimes at different operation temperatures.
Keywords NiO, ZnO, Cation diffusion, Grain-boundary diffusion, p-n junction
Remark https://doi.org/10.1016/j.ssi.2018.03.011
Link

Electrochemical promotion of nanodispersed Ru-Co catalysts for the hydrogenation of CO2

Authors A. Kotsirasa, I. Kalaitzidoua, D. Grigorioua, A. Symillidisa, M. Makria, A. Katsaounisa, C.G. Vayenas
Source
Applied Catalysis B: Environmental
Volume: 232, Pages: 60-68
Time of Publication: 2018
Abstract Electrochemical promotion of the CO2 hydrogenation to CH4 and CO on a nanodispersed Ru-Co catalyst has been achieved via slurry deposition of the nanodispersed catalyst on an interlayer Ru film deposited on a BZY (BaZr0.85Y0.15O3) proton conducting solid electrolyte disc. The effect of current is nonFaradaic, with Faradaic efficiency values as high as 60 and leads to a reversible variation of the selectivity to CH4 between 16% and 41%. Due to thermal spillover of protons on the Ru-Co catalyst surface, the open circuit selectivity to CO is quite high, i.e. up to 84% and similar values are obtained via negative potential application, i.e. proton supply to the Ru catalyst film deposited on BZY before the deposition of the nanodispersed catalyst. These results underline the similarity between electrochemical promotion and metal support interactions when using proton conducting supports. They also show the usefulness of electrochemical promotion for mechanistic investigations. The electrochemical promotion of nanodispersed catalysts is a promising step for the practical utilization of electrochemical promotion.
Keywords Electrochemical promotion, EPOC, NEMCA effect, CO2 hydrogenation, Dispersed catalyst, BZY
Remark https://doi.org/10.1016/j.apcatb.2018.03.031
Link

Structural transformations, water incorporation and transport properties of tin-substituted barium indate

Authors Kacper Cichy, Wojciech Skubid, Konrad Świerczek
Source
Journal of Solid State Chemistry
Volume: 262, Pages: 58-67
Time of Publication: 2018
Abstract Incorporation of water into tin-substituted BaIn1-xSnxO3-δ (x = 0.1–0.3) is shown to influence crystal structure at room temperature, structural transformations at high temperatures and ionic transport properties of the materials. Increasing tin content stabilizes oxygen vacancy-disordered perovskite-type phase, which together with large changes of the unit cell volume occurring during hydration and dehydration processes, result in a complex structural behavior, as documented by high-temperature X-ray diffraction and thermogravimetric studies. Impedance spectroscopy measurements at elevated temperatures (350–800 C) revealed very high proton conductivity in BaIn.8Sn.2O3-δ, exceeding 1.110−3 S cm−1 at 500 C, with high values of the transference number in wet air. At the same time, relaxation kinetics of the electrical conductivity showed a monotonous nature, which indicates negligible component of the electronic hole conductivity in the hydrated material. The oxides are extremely moisture-sensitive, which results in a significant mechanical stability problems, affecting possibility to prepare electrolyte membranes.
Keywords Barium indate, Hydration, Structural transformations, Proton conductivity, Relaxation experiments
Remark https://doi.org/10.1016/j.jssc.2018.03.004
Link

Single-crystal x-ray diffraction and impedance spectroscopy investigations of the RbxCs1-xH2PO4 (0≤x≤1) proton conductor series

Authors A.G. Goos, A.J. Encerrado Manriquez, H. Martinez, A.D. Price, C.E. Botez
Source
Journal of Physics and Chemistry of Solids
Volume: 118, Pages: 200-210
Time of Publication: 2018
Abstract We have used single-crystal x-ray diffraction to investigate the structural modifications induced by Rb-doping of the superprotonic conductor CsH2PO4. We found that the monoclinic P21/m CsH2PO4 modification persists within the RbxCs1-xH2PO4 (0 ≤ x ≤ 1) series upon Rb-doping from x = 0.1 to x = 0.7. Rb0.8Cs0.2H2PO4 (x = 0.8), however, exhibits a previously unreported P21/c monoclinic phase, where the mirror plane is lost and disorder is present in the PO4 tetrahedra even at room temperature. Higher levels of x display a tetragonal I-42d unit cell isomorphic with the known structure of RbH2PO4. The temperature dependence of the proton conductivity determined from impedance spectroscopy data collected within the 160⁰C-250 C range is also markedly different at high Rb-doping levels, x ≥ 0.8. Finally, we found that Rb0.9Cs0.1H2PO4 undergoes a transition from its room-temperature tetragonal I-42d phase to an intermediate-temperature monoclinic P21/m modification at a significantly lower temperature (∼80 C) than its RbH2PO4 counterpart (∼120 C).
Remark https://doi.org/10.1016/j.jpcs.2018.03.011
Link

Performance evaluation of Mn and Fe doped SrCo 0.9 Nb 0.1 O 3-δ cathode for IT-SOFC application

Authors Lokesh Bele, R.K. Lenka, P.K. Patro, L.M. uhmood, T. Mahata and P.K. Sinha
Source
IOP Conference Series: Materials Science and Engineering
Volume: 310
Abstract Cathode materials of Mn and Fe doped SrCo0.9Nb0.1O3-δ, are synthesized by solid state route for intermediate temperature fuel cell applications. Phase pure material is obtained after calcining the precursors at 1100oC. Phase compatibility is observed between this novel cathode material with gadolinia doped ceria (GDC)electrolyte material as reflected in the diffraction pattern. The state of art YSZ electrolyte is not compatible with this cathode material. Average thermal expansion coefficient of the material varies between 17 to 22 X 10-6 K-1 on doping, from room temperature to 800 oC. Increase in thermal expansion coefficient is observed with Mn and Fe doping associated with the loss of oxygen from the crystal. The electrical conductivity of the cathode material decreases with Fe and Mn doping. Mn doped samples show lowest conductivity. From the symmetric cell measurement lower area specific resistance (0.16 Ω-cm2) is obtained for un-doped samples, at 850 oC. From the initial results it can be inferred that Mn/Fe doping improves neither the thermal expansion coefficient nor the electrochemical activity.
Remark Link

Does the conductivity of interconnect coatings matter for solid oxide fuel cell applications?

Authors Claudia Goebel, Alexander G. Fefekos, Jan-Erik Svensson, Jan Froitzheim
Source
Journal of Power Sources
Volume: 383, Pages: 110-114
Time of Publication: 2018
Abstract The present work aims to quantify the influence of typical interconnect coatings used for solid oxide fuel cells (SOFC) on area specific resistance (ASR). To quantify the effect of the coating, the dependency of coating thickness on the ASR is examined on Crofer 22 APU at 600 C. Three different Co coating thicknesses are investigated, 600 nm, 1500 nm, and 3000 nm. Except for the reference samples, the material is pre-oxidized prior to coating to mitigate the outward diffusion of iron and consequent formation of poorly conducting (Co,Fe)3O4 spinel. Exposures are carried out at 600 C in stagnant laboratory air for 500 h and subsequent ASR measurements are performed. Additionally the microstructure is investigated with scanning electron microscopy (SEM). On all pre-oxidized samples, a homogenous dense Co3O4 top layer is observed beneath which a thin layer of Cr2O3 is present. As the ASR values range between 7 and 12 mΩcm2 for all pre-oxidized samples, even though different Co3O4 thicknesses are observed, the results strongly suggest that for most applicable cases the impact of the coating on ASR is negligible and the main contributor is Cr2O3.
Keywords Solid oxide fuel cell, Interconnect, Corrosion, Coating, Area specific resistance, Cr2O3
Remark https://doi.org/10.1016/j.jpowsour.2018.02.060
Link

Amorphous-cathode-route towards low temperature SOFC

Authors Andrea Cavallaro, Stevin S. Pramana, Enrique Ruiz-Trejo, Peter C. Sherrell, Ecaterina Ware, John A. Kilner and Stephen J. Skinner
Source
Volume: 2, Pages: 862-875
Time of Publication: 2018
Abstract Lowering the operating temperature of solid oxide fuel cell (SOFC) devices is one of the major challenges limiting the industrial breakthrough of this technology. In this study we explore a novel approach to electrode preparation employing amorphous cathode materials. La0.8Sr0.2CoO3−δ dense films have been deposited at different temperatures using pulsed laser deposition on silicon substrates. Depending on the deposition temperature, textured polycrystalline or amorphous films have been obtained. Isotope exchange depth profiling experiments reveal that the oxygen diffusion coefficient of the amorphous film increased more than four times with respect to the crystalline materials and was accompanied by an increase of the surface exchange coefficient. No differences in the surface chemical composition between amorphous and crystalline samples were observed. Remarkably, even if the electronic conductivities measured by the Van Der Pauw method indicate that the conductivity of the amorphous material was reduced, the overall catalytic properties of the cathode itself were not affected. This finding suggests that the rate limiting step is the oxygen mobility and that the local electronic conductivity in the amorphous cathode surface is enough to preserve its catalytic properties. Different cathode materials have also been tested to prove the more general applicability of the amorphous-cathode route.
Remark DOI: 10.1039/C7SE00606C
Link

Stability of the superprotonic conduction of (1-x)CsH2PO4/xSiO2 (0 ≤ x ≤ 0.3) composites under dry and humid environments

Authors J.H.Leal, H.Martinez, I.Martinez, A.D.Price, A.G.Goos, C.E.Botez
Source
Materials Today Communications
Volume: 15, Pages: 11-17
Time of Publication: 2018
Abstract We have used temperature- and time-resolved electrochemical impedance spectroscopy, x-ray diffraction, and thermal analysis methods to investigate the effect of mixing CsH2PO4 with nano-silica on the superprotonic conduction of this solid acid. We collected data on (1-x)CsH2PO4/xSiO2 (0 ≤ x ≤ 0.3) composites in dry (air) and humid (PH2O ∼ 0.38 atm) environments at temperatures below and above the superprotonic transition of CsH2PO4 (TSP ∼ 234 C). We first observed that a three-order-of-magnitude proton conductivity jump occurred in the unmixed sample (x = 0) at TSP, even under dry conditions and despite chemical changes (dehydration). We also found that the proton conductivity of the x = 0.1, 0.2 and 0.3 composites measured at T = 260 C in air is nearly one order of magnitude greater than that of the unmixed phosphate (x = 0). Even more significantly, we found that humid sample environments have no effect on the stability of the proton conductivity of the x = 0.2 composite measured over a 10 h timespan at temperatures above TSP. This is contrary to the behavior of the x = 0 sample, which is known [31] to be stable under humid conditions, but undergoes a three-order-of-magnitude proton conductivity drop in air.
Keywords Superprotonic phase, Composite materials, X-ray diffraction, Impedance spectroscopy
Remark https://doi.org/10.1016/j.mtcomm.2018.02.021
Link

Co-deficient PrBaCo2−xO6−δ perovskites as cathode materials for intermediate-temperature solid oxide fuel cells: Enhanced electrochemical performance and oxygen reduction kinetics

Authors Likun Zhang, Shuli Li, Tian Xia, Liping Sun, Lihua Huo, Hui Zhao
Source
International Journal of Hydrogen Energy
Volume: 43, Issue: 7, Pages: 3761-3775
Time of Publication: 2018
Abstract Co-deficient PrBaCo2−xO6−δ perovskites (x = 0, 0.02, 0.06 and 0.1) are synthesized by a solid-state reaction, and the effects of Co-deficiency on the crystal structure, oxygen nonstoichiometry and electrochemical properties are investigated. The PrBaCo2−xO6−δ samples have an orthorhombic layered perovskite structure with double c axis. The degree of oxygen nonstoichiometry increases with decreasing Co content (0 ≤ x ≤ 0.06) and then slightly decreases at x = 0.1. All the samples exhibit the electrical conductivity values of >300 S cm−1 in the temperature range of 100–800 C in air, which match well the requirement of cathode. With significantly enhanced electrochemical performance and good chemical compatibility between PrBaCo2−xO6−δ and CGO, this system of Co-deficient perovskite is promising cathode material for IT-SOFCs. Among all these components, PrBaCo1.94O6−δ gives lowest polarization resistance of 0.059 Ω cm2 at 700 C in air. When tested as cathode in fuel cell, the anode-supported Ni-YSZ|YSZ|CGO|PrBaCo1.94O6−δ cell delivers a maximum peak power density of 889 mW cm−2 at 650 C, which is higher than that of PrBaCoO6−δ cathode-based cell (764 mW cm−2). The oxygen reduction kinetics at the PrBaCo1.94O6−δ cathode interface is also explored, and the rate-limiting steps for oxygen reduction reaction are determined.
Keywords Intermediate-temperature solid oxide fuel cells, Cathode material, Layered perovskite, Electrochemical performance, Oxygen reduction kinetics
Remark https://doi.org/10.1016/j.ijhydene.2018.01.018
Link

Deposition of nickel oxide-yttria stabilized zirconia thin films by reactive magnetron sputtering

Authors A.A .Solovyev, A.M. Lebedynskiy, A.V. Shipilova, I.V.Ionov, E.A. Smolyanskiy, A.L. Lauk, G.E. Remnev
Source
International Journal of Hydrogen Energy
Time of Publication: 2018
Abstract Nickel oxide-yttria stabilized zirconia (NiO-YSZ) thin films were reactively sputter-deposited by pulsed direct current magnetron sputtering from the Ni and Zr-Y targets onto heated commercial NiO-YSZ substrates. The microstructure and composition of the deposited films were investigated with regard to application as thin anode functional layers (AFLs) for solid oxide fuel cells (SOFCs). The porosity and microstructure of both as-deposited and annealed at 1200 C for 2 h AFLs were studied by scanning electron microscopy and X-ray diffractometry and controlled by changing the deposition process parameters. The results show that annealing in air at 1200 C is required to improve film crystallinity and structural homogeneity. NiO-YSZ films have pores and grains of several hundred nanometers in size after reduction in hydrogen. Adhesion of deposited films was evaluated by scratch test. Anode-supported solid oxide fuel cells with the magnetron sputtered anode functional layer, YSZ electrolyte and La0.6Sr0.4Co0.2Fe0.8O3/Ce0.9Gd0.1O2 (LSCF/CGO) cathode were fabricated and tested. Influence of thin anode functional layer on performance of anode-supported SOFCs was studied. It was shown that electrochemical properties of the single fuel cells depend on the NiO volume content in the NiO-YSZ anode functional layer. Microstructural changes of NiO-YSZ layers after nickel reduction-oxidation (redox) cycling were studied. After nine redox cycles at 750 C in partial oxidation conditions, the cell with the anode NiO-YSZ layer showed stable open circuit voltage values with the power density decrease by 11% only.
Keywords Solid oxide fuel cells, Magnetron sputtering, Thin-film anode, Microstructure, Redox cycling
Remark Available online 7 February 2018, https://doi.org/10.1016/j.ijhydene.2018.01.076
Link

Solid oxide fuel cells with apatite-type lanthanum silicate-based electrolyte films deposited by radio frequency magnetron sputtering

Authors Yi-Xin Liu, Sea-Fue Wang, Yung-Fu Hsu, Chi-Hua Wang
Source
Journal of Power Sources
Volume: 381, Pages: 101-106
Time of Publication: 2018
Abstract In this study, solid oxide fuel cells (SOFCs) containing high-quality apatite-type magnesium doped lanthanum silicate-based electrolyte films (LSMO) deposited by RF magnetron sputtering are successfully fabricated. The LSMO film deposited at an Ar:O2 ratio of 6:4 on an anode supported NiO/Sm0.2Ce08O2-δ (SDC) substrate followed by post-annealing at 1000 C reveals a uniform and dense c-axis oriented polycrystalline structure, which is well adhered to the anode substrate. A composite SDC/La06Sr04Co02Fe08O3-δ cathode layer is subsequently screen-printed on the LSMO deposited anode substrate and fired. The SOFC fabricated with the LSMO film exhibits good mechanical integrity. The single cell with the LSMO layer of ≈2.8 μm thickness reports a total cell resistance of 1.156 and 0.163 Ωcm2, open circuit voltage of 1.051 and 0.982 V, and maximum power densities of 0.212 and 1.490 Wcm−2 at measurement temperatures of 700 and 850 C, respectively, which are comparable or superior to those of previously reported SOFCs with yttria stabilized zirconia electrolyte films. The results of the present study demonstrate the feasibility of deposition of high-quality LSMO films by RF magnetron sputtering on NiO-SDC anode substrates for the fabrication of SOFCs with good cell performance.
Keywords Solid oxide fuel cell, Sputtering, Electrolyte Doped lanthanum silicate
Remark https://doi.org/10.1016/j.jpowsour.2018.02.007
Link

Electrical conductivity of NiMo–based double perovskites under SOFC anodic conditions

Authors Sabrina Presto, Pravin Kumar, Salil Varma, Massimo Viviani, Prabhakar Singh
Source
International Journal of Hydrogen Energy
Volume: 43, Issue: 9, Pages: 4528-4533
Time of Publication: 2018
Abstract Three different materials are prepared by chemical reaction route, Sr2NiMoO6 (SNM00), Sr1.96La004NiMoO6 (SLNM04) and Sr1.99Ce0.01NiMoO6 (SCNM01) and conductivity is measured under reducing atmosphere, in order to study their suitability as anode materials in SOFC application. Selected materials correspond to compositions reported with highest conductivity in air at operative temperatures of a SOFC among the systems SLNM (Sr2−xLaxNiMoO6, 0.02 ≤ x ≤ 0.10) and SCNM (Sr2−xCexNiMoO6, 0.01 ≤ x ≤ 0.05). The end member Sr2NiMoO6 (SNM) is also considered as reference. Their conductivities considerably increase in wet hydrogen and follow Arrhenius behavior with lower activation energy. Effects of reduction on microstructure and phase stability are also studied by scanning electron microscopy and X–ray diffraction. The enhancement in conductivity is discussed in terms of defects chemistry. Amongst all measured samples, SLNM04 shows the highest conductivity in reducing atmosphere without phase degradation, which makes it a promising anode material for Solid Oxide Fuel Cells (SOFC).
Keywords Double perovskite Reduction Electrical conductivity Anodic materials SOFC
Remark https://doi.org/10.1016/j.ijhydene.2018.01.066
Link

Effect of sintering temperature on the performance of composite La0.6Sr0.4Co0.2Fe0.8O3–Ce0.9Gd0.1O2 cathode for solid oxide fuel cells

Authors A.A. Solovyev, I.V. Ionov, A.V. Shipilova, P.D. Maloney
Source
Journal of Electroceramics
Time of Publication: 2018
Abstract Studied here are the effects of sintering temperature of La0.6Sr0.4Co0.2Fe0.8O3-Ce0.9Gd0.1O2 (LSCF–CGO) cathodes on their microstructure and performance of intermediate-temperature solid oxide fuel cells (IT-SOFC). Phase composition, microstructure and electrochemical properties were investigated by X-ray powder diffraction (XRD), scanning electron microscopy and current-voltage characteristics measurement, respectively. The electrochemical performances of Ni–YSZ anode-supported SOFC having YSZ electrolyte (4 μm) with CGO interlayer (2 μm) are studied with LSCF–CGO (50:50 wt%) cathodes in the temperature range 600–800 C using H2 as fuel and air as oxidant. The cathode microstructure was found to be less dense and to contain smaller grains as the sintering temperature was decreased in the range 1250–1150 C. Results reveal that sintering temperature and electrode morphology have strong influence on electrochemical performances of the IT-SOFC. Highest maximum power density of ∼1.26 W/cm2 is achieved during cell testing at 800 C with a cathode sintered at 1200 C. However, cells with in-situ sintered LSCF–CGO cathode showed highest power density at 600 C (0.48 W/cm2) because there is no particle coarsening at low sintering temperatures.
Keywords LSCF–CGO, Composite cathode, Microstructure,, Performanc, Intermediate-temperature solid oxide fuel cells
Remark https://doi.org/10.1007/s10832-018-0114-5, First Online: 29 January 2018
Link

Proton and oxygen ion conductivity in the pyrochlore/fluorite family of Ln2−xCaxScMO7−δ (Ln = La, Sm, Ho, Yb; M = Nb, Ta; x = 0, 0.05, 0.1) niobates and tantalates

Authors A. V. Shlyakhtina, K. S. Pigalskiy, D. A. Belov, N. V. Lyskov, E. P. Kharitonova, I. V. Kolbanev, A. B. Borunova, O. K. Karyagina, E. M. Sadovskaya, V. A. Sadykov and N. F. Eremeev
Source
Dalton Transaction
Volume: 47, Pages: 2376-2392
Time of Publication: 2018
Abstract The tolerance factor is a good criterion to understand the structural transitions in Ln2−xCaxScMO7−δ (Ln = La, Sm, Ho, Yb; M = Nb, Ta; x = 0, 0.05, 0.1). Decreasing the Ln ionic radius in Ln2ScNb(Ta)O7 leads to a morphotropic transition from a pyrochlore to a fluorite-like structure. Ca2+-doping leads to a pyrochlore-to-fluorite transition in Ln2−xCaxScMO7−δ (Ln = La, Sm) and a fluorite-to-pyrochlore transition in Ho2−xCaxScNbO7−δ. Proton contribution to the total conductivity was observed for Ln2−xCaxScNb(Ta)O7−δ (Ln = La, Sm; x = 0, 0.05, 0.1) 3+/5+ pyrochlores and the maximum proton contribution was shown by Sm1.9Ca0.1ScMO6.95 (M = Nb, Ta), which are located at the boundary between pyrochlores and fluorites (comparative study of electrical conduction and oxygen diffusion). Proton conduction of Sm1.9Ca0.1ScNbO6.95 and Sm1.9Ca0.1ScTaO6.95 pyrochlores persists up to 800 and 850 C, respectively. The conductivity of fluorite-like Ho2−xCaxScNbO7−δ (x = 0, 0.05) and Yb2ScNbO7 is dominated by the oxygen ion transport, in accordance with their energy activation values 1.09–1.19 eV. The dielectric permittivity and TG studies were used for the investigation of oxygen vacancy dynamics and water incorporation into the Ln2−xCaxScNb(Ta)O7−δ (Ln = La, Sm, Ho, Yb; x = 0, 0.05, 0.1) lattice. It is shown that oxygen vacancy-related dielectric relaxation in the range of 550–650 C (ambient air), typical of pyrochlores and fluorites with pure oxygen ion conductivity, decreases and disappears for proton-conducting oxides.
Keywords Proton and oxygen ion conductivity, Pyrochlore/fluorite family
Remark DOI: 10.1039/C7DT03912C
Link

Iono-molecular Separation with Composite Membranes

Authors ABBAS ABDUL KADHIM KLAIF RIKABI, MARIANA BALABAN (CHELU), IULIA HARABOR, PAUL CONSTANTIN ALBU, MIRCEA SEGARCEANU, GHEORGHE NECHIFOR
Source
REV.CHIM.
Volume: 9 Time of Publication: 2016
Abstract The fast development of these methods in the recent years has been possible due to new materials developing, the boom of nanomaterials in the development of composite and hybrid materials and also due to developing of new techniques and technologies. This paper presents the composite membranes based on polysulfone and performance nanomaterials: polyaniline and magnetic nanoparticles synthesis and characterization. Composite membranes (PSf-PANI and PSf-magnetite) have been produced by phase inversion by immersion - precipitation from a polysulfone in N-methyl pyrrolidone dispersion solution in which were dispersed polyaniline or magnetic nanoparticles. The prepared composite membranes were morphologically and structurally characterized using techniques and specific measurments: FT-IR, SEM, AFM, UV VIS, DSC, dielectric spectroscopy, solvents permeation and bovine serum albumin retention.Membranes pore size indicate their use in micro and ultrafiltration (12% in the case of PSF membrane and 12% for PSf - PANI) or in the field of microfiltration and membrane sensor, 12% for magnetite - PSF membrane. The results show that water flows at 3-4 bar pressure, are increasing in the order: PSf membrane < PSf –magnetite membrane PSf –magnetite membrane > PSf-PANI membrane. In the case of alcohols flow, hydrocarbon chain has influence on flows and this correlates with hydrophily of membranes. Following bovine serum albumin retention tests, PSf-PANI membrane has the best performance (R> 95%), which correlates with the higher permeate flows.
Remark Link

Structural and electrochemical characterization of BaCe0.7Zr0.2Y0.05Zn0.05O3 as an electrolyte for SOFC-H

Authors Ahmed Afif, Nikdalila Radenahmad, Chee Ming Lim, Quintin Cheok, Md. Aminul Islam, Seikh Mohammad Habibur Rahman, Abul Kalam Azad
Source
IOP Conf. Series: Materials Science and Engineering
Volume: 121 Time of Publication: 2016
Abstract As a potential electrolyte for proton-conducting solid oxide fuel cells (SOFC-Hs)and to get better protonic conductivity and stability, zinc doped BCZY material has been found to be promising. In this study, we report a new composition of proton conductors BaCe0.7Zr0.2Y0.05Zn0.05O3 (BCZYZn5) which was investigated using XRD, SEM and conductivity measurements. Rietveld refinement of the XRD data revel a cubic perovskite structure with Pm-3m space group. BaCe0.7Zr0.2Y0.05Zn0.05O3 shows cell parameter a = 4.3452(9) . Scanning electron microscopy images shows that the grain sizes are large and compact which gives the sample high density and good protonic conductivity. The total conductivity in wet atmosphere is significantly higher than that of dry condition and the conductivity was found to be 0.276 x 10-3 Scm-1 and 0.204 x 10-3 Scm-1 at 600C in wet and dry Ar, respectively. This study indicated that perovskite electrolyte BCZYZn5 is a promising material for the next generation intermediate temperature solid oxide fuel cells (IT-SOFCs).
Remark Link

Enhanced O2 Flux of CaTi0.85Fe0.15O3−δ Based Membranes by Mn Doping

Authors Polfus, J. M., Xing, W., Riktor, M., Sunding, M. F., Dahl, P. I., Hanetho, S. M., Mokkelbost, T., Larring, Y., Fontaine, M.-L. and Bredesen, R.
Source
Journal of the American Ceramic Society
Volume: 99, Issue: 3, Pages: 1071–1078
Time of Publication: 2016
Abstract Dense symmetric membranes of CaTi0.85−xFe0.15MnxO3−δ (x = 0.1, 0.15, 0.25, 0.4) are investigated in order to determine the optimal Mn dopant content with respect to highest O2 flux. O2 permeation measurements are performed as function of temperature between 700C–1000C and as function of the feed side math formula ranging between 0.01 and 1 bar. X-ray photoelectron spectroscopy is utilized to elucidate the charge state of Mn, and synchrotron radiation X-ray powder diffraction (SR-XPD) is employed to investigate the structure symmetry and cell volume of the perovskite phase at temperatures up to 800C. The highest O2 permeability is found for x = 0.25 over the whole temperature and math formula ranges, followed by x = 0.4 above 850C. The O2 permeability for x = 0.25 reaches 0.01 mL(STP) min−1 cm−1 at 925C with 0.21 bar feed side math formula and Ar sweep gas. X-ray photoelectron spectroscopy indicates that the charge state of Mn changes from approx. +3 to +4 when x > 0.1, which implies that Mn mainly improves electronic conductivity for x > 0.1. The cell volume is found to decrease linearly with Mn content, which coincides with an increase in the activation energy of O2 permeability. These results are consistent with the interpretation of the temperature and math formula dependency of O2 permeation. The sintering behavior and thermal expansion properties are investigated by dilatometry, which show improved sinterability with increasing Mn content and that the thermal expansion coefficient decreases from 12.4 to 11.9 10−6 K−1 for x = 0 and x = 0.25, respectively.

Fabrication and characterization of La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF)-Ce0.9Gd0.1O1.95 (GDC) composite thick film for anode supported solid oxide fuel cells

Authors Atul P. Jamale, C. H. Bhosale, L. D. Jadhav
Source
Journal of Materials Science: Materials in Electronics
Volume: 27, Issue: 1, Pages: 795–799
Time of Publication: 2016
Abstract Nowadays, the commercialization of solid oxide fuel cell (SOFC) is impeded by the chemical compatibility and polarization losses in association with electrode/electrolyte interface. Thus, to minimize these difficulties, the thick film of LSCF-GDC (50:50 wt%) composite was deposited onto GDC electrolyte to form perfect LSCF-GDC/GDC structure. The chemically compatibility of LSCF-GDC upon sintering of 1000 C was confirmed from the X-ray diffraction studies. Typically, the film with 15 μm thickness possesses the porous structure, availing the free path for oxygen diffusion. The electrochemical impedance analysis of symmetric cell with LSCF-GDC as an electrode implies the relaxation of charge transfer and electrochemical reduction reaction with temperature. The NiO-GDC (30:70 wt%) supported SOFC with GDC and LSCF-GDC as an electrolyte and cathode, respectively was tested for their performance. The cell generates the maximum powder density of 315 μWcm−2 at 500 C.
Remark Link

Materials development: general discussion

Authors Raymond Gorte, John Vohs, Theis L. Skafte, Robert Kee, John Varcoe, Ian Metcalfe, Sune Dalgaard Ebbesen, Guntae Kim, Dehua Dong, San Ping Jiang, Ming Li, Tatsumi Ishihara, John Bgild Hansen, Beatriz Molero-Sanchez, Steven McIntosh, Helena Tllez, Alex Mo
Source
Faraday Discussions
Volume: 182, Pages: 307
Time of Publication: 2015
Remark Link

The Band Gap of BaPrO3 Studied by Optical and Electrical Methods

Authors Matthias Schrade, Anna Magras, Augustinas Galeckas, Terje J. Finstad, and Truls Norby
Source
Journal of the American Ceramic Society
Volume: 99, Issue: 2, Pages: 492–498
Time of Publication: 2016
Abstract We report on measurements of the electrical and optical properties of BaPrO3. The temperature dependences of the electrical conductivity σ and the Seebeck coefficient α of polycrystalline samples were studied over a wide temperature range (300C–1050C). At lower temperatures, the observed charge transport can be described as thermally activated hopping of electron-based small polarons with an activation energy of 0.37 eV. An observed change in temperature dependence of both σ and α around 700C was observed and interpreted as a transition from extrinsic to intrinsic carrier transport. The intrinsic conduction can be modeled with an apparent electrical band gap of ~2 eV. Optical absorption and emission spectroscopy in the UV–VIS–NIR range revealed a series of characteristic absorption thresholds and the type of optical transitions was identified by combining transmittance and diffuse-reflectance spectroscopy methods. An absorption edge of indirect type with onset at 0.6 eV is attributed to small polaron effects. The higher lying absorption thresholds of direct origin positioned at around 1.8 and 3.8 eV are correlated with thermal activation parameters from electrical measurements and discussed in terms of the band gap of BaPrO3.
Remark DOI: 10.1111/jace.13961
Link

Copper Iron Conversion Coating for Solid Oxide Fuel Cell Interconnects

Authors Jan Gustav Grolig, Patrik Alnegren, Jan Froitzheim, Jan-Erik Svensson
Source
Journal of Power Sources
Volume: 297, Pages: 534-539
Time of Publication: 2015
Abstract A conversion coating of iron and copper was investigated with the purpose of increasing the performance of Sanergy HT as a potential SOFC interconnect material. Samples were exposed to a simulated cathode atmosphere (air, 3 % H2O) for durations of up to 1000 h at 850 C. Their performance in terms of corrosion, chromium evaporation and electrical resistance (ASR) was monitored and compared to uncoated and cobalt-coated Sanergy HT samples. The copper iron coating had no negative effects on corrosion protection and decreased chromium evaporation by about 80%. An Area Specific Resistance (ASR) of 10 mΩcm2 was reached after 1000 h of exposure. Scanning Electron Microscopy revealed well adherent oxide layers comprised of an inner chromia layer and an outer spinel oxide layer.
Remark https://doi.org/10.1016/j.jpowsour.2015.06.139
Link

New alluaudite-related triple molybdates Na25Cs8R5(MoO4)24 (R = Sc, In): synthesis, crystal structures and properties

Authors Aleksandra A. Savina, Sergey F. Solodovnikov, Dmitry A. Belov, Zoya A. Solodovnikova, Sergey Yu. Stefanovich, Bogdan I. Lazoryak and Elena G. Khaikina
Source
New Journal of Chemistry
Volume: 41, Pages: 5450
Time of Publication: 2017
Abstract New triple molybdates Na25Cs8R5(MoO4)24 (R = Sc, In) were prepared as powders and ceramics by solid state reactions, and their single crystals were also obtained from melts by spontaneous сrystallization. The structures were determined by single crystal XRD analysis. The electrical conductivity of ceramics was measured by impedance spectroscopy. The crystal structures were determined in monoclinic sp. gr. P21/c, a = 14.0069(3) ,b = 12.6498(3) , c = 28.6491(6) , b = 90.007(1)1 (Sc) and a = 14.0062(2) , b = 12.6032(2) , c = 28.7138(4) ,b = 90.001(1)1 (In). Together with triclinic Na25Cs8Fe5(MoO4)24, the titled compounds form a distinctive family of pseudo-orthorhombic alluaudite-related structures with the parent sp. gr. Pbca. Its structural features are alluaudite-like polyhedral layers composed of pairs of edge-shared (R, Na)O6 and NaO6 octahedra connected by bridging MoO4 tetrahedra. The layers are joined together by means of interlayer MoO4 tetrahedra, thus forming open 3D frameworks with cavities filled with Cs+ and Na+ ions. The manner of stacking layers is somewhat different from the alluaudite type. The compounds undergo phase transitions at 668 (Sc) and 725 (In) K accompanied by an abrupt increase of electrical conductivity presumably Na+-ionic in nature. Above these transitions, the conductivity is as high as 10(3) Scm(-1), which makes Na25Cs8R5(MoO4)24 (R = Sc, In) promising solid state electrolytes.
Remark DOI: 10.1039/c7nj00202e
Link

Enhanced Flexible Thermoelectric Generators Based on Oxide–Metal Composite Materials

Authors Benjamin Geppert, Artur Brittner, Lailah Helmich, Michael Bittner, Armin Feldhoff
Source
Journal of Electronic Materials
Volume: 46, Issue: 4, Pages: 2356–2365
Time of Publication: 2017
Abstract The thermoelectric performance of flexible thermoelectric generator stripes was investigated in terms of different material combinations. The thermoelectric generators were constructed using Cu-Ni-Mn alloy as n-type legs while varying the p-type leg material by including a metallic silver phase and an oxidic copper phase. For the synthesis of Ca3Co4O9/CuO/Ag ceramic-based composite materials, silver and the copper were added to the sol–gel batches in the form of nitrates. For both additional elements, the isothermal specific electronic conductivity increases with increasing amounts of Ag and CuO in the samples. The amounts for Ag and Cu were 0 mol.%, 2 mol.%, 5 mol.%, 10 mol.%, and 20 mol.%. The phases were confirmed by x-ray diffraction. Furthermore, secondary electron microscopy including energy dispersive x-ray spectroscopy were processed in the scanning electron microscope and the transmission electron microscope. For each p-type material, the data for the thermoelectric parameters, isothermal specific electronic conductivity σ and the Seebeck coefficient α, were determined. The p-type material with a content of 5 mol.% Ag and Cu exhibited a local maximum of the power factor and led to the generator with the highest electric power output Pel.
Remark Link

Protonic Conduction in TiP2O7

Authors V. Nalini, T.Norby, A.M. Anuradha
Source
Solid State Ionics: Advanced Materials for Emerging Technologies
Remark Link

Crystal structure and proton conductivity of BaSn 0.6 Sc 0.4 O 3  d : insights from neutron powder di ff raction and solid-state NMR spectroscopy

Authors Francis G. Kinyanjui, Stefan T. Norberg, Christopher S. Knee, Istaq Ahmed, Stephen Hull, Lucienne Buannic, Ivan Hung, Zhehong Gan, Fr ́ed ́eric Blanc, Clare P. Grey and Sten G. Eriksson
Source
J.Mater.Chem.A
Volume: 4, Issue: 14, Pages: 5088-5101
Time of Publication: 2016
Abstract The solid-state synthesis and structural characterisation of perovskite BaSn1−xScxO3−δ (x = 0.0, 0.1, 0.2, 0.3, 0.4) and its corresponding hydrated ceramics are reported. Powder and neutron X-ray diffractions reveal the presence of cubic perovskites (space group Pm[3 with combining macron]m) with an increasing cell parameter as a function of scandium concentration along with some indication of phase segregation. 119Sn and 45Sc solid-state NMR spectroscopy data highlight the existence of oxygen vacancies in the dry materials, and their filling upon hydrothermal treatment with D2O. It also indicates that the Sn4+ and Sc3+ local distribution at the B-site of the perovskite is inhomogeneous and suggests that the oxygen vacancies are located in the scandium dopant coordination shell at low concentrations (x ≤ 0.2) and in the tin coordination shell at high concentrations (x ≥ 0.3). 17O NMR spectra on 17O enriched BaSn1−xScxO3−δ materials show the existence of Sn–O–Sn, Sn–O–Sc and Sc–O–Sc bridging oxygen environments. A further room temperature neutron powder diffraction study on deuterated BaSn0.6Sc0.4O3−δ refines the deuteron position at the 24k crystallographic site (x, y, 0) with x = 0.579(3) and y = 0.217(3) which leads to an O–D bond distance of 0.96(1) and suggests tilting of the proton towards the next nearest oxygen. Proton conduction was found to dominate in wet argon below 700 C with total conductivity values in the range 1.8 10−4 to 1.1 10−3 S cm−1 between 300 and 600 C. Electron holes govern the conduction process in dry oxidizing conditions, whilst in wet oxygen they compete with protonic defects leading to a wide mixed conduction region in the 200 to 600 C temperature region, and a suppression of the conductivity at higher temperature.
Remark DOI: 10.1039/c5ta09744d
Link

Microstructural design of CaMnO3 and its thermoelectric proprieties.

Author Natalia Maria Mazur
Source
dissertation
Time of Publication: 2015
Remark Norwegian University of Science and Technology, Department of Materials Science and Engineering
Link

Effect of Firing Temperature on the Kinetics of Oxygen Reduction in La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) Cathodes for Solid Oxide Fuel Cells

Author Brage Braathen Kjeldby
Source
dissertation
Time of Publication: 2015
Remark Norwegian University of Science and Technology, Department of Materials Science and Engineering
Link

DC-bias dependent impedance spectroscopy of BaTiO3–Bi(Zn1/2Ti1/2)O3 ceramics

Authors Nitish Kumar, Eric A. Patterson, Till Frmling and David P. Cann
Source
J. Mater. Chem. C
Volume: 4, Pages: 1782-1786
Time of Publication: 2016
Remark DOI: 10.1039/C5TC04247J
Link

Surface Protonics Promotes Catalysis

Authors R. Manabe, S. Okada, R. Inagaki, K. Oshima, S. Ogo & Y. Sekine
Source
Nature Scientific Reports 6
Time of Publication: 2016
Abstract Catalytic steam reforming of methane for hydrogen production proceeds even at 473 K over 1 wt% Pd/CeO2 catalyst in an electric field, thanks to the surface protonics. Kinetic analyses demonstrated the synergetic effect between catalytic reaction and electric field, revealing strengthened water pressure dependence of the reaction rate when applying an electric field, with one-third the apparent activation energy at the lower reaction temperature range. Operando–IR measurements revealed that proton conduction via adsorbed water on the catalyst surface occurred during electric field application. Methane was activated by proton collision at the Pd–CeO2 interface, based on the inverse kinetic isotope effect. Proton conduction on the catalyst surface plays an important role in methane activation at low temperature. This report is the first describing promotion of the catalytic reaction by surface protonics.
Remark doi:10.1038/srep38007
Link

Structural- and Compositional Investigations of Grain Boundaries in Y-Doped BaZrO3 A proton-conducting electrolyte for electrochemical applications

Author Adrian Lervik
Source
Master’s Thesis
Time of Publication: 2016
Remark University of Oslo
Link

Comparative study of the electrochemical promotion of CO2 hydrogenation on Ru using Na+, K+, H+ and O2 − conducting solid electrolytes

Authors I.Kalaitzidou, M. Makri, D. Theleritis, A. Katsaounis, C.G. Vayenas
Source
Surface Science
Volume: 646, Pages: 194-203
Time of Publication: 2016
Abstract The kinetics and the electrochemical promotion of the hydrogenation of CO2 to CH4 and CO are compared for Ru porous catalyst films deposited on Na+, K+, H+ and O2 − conducting solid electrolyte supports. It is found that in all four cases increasing catalyst potential and work function enhances the methanation rate and selectivity. Also in all four cases the rate is positive order in H2 and exhibits a maximum with respect to CO2. At the same time the reverse water gas shift reaction (RWGS) which occurs in parallel exhibits a maximum with increasing and is positive order in CO2. Also in all cases the selectivity to CH4 increases with increasing and decreases with increasing . These results provide a lucid demonstration of the rules of chemical and electrochemical promotion which imply that (∂r/∂Φ)(∂r/∂pD) > 0 and (∂r/∂Φ)(∂r/∂pA) < 0, where r denotes a catalytic rate, Φ is the catalyst work function and pD and pA denote the electron donor and electron acceptor reactant partial pressures respectively.
Keywords Electrochemical promotion of catalysis, Ion conducting support, Hydrogenation of CO2, Ruthenium catalyst, Rules of promotion, Metal–support interactions
Remark https://doi.org/10.1016/j.susc.2015.09.011
Link

Defect mechanisms in BaTiO3-BiMO3 ceramics

Authors Nitish Kumar, Eric A. Patterson, Till Frmling, Edward P. Gorzkowski, Peter Eschbach, Ian Love, Michael P. Mller, Roger A. De Souza, Julie Tucker, Steven R. Reese and David P. Cann
Source
Journal of the American Ceramic Society
Time of Publication: 2018
Abstract Often, addition of BiMO3 to BaTiO3 (BT) leads to improvement in resistivity with a simultaneous shift to n-type conduction from p-type for BT. In considering one specific BiMO3 composition, that is, Bi(Zn1/2Ti1/2)O3 (BZT), several prospective candidates for the origin of this n-type behavior in BT-BZT were studied—loss of volatile cations, oxygen vacancies, bismuth present in multiple valence states and precipitation of secondary phases. Combined x-ray and neutron diffraction, prompt gamma neutron activation analysis and electron energy loss spectroscopy suggested much higher oxygen vacancy concentration in BT-BZT ceramics (>4%) as compared to BT alone. X-ray photoelectron spectroscopy and x-ray absorption spectroscopy did not suggest the presence of bismuth in multiple valence states. At the same time, using transmission electron microscopy, some minor secondary phases were observed, whose compositions were such that they could result in effective donor doping in BT-BZT ceramics. Using experimentally determined thermodynamic parameters for BT and slopes of Krger-Vink plots, it has been suggested that an ionic compensation mechanism is prevalent in these ceramics instead of electronic compensation. These ionic defects have an effect of shifting the conductivity minimum in the Krger-Vink plots to higher oxygen partial pressure values in BT-BZT ceramics as compared to BT, resulting in a significantly higher resistivity values in air atmosphere and n-type behavior. This provides an important tool to tailor transport properties and defects in BT-BiMO3 ceramics, to make them better suited for dielectric or other applications.
Remark DOI: 10.1111/jace.15403, Version of Record online: 8 JAN 2018
Link

The Effect of Ni Doping on the Performance and Electronic Structure of LSCF Cathodes Used for IT-SOFCs

Authors Alessandro Longo, Leonarda F. Liotta, Dipanjan Banerjee, Valeria La Parola, Fabrizio Puleo, Chiara Cavallari, Christoph J. Sahle, Marco Moretti Sala, and Antonino Martorana
Source
J. Phys. Chem.: C
Time of Publication: 2017
Abstract We investigated the effect of nickel doping on the electronic structure and performance of nanostructured La0.6Sr0.4Co0.2Fe0.8–0.03Ni0.03O3−δ prepared by the one-pot sol–gel method. The commercial undoped La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF0.8) was used as reference. Moreover, for comparison, Ni (3 mol %) was deposited by wetness impregnation over the La0.6Sr0.4Co0.2Fe0.8O3−δ. We show by in situ X-ray absorption spectroscopy at 900 C under air flow that nickel enters the B perovskite site of the material and favors the stabilization of the cobalt oxidation state, as evidenced by the delay in the decrease of the average Co valence with respect to undoped samples. Our results are further supported by in situ X-ray Raman spectroscopy (XRS) that allowed us to monitor the temperature evolution of the O K-edge. XRS evidences that nickel-doped LSCF shows unmodified O2p-TM3d density of states, which proves that the Co oxidation state is preserved. Electrochemical impedance spectroscopy measurements were carried out over half-cell systems consisting of LSCF-based materials deposited onto a Ce0.8Gd0.2O2−δ electrolyte. The improvement of the electrochemical performances of the Ni-doped La0.6Sr0.4Co0.2Fe0.8–0.03Ni0.03O3−δ sample with respect to a reference Ni-impregnated LSCF is attributed to the stabilization of the TM-O6 structural units, which were recently proposed as the functional units for oxygen reduction.
Remark DOI: 10.1021/acs.jpcc.7b07626
Link

Protonic Conductors for Intermediate Temperature Fuel Cell Electrolytes: Superprotonic CsH2PO4 Stabilization and in-Doped SnP2O7 Structure Study

Author Heber Jair Martinez Salinas
Source
Dissertation
Time of Publication: 2017
Remark The University of Texas at El Paso
Link

Optimisation of growth parameters to obtain epitaxial Y-doped BaZrO3 proton conducting thin films

Authors A. Magras, B. Ballesteros, R. Rodrguez-Lamas, M.F. Sunding, J. Santiso
Source
Volume: 314, Pages: 9–16
Time of Publication: 2018
Abstract We hereby report developments on the fabrication and characterization of epitaxial thin films of proton conducting Y-doped BaZrO3 (BZY) by pulsed laser deposition (PLD) on different single crystal substrates (MgO, GdScO3, SrTiO3, NdGaO3, LaAlO3 and sapphire) using Ni-free and 1% Ni-containing targets. Pure, high crystal quality epitaxial films of BZY are obtained on MgO and on perovskite-type substrates, despite the large lattice mismatch. The deposition conditions influence the morphology, cell parameters and chemical composition of the film, the oxygen partial pressure during film growth being the most determining. Film characterization was carried out using X-ray diffraction, transmission electron and atomic force microscopies, wavelength dispersive X-ray spectroscopy and angle-resolved X-ray photoelectron spectroscopy. All films show a slight tetragonal distortion that is not directly related to the substrate-induced strain. The proton conductivity of the films depends on deposition conditions and film thickness, and for the optimised conditions its total conductivity is slightly higher than the bulk conductivity of the target material (3 mS/cm at 600 C, in wet 5% H2/Ar). The conductivities are, however, more than one order of magnitude lower than the highest reported in literature and possible reasoning is elucidated in terms of local and extended defects in the films.
Keywords BaZrO3; Thin film; Electrolyte; Proton conductivity; SOFC; PC-SOFC
Remark https://doi.org/10.1016/j.ssi.2017.11.002
Link

Improvement of thermoelectric properties of lanthanum cobaltate by Sr and Mn co-substitution

Authors Ashutosh Kumar, D. Sivaprahsam, Ajay D. Thakur
Source
Journal of Alloys and Compounds
Volume: 735, Pages: 1787–1791
Time of Publication: 2018
Abstract We report thermoelectric (TE) properties of Sr and Mn co-substituted LaCoO3 system from room temperature to 700 K. Sr-substitutions at La and Mn at Co site in LaCoO3 improves the electrical conductivity (σ). Thermal conductivity (κ) of all the samples increases with the increase in temperature but decreases with the substitution in LaCoO3. An estimation of the electronic thermal conductivity (κe) suggests a dominant phonon contribution to thermal conductivity in this system. A maximum value of the figure of merit is 0.14 at 480 K for La0.95Sr0.05Co0.95Mn0.05O3.
Keywords Powders: solid-state reaction; Thermal conductivity; Electrical conductivity; Perovskites
Remark https://doi.org/10.1016/j.jallcom.2017.11.334
Link

Microstructural engineering and use of efficient poison resistant Au-doped Ni-GDC ultrathin anodes in methane-fed solid oxide fuel cells

Authors F.J. Garcia-Garciaa, F. Yubero, A.R. Gonzlez-Elipe, R.M. Lambert
Source
International Journal of Hydrogen Energy
Volume: 43, Issue: 2, Pages: 885–893
Time of Publication: 2018
Abstract Ultrathin porous solid oxide fuel cell (SOFC) anodes consisting of nickel-gadolinia-doped-ceria (Ni-GDC) cermets with a unique porous micro-columnar architecture with intimate contact between the GDC and the Ni phases were made by magnetron sputtering at an oblique deposition angle and characterised in detail by a variety of methods prior to use in hydrogen or methane-fuelled SOFCs. These Ni-GDC anodes exhibited excellent transport properties, were robust under thermal cycling and resistant to delamination from the underlying yttria-stabilised zirconia electrolyte. Similarly prepared Au-doped Ni-GDC anodes exhibited the same morphology, porosity and durability. The gold associated exclusively with the Ni component in which it was present as a surface alloy. Strikingly, whatever their treatment, a substantial amount of Ce3+ persisted in the anodes, even after operation at 800 C under fuel cell conditions. With hydrogen as fuel, the un-doped and Au-doped Ni-GDC anodes exhibited identical electrochemical performances, comparable to that of much thicker commercial state-of-the-art Ni-GDC anodes. However, under steam reforming conditions with CH4/H2O mixtures the behaviour of the Au-doped Ni-GDC anodes were far superior, exhibiting retention of good power density and dramatically improved resistance to deactivation by carbon deposition. Thus two distinct beneficial effects contributed to overall performance: persistence of Ce3+ in the working anodes could induce a strong metal-support interaction with Ni that enhanced the catalytic oxidation of methane, while formation of a Nisingle bondAu surface alloy that inhibited carbonisation and poisoning of the active nickel surface.
Keywords SOFC; Ultrathin film anodes; Magnetron sputtering; Gadolinia doped ceria; Carbon-tolerant; Gold doping
Remark https://doi.org/10.1016/j.ijhydene.2017.11.020
Link

Electrical properties of polycrystalline materials from the system Cu-As-Ge-Se under high pressure condition

Authors V E Zaikova, N V Melnikova, A V Tebenkov , A A Mirzorakhimov, O P Shchetnikov, A N Babush kin and G V Sukhanova
Source
Journal of Physics: Conference Series
Volume: 917 Time of Publication: 2017
Abstract The paper deals with electrical properties of polycrystalline materials (GeSe)x(CuAsSe2)1-x(x= 0.5 and 0.7) under high pressure (up to 45 GPa) conditions. The phenomenon of negative magnetoresistance was observed for studied materials.
Remark doi :10.1088/1742-6596/917/8/082009
Link

Asymmetric tubular CaTi0.6Fe0.15Mn0.25O3-δ membranes: Membrane architecture and long-term stability

Authors Wen Xing, Marie-Laure Fontaine, Zuoan Li, Jonathan M. Polfus, Yngve Larring, Christelle Denonville, Emmanuel Nonnet, Adam Stevenson, Partow P. Henriksen, Rune Bredesen
Source
Journal of Membrane Science
Volume: 548, Pages: 372-379
Time of Publication: 2018
Abstract Three architectures of asymmetric tubular oxygen transport membranes (OTM) based on CaTi0.6Fe0.15Mn0.25O3-δ were fabricated with various thicknesses of the tubular porous supports and the dense membrane layers. This was achieved by a two-step firing method combining water based extrusion and dip-coating. The oxygen flux of the tubular membranes was characterized as a function of temperature and oxygen partial pressure on both feed and sweep sides for the different architectures. The flux exhibits different functional dependencies with respect to the oxygen partial pressure gradient and the membrane architecture. Numerical simulations using a Dusty-gas model were conducted to evaluate the effect of the porous support microstructure and thickness on oxygen partial pressure gradient inside the porous media. Results from this work were used to establish dependency of the flux with respect to bulk transport properties of the material, surface kinetics and architecture of the porous support. Furthermore, long-term stability of the produced tubular asymmetric membrane operated in CO2-containing atmospheres was assessed over half a year. The membrane exhibited a stable oxygen flux without showing significant flux degradation.
Keywords OTM, Asymmetric tubular membrane, Oxygen flux, CaTiO3, Long-term stability
Remark https://doi.org/10.1016/j.memsci.2017.11.042
Link

Three-dimensional printed yttria-stabilized zirconia self-supported electrolytes for solid oxide fuel cell applications

Authors S.Masciandaro, M. Torrell, P. Leone, A. Tarancn
Source
Journal of the European Ceramic Society
Time of Publication: 2017
Abstract Additive manufacturing represents a revolution due to its unique capabilities for freeform fabrication of near net shapes with strong reduction of waste material and capital cost. These unfair advantages are especially relevant for expensive and energy-demanding manufacturing processes of advanced ceramics such as Yttria-stabilized Zirconia, the state-of-the-art electrolyte in Solid Oxide Fuel Cell applications. In this study, self-supported electrolytes of yttria-stabilized zirconia have been printed by using a stereolithography three-dimensional printer. Printed electrolytes and complete cells fabricated with cathode and anode layers of lanthanum strontium manganite- and nickel oxide-yttria-stabilized zirconia composites, respectively, were electrochemical characterized showing full functionality. In addition, more complex configurations of the electrolyte have been printed yielding an increase of the performance entirely based on geometrical aspects. Complementary, a numerical model has been developed and validated as predictive tool for designing more advanced configurations that will enable highly performing and fully customized devices in the next future.
Keywords Solid oxide fuel cell, 3D printing, Stereolithography, Yttria-stabilized zirconia, Electrolyte
Remark Available online 15 November 2017, https://doi.org/10.1016/j.jeurceramsoc.2017.11.033
Link

Characteristics of LaCo0.4Ni0.6-xCuxO3-δ ceramics as a cathode material for intermediate-temperature solid oxide fuel cells

Authors Yi-XinLiu, Sea-Fue Wang,Yung-Fu Hsu, Hung-Wei Kai, Piotr Jasinski
Source
Journal of the European Ceramic Society
Time of Publication: 2017
Abstract In this study, the effects of Cu-ion substitution on the densification, microstructure, and physical properties of LaCo0.4Ni0.6-xCuxO3-δ ceramics were investigated. The results indicate that doping with Cu ions not only enhances the densification but also promotes the grain growth of LaCo0.4Ni0.6-xCuxO3-δ ceramics. The Cu substitution at x ≤ 0.2 can suppress the formation of La4Ni3O10, while the excess Cu triggers the formation of La2CuO4.032 phase. The p-type conduction of LaCo0.4Ni0.6O3-δ ceramic was significantly raised by Cu substitution because the acceptor doping () triggered the formation of hole carriers; this effect was maximized in the case of LaCo0.4Ni0.4Cu0.2O3-δ composition (1480 S cm−1 at 500 C). Thermogravimetric data revealed a slight weight increase of 0.29% for LaCo0.4Ni0.4Cu0.2O3-δ compact up to 871 C; this is due to the incorporation of oxygen that creates metal vacancies and additional carriers, partially compensating the conductivity loss due to the spin-disorder scattering. As the temperature of the LaCo0.4Ni0.4Cu0.2O3-δ compacts rose above 871 C, significant weight loss with temperature was observed because of the release of lattice oxygen to the ambient air as a result of Co (IV) thermal reduction accompanied by the formation of oxygen vacancies. A solid oxide fuel cell (SOFC) single cell with Sm0.2Ce0.8O2-δ (electrolyte) and LaCo0.4Ni0.4Cu0.2O3-δ (cathode) was built and characterized. The Ohmic (0.256 Ω cm2) and polarization (0.434 Ω cm2) resistances of the single cell at 700 C were determined; and the maximum power density was 0.535 W cm−2. These results show that LaCo0.4Ni0.4Cu0.2O3-δ is a very promising cathode material for SOFC applications.
Keywords Solid oxide fuel cells, Cell performance, Impedance Cathode
Remark Available online 8 November 2017, https://doi.org/10.1016/j.jeurceramsoc.2017.11.019
Link

Influence of processing on stability, microstructure and thermoelectric properties of Ca3Co4 − xO9 + δ

Authors Nikola Kanasac Sathy, Prakash Singh, Magnus Rotan, Mohsin Saleemi, Michael Bittner, Armin Feldhoff, Truls Norby, Kjell Wiika, Tor Grande, Mari-Ann Einarsrud
Source
Journal of the European Ceramic Society
Time of Publication: 2017
Abstract Due to high figure of merit, Ca3Co4 − xO9 + δ (CCO) has potential as p-type material for high-temperature thermoelectrics. Here, the influence of processing including solid state sintering, spark plasma sintering and post-calcination on stability, microstructure and thermoelectric properties is reported. By a new post-calcination approach, single-phase materials were obtained from precursors to final dense ceramics in one step. The highest zT of 0.11 was recorded at 800 C for CCO with 98 and 72% relative densities. In situ high-temperature X-ray diffraction in air and oxygen revealed a higher stability of CCO in oxygen (∼970 C) than in air (∼930 C), with formation of Ca3Co2O6 which also showed high stability in oxygen, even at 1125 C. Since achievement of phase pure high density CCO by post-calcination method in air is challenging, the phase stability of CCO in oxygen is important for understanding and further improvement of the method.
Keywords Ca3Co4 − xO9 + δ, Post calcination, Phase stability, Microstructure, Thermoelectric performance
Remark Available online 6 November 2017, https://doi.org/10.1016/j.jeurceramsoc.2017.11.011
Link

Analysis of potential materials for single component fuel cells

Authors Monica Lin, Ashgar Imran, and Peter Lund
Source
FUNCTIONAL NANOSTRUCTURES PROCEEDINGS
Time of Publication: 2017
Abstract The following paper summarizes the results of systematic analysis on single component fuel cell. This recent technology in the solid oxide fuel cell field consists of a unique layer in place of the conventional three-layers structure. The single layer is a mixture of ionic and semi-conductor material. Surprisingly, the expected short circuit has not shown up. On the contrary, the performance is even higher, as reported in literature [1]. This work aims to compare different combinations of materials in terms of performance. La0.6Sr0.4Co0.2Fe0.8O3-δ(LSCF), LiNi0.8Co0.15Al0.05O2 (NCAL), La0.8Sr0.2CoO3(LSC), LiNiZn oxide (LNZ) and a new kind of material, CuFe2O4 are analysed as semi-conductor material. As ionic conductor, CeO2/Gd (GDC) is mainly tilised. Also, CeO2/Sm (SDC) and CeO2/Sm/Ca SCDC are considered too.
Remark Link

Thermoelectrochemical Heat Converter

Source
Time of Publication: 2017
Abstract A direct thermoelectrochemical heat-to-electricity converter includes two electrochemical cells at hot and cold temperatures, each having a gas-impermeable, electron-blocking membrane capable of transporting an ion I, and a pair of electrodes on opposite sides of the membrane. Two closed-circuit chambers A and B each includes a working fluid, a pump, and a counter-flow heat exchanger. The chambers are connected to opposite sides of the electrochemical cells and carry their respective working fluids between the two cells. The working fluids are each capable of undergoing a reversible redox half-reaction of the general form R→O+I+e−, where R is a reduced form of an active species in a working fluid and O is the oxidized forms of the active species. One of the first pair of electrodes is electrically connected to one the second pair of electrodes via an electrical load to produce electricity. The device thereby operates such that the first electrochemical cell runs a forward redox reaction, gaining entropy, and the second electrochemical cell runs a reverse redox reaction, expelling entropy.
Remark United States Patent Application 20170288253
Link

High-temperature properties of (La,Ca)(Fe,Mg,Mo)O3-δ perovskites as prospective electrode materials for symmetrical SOFC

Authors S.Ya.Istomin, A.V.Morozov, M.M.Abdullayev, M.BatukbJ.Hadermann, S.M.Kazakov, A.V.Sobolev, I.A.Presniakov, E.V.Antipov
Source
Journal of Solid State Chemistry
Volume: 258, Pages: 1-10
Time of Publication: 2018
Abstract La1−yCayFe0.5+x(Mg,Mo)0.5−xO3-δ oxides with the orthorhombic GdFeO3-type perovskite structure have been synthesized at 1573 K. Transmission electron microscopy study for selected samples shows the coexistence of domains of perovskite phases with ordered and disordered B-cations. Mssbauer spectroscopy studies performed at 300 K and 573 K show that while compositions with low Ca-content (La0.55Ca0.45Fe0.5Mg0.2625Mo0.2375O3-δ and La0.5Ca0.5Fe0.6Mg0.175Mo0.225O3-δ) are nearly oxygen stoichiometric, La0.2Ca0.8Fe0.5Mg0.2625Mo0.2375O3-δ is oxygen deficient with δ ≈ 0.15. Oxides are stable in reducing atmosphere (Ar/H2, 8%) at 1173 K for 12 h. No additional phases have been observed at XRPD patterns of all studied perovskites and Ce1−xGdxO2−x/2 electrolyte mixtures treated at 1173–1373K, while Fe-rich compositions (x≥0.1) react with Zr1−xYxO2−x/2 electrolyte above 1273 K. Dilatometry studies reveal that all samples show rather low thermal expansion coefficients (TECs) in air of 11.4–12.7 ppm K−1. In reducing atmosphere their TECs were found to increase up to 12.1–15.4 ppm K−1 due to chemical expansion effect. High-temperature electrical conductivity measurements in air and Ar/H2 atmosphere show that the highest conductivity is observed for Fe- and Ca-rich compositions. Moderate values of electrical conductivity and TEC together with stability towards chemical interaction with typical SOFC electrolytes make novel Fe-containing perovskites promising electrode materials for symmetrical solid oxide fuel cell.
Keywords Symmetrical solid oxide fuel cell, Perovskites, Crystal structure, High-temperature electrical conductivity
Remark https://doi.org/10.1016/j.jssc.2017.10.005
Link

New Solid Electrolyte Na9Al(MoO4)6: Structure and Na+ Ion Conductivity

Authors Aleksandra A. Savina, Vladimir A. Morozov, Anton L. Buzlukov, Irina Yu. Arapova, Sergey Yu. Stefanovich, Yana V. Baklanova, Tatiana A. Denisova, Nadezhda I. Medvedeva, Michel Bardet, Joke Hadermann, Bogdan I. Lazoryak, and
Source
Chem. Mater.
Volume: 29, Issue: 20, Pages: 8901–8913
Time of Publication: 2017
Abstract Solid electrolytes are important materials with a wide range of technological applications. This work reports the crystal structure and electrical properties of a new solid electrolyte Na9Al(MoO4)6. The monoclinic Na9Al(MoO4)6 consists of isolated polyhedral [Al(MoO4)6]9– clusters composed of a central AlO6 octahedron sharing vertices with six MoO4 tetrahedra to form a three-dimensional framework. The AlO6 octahedron also shares edges with one Na1O6 octahedron and two Na2O6 octahedra. Na3–Na5 atoms are located in the framework cavities. The structure is related to that of sodium ion conductor II-Na3Fe2(AsO4)3. High-temperature conductivity measurements revealed that the conductivity (σ) of Na9Al(MoO4)6 at 803 K equals 1.63 10–2 S cm–1. The temperature behavior of the 23Na and 27Al nuclear magnetic resonance spectra and the spin-lattice relaxation rates of the 23Na nuclei indicate the presence of fast Na+ ion diffusion in the studied compound. At T<490 K, diffusion occurs by means of Na+ ion jumps exclusively through the sublattice of Na3–Na5 positions, whereas Na1 and Na2 become involved in the diffusion processes (through chemical exchange with the Na3–Na5 sublattice) only at higher temperatures.
Remark DOI: 10.1021/acs.chemmater.7b03989
Link

Alkali and Alkaline Earth Oxoacid Salts; Synthesis, Hydration, Stability, and Electrical Conductivity

Author AA Elstad
Source
Time of Publication: 2017
Abstract Proton-conducting electrolytes are sough after for use in various applications within the field of electrochemistry. Pure and high proton conductivity has been found in many perovskite-type oxides like BaZrO3 (BZY) and BaCeO3, with BaCeO3-based materials being among the best proton-conducting oxides. In the intermediate temperature range of 400 to 800 C, BZY has been established as one of the most promising materials, exhibiting a protonic conductivity higher than 1  10􀀀2 S cm􀀀1 over the whole temperature range. However, it is difficult to process, and the resulting materials are usually grainy and possess highly resistive grain-boundaries [1]. For low-temperature regions, compounds like CsHSO4 and CsH2PO4 show great potential with respect to protonic conductivity, even displaying superprotonic transitions that immensely increase their conductivity, however their stability is lacking with respect to temperature and solubility in water [2]. With this project, the aim is to broaden the horizon and investigate compounds that fall outside the common perovskite-definition. In this work, various solid acids (E.g. KBaPO4, NaCaHSiO4 and BaH2SiO4), in which the cations are alkali and alkaline earth metals and the anionic groups are separated XO4 tetrahedra, are synthesized and subsequently characterized by X-Ray Diffraction (XRD), Thermogravimetric Analysis (TG), as well as electrical characterization by Impedance Spectroscopy (IS). The work on KBaPO4 culminated in a submitted paper [3]. KBaPO4 has been proposed to transform into a great protonic conductor upon hydration at low temperatures. Effectively, hydration through steam at 80 C is said to give the compound a protonic conductivity of 1  10􀀀2 S cm􀀀1 just below 100 C [4]. This is a remarkable result and, if it can be reproduced, it can become a viable rival to BZY. For this reason, KBaPO4 was chosen as a topic for this work. Here, we synthesize KBaPO4 through a high-temperature solid state reaction, and subsequently characterize the system with respect to thermal stability and its inherent electrical conductivity. Through electrical measurements, we found that the conductivity of pure KBaPO4 was very low, around 2  10􀀀6 S cm􀀀1 at 600 C, with an activation energy exceeding 1 eV. The compound is indifferent to the presence of humidity, and results indicate that the charge carrier in the compound is not protonic, but rather it is theorized to be potassium ions, with potassium Frenkel defects being the predominating defect, however this has not been explicitly confirmed. All in all, we propose a defect model for KBaPO4 with Frenkel defects as the predominating defects. Through attempts at hydrating KBaPO4 in accordance to the method proposed by Goodenough, we found that it does not transform into a high-conductivity phase, but rather decomposes into potassium doped Ba3(PO4)2, and that the resulting system shows similar properties, such as thermal stability (Decomposing at 300 C) and protonic conductivity (1:6  10􀀀6 S cm􀀀1 at 250 C), to the system Ba3-xKxHx(PO4)2 previously investigated by Haile et al. [5], albeit with a significantly lower potassium content than the systems they have characterized, possibly indicating that a saturation of K in Ba3(PO4)2 has been reached. By subsequently heating Ba3-xKxHx(PO4)2 to high temperatures, the system is found to expel potassium and form a two-phase system of Ba3(PO4)2 and a secondary phase of KBaPO4, showing similarities to the system Ba3(1-x)K3x(PO4)2-x previously investigated by Iwahara et al. [6]. Through impedance spectroscopy of said system, we found evidence that points toward the system being a protonic conductor, with a bulk conductivity slightly higher than 1  10􀀀3 S cm􀀀1 at 600 C, and an activation energy of around 0:67 eV. This is one order of magnitude higher than the one previously reported by Iwahara et al., and only one order of magnitude lower than that of BaZrO3. Parallelly, NaCaHSiO4 and related compounds ABHXO4 (A􀀀􀀀 Li, Na or K. B􀀀􀀀 Ca, Sr or Ba. X􀀀􀀀 Si, Ge or Sn) were synthesized hydrothermally and subsequently characterized. Electrical characterization of NaCaHSiO4 gave low conductivities, although protonic, of 1:8  10􀀀8 S cm􀀀1 at 250 C, with an activation energy of 0:9 eV. Based on the results, we propose a defect model in which interstitial hydroxide ions and interstitial protons str significant defects in the compound. However, although NaCaHSiO4 could be successfully synthesized and subsequently characterized, the other syntheses did not yield the desired results. In fact, the only synthesis that yielded a pure product was that which gave Sr2SiO4, possibly providing a hydrothermal approach to synthesizing a compound previously produced by a hightemperature solid state reaction. Lastly, the compound BaH2SiO4 was synthesized, according to a hydrothermal route, and characterized with respect to thermal stability and electrical conductivity. It was found to exhibit a conductivity of 2:5  10􀀀8 S cm􀀀1 at 200 C with an activation energy of 0:88 eV, comparable to that of NaCaHSiO4. Due to BaH2SiO4 showing similar response to various atmospheres as NaCaHSiO4, a defect model containing hydroxide and hydrogen interstitials is proposed for BaH2SiO4 as well. Compared to earlier reports, a discrepancy was found in that the BaH2SiO4 decomposes prior to temperature regions in which data on electrical conductivity has been previously reported. Another, separate investigation into BaH2SiO4 is therefore recommended.
Remark Thesis for the degree of ’Master of Science’, Depertment of Chemistry, University of Oslo
Link

Defect chemistry and electrical properties of BiFeO3

Authors Matthias Schrade, Nahum Mas, Antonio Perejn, Luis A. Prez-Maqueda and Anthony R. West
Source
Journal of Materials Chemistry C
Issue: 38 Time of Publication: 2017
Abstract BiFeO3 attracts considerable attention for its rich functional properties, including room temperature coexistence of magnetic order and ferroelectricity and more recently, the discovery of conduction pathways along ferroelectric domain walls. Here, insights into the defect chemistry and electrical properties of BiFeO3 are obtained by in situ measurements of electrical conductivity, σ, and Seebeck coefficient, α, of undoped, cation-stoichiometric BiFeO3 and acceptor-doped Bi1−xCaxFeO3−δ ceramics as a function of temperature and oxygen partial pressure pO2. Bi1−xCaxFeO3−δ exhibits p-type conduction; the dependencies of σ and α on pO2 show that Ca dopants are compensated mainly by oxygen vacancies. By contrast, undoped BiFeO3 shows a simultaneous increase of σ and α with increasing pO2, indicating intrinsic behavior with electrons and holes as the main defect species in almost equal concentrations. The pO2-dependency of σ and α cannot be described by a single point defect model but instead, is quantitatively described by a combination of intrinsic and acceptor-doped characteristics attributable to parallel conduction pathways through undoped grains and defect-containing domain walls; both contribute to the total charge transport in BiFeO3. Based on this model, we discuss the charge transport mechanism and carrier mobilities of BiFeO3 and show that several previous experimental findings can readily be explained within the proposed model.
Remark Link

Performance and stability in H2S of SrFe0.75Mo0.25O3-δ as electrode in proton ceramic fuel cells

Authors S.Wachowski, M.Polfus, T.Norby
Source
Journal of the European Ceramic Society
Volume: 38, Issue: 1, Pages: 163-171
Time of Publication: 2018
Abstract The H2S-tolerance of SrFe0.75Mo0.25O3-δ (SFM) electrodes has been investigated in symmetric proton ceramic fuel cells (PCFC) with BaZr0.8Ce0.1Y0.1O3-δ (BZCY81) electrolyte. The ionic conductivity of the electrolyte under wet reducing conditions was found to be insignificantly affected in the presence of up to 5000 ppm H2S. The fuel cell exhibited an OCV of about 0.9 V at 700 C, which dropped to about 0.6 V and 0.4 V upon exposure to 500 and 5000 ppm H2S, respectively, on the fuel side. Post characterization of the fuel cell revealed significant degradation of the anode in terms of microstructure and chemical composition due to formation of sulfides such as SrS, MoS2 and Fe3S4. Nevertheless, the fuel cell was still functional due to the sufficient electronic conductivity of some of these sulfides.
Keywords Proton ceramic fuel cells (PCFC), Sulfur tolerance, H2S, Strontium ferrite, Barium zirconate
Remark https://doi.org/10.1016/j.jeurceramsoc.2017.08.020
Link

Improvement of thermoelectric properties of lanthanum cobaltate by Sr and Mn co-substitution

Authors Ashutosh Kumar, D. Sivaprahsam, Ajay D. Thakur
Source
Journal of Alloys and Compounds
Volume: 735, Pages: 1787–1791
Time of Publication: 2017-12
Abstract We report thermoelectric (TE) properties of Sr and Mn co-substituted LaCoO3 system from room temperature to 700 K. Sr-substitutions at La and Mn at Co site in LaCoO3 improves the electrical conductivity (σ). Thermal conductivity (κ) of all the samples increases with the increase in temperature but decreases with the substitution in LaCoO3. An estimation of the electronic thermal conductivity (κe) suggests a dominant phonon contribution to thermal conductivity in this system. A maximum value of the figure of merit is 0.14 at 480 K for La0.95Sr0.05Co0.95Mn0.05O3.
Keywords Seebsys, Powders: solid-state reaction, Thermal conductivity, Electrical conductivity, Perovskites
Remark Link

Fabrication and testing of unileg oxide thermoelectric device

Authors Jyothi Sharma, R. D. Purohit, Deep Prakash, and P. K. Sinha
Source
API Conference Proceedings
Time of Publication: 2017
Abstract A prototype of oxide thermoelectric unileg device was fabricated. This device was based on only n-legs made of La doped calcium manganate. The powder was synthesized, characterised and consolidated in rectangular thermoelements. A 33 device was fabricated by fitting 9 rectangular bars in alumina housing and connected by silver strips. The device has been tested under large temperature difference (ΔT=480C) using an indegenous system. An open circuit voltage of 468 mV was obtained for a nine leg unileg device. The device exhibits a internal resistance of ∼1Ω. The maximum power output for this nine leg device reached upto 50 mW in these working condition
Keywords Seebsys
Remark Link

On the formation of phases and their influence on the thermal stability and thermoelectric properties of nanostructured zinc antimonide

Authors Priyadarshini Balasubramanian, Manjusha Battabyal, Duraiswamy Sivaprahasam and Raghavan Gopalan
Source
Journal of Physics D: Applied Physics
Volume: 50, Issue: 1 Time of Publication: 2016-11
Abstract To investigate the thermal reliability of the structure and thermoelectric properties of the zinc antimony compounds, undoped (Zn4Sb3) and doped (Zn4Sb2.95Sn0.05 and Co0.05Zn3.95Sb3) zinc antimonide samples were processed using the powder metallurgy route. It was observed that the as-prepared undoped sample contains a pure β-Zn4Sb3 phase, whereas the doped samples consist of Ω-ZnSb as the major phase and β-Zn4Sb3 as the minor phase. Differential scanning calorimetry analysis confirms the stability of the β-Zn4Sb3 phase up to 600 K. X-ray diffraction data of the undoped and doped samples show that the nanocrystallinity of the as-prepared samples is retained after one thermal cycle. The thermal bandgap, thermopower and thermal conductivity are not affected by the thermal cycle for the doped samples. A maximum power factor of 0.6 mW m−1 K−2 was achieved in the Sn-doped sample (Zn4Sb2.95Sn0.05). This is enhanced to 0.72 mW m−1 K−2 after one thermal cycle at 650 K under Ar atmosphere and slightly decreases after the third thermal cycle. In the case of the Co-doped sample (Co0.05Zn3.95Sb3), the power factor increases from 0.4 mW m−1 K−2 to 0.7 mW m−1 K−2 after the third thermal cycle. A figure of merit of ~0.3 is achieved at 573 K in the Zn4Sb2.95Sn0.05 sample. The results from the nanoindentation experiment show that Youngs modulus of the Sn-doped sample (Zn4Sb2.95Sn0.05) after the thermal cycle is enhanced (96 GPa) compared to the as-prepared sample (~76 GPa). These important findings on the thermal stability of the thermoelectric and mechanical properties of Sn-doped samples (Zn4Sb2.95Sn0.05) confirm that Sn-doped zinc antimonide samples can be used as efficient thermoelectric materials for device applications.
Keywords Seebsys
Remark Link

The effect of Cu2O nanoparticle dispersion on the thermoelectric properties of n-type skutterudites

Authors M Battabyal, B Priyadarshini, D Sivaprahasam, N S Karthiselva, R Gopalan
Source
Journal of Physics D: Applied Physics
Volume: 48, Issue: 45 Publisher: IOP Publishing Ltd, Time of Publication: 2015-11
Abstract We report the thermoelectric properties of Ba0.4Co4Sb12 and Sn0.4Ba0.4Co4Sb12 skutterudites dispersed with Cu2O nanoparticles. The samples were synthesized by ball milling and consolidated by spark plasma sintering. Dispersion of Cu2O is found to significantly influence the electrical resistivity and thermopower at high temperatures with a more pronounced effect on the electrical resistivity due to the energy filtering effect at the interface between Cu2O nanoparticles and a Ba0.4Co4Sb12 and Sn0.4Ba0.4Co4Sb12 matrix. At 573 K, the electrical resistivity of Ba0.4Co4Sb12 decreases from 5.01    10−5 Ohmm to 2.98    10−5 Ohmm upon dispersion of Cu2O. The dispersion of Cu2O reduces the thermal conductivity of the samples from 300 K and above by increasing the phonon scattering. The lowest observed thermal conductivity at 573 K is found to be 2.001 W mK−1 in Cu2O dispersed Ba0.4Co4Sb12 while it is 2.91 W mK−1 in the Ba0.4Co4Sb12 sample without Cu2O dispersion. Hence Cu2O dispersion plays a significant role in the thermoelectric properties and a maximum figure of merit (ZT ) ~ 0.92 is achieved in Cu2O dispersed Ba0.4Co4Sb12 at 573 K which is more than 200% compared to the pure Ba0.4Co4Sb12 sample. The results from nanoindentation experiments show that the Cu2O dispersed sample (Cu2O  +  Sn0.4Ba0.4Co4Sb11.6) has a higher reduced Youngs modulus (~139 GPa) than the pure Sn0.4Ba0.4Co4Sb11.6 sample (~128 GPa).
Keywords Seebsys
Remark Link

Phase stability and thermoelectric properties of Cu10.5Zn1.5Sb4S13 tetrahedrite

Authors Subramaniam Harisha, Duraisamy Sivaprahasam, Manjusha Battabyal, Raghavan Gopalan
Source
Journal of Alloys and Compounds
Volume: 667, Pages: 323-328
Time of Publication: 2016-05
Abstract Cu10.5Zn1.5Sb4S13 tetrahedrite compound was prepared by mechanical milling of Cu2S, ZnS and Sb2S3 powders and spark plasma sintered (SPS) to dense samples. The phase formation, chemical homogeneity, thermal stability of the compound and the thermoelectric properties of the sintered samples were evaluated. Single phase tetrahedrite with the crystallite size of 40 nm was obtained after 30 h of milling followed by annealing at 573 K for 6 h in an argon atmosphere. In-situ high-temperature X-ray diffraction studies revealed that the phase is stable up to 773 K. The Seebeck coefficient of the sintered samples of density >98% shows p-type behavior with maximum thermopower of 170 μV/K at 573 K. The electrical resistivity (ρ) decreases with temperature up to 475 K and then increases. A low thermal conductivity of 0.5 W/(m⋅K), in combination with moderate power factor gave a maximum ZT of ∼0.038 at 573 K in Cu10.5Zn1.5Sb4S13 sample having a grain size of ∼200 nm.
Keywords Seebsys, Thermoelectric, Tetrahedrite, Solid state reactions, Spark plasma sintering, Figure of merit
Remark Cu10.5Zn1.5Sb4S13
Link

Study of novel proton conductors for high temperature Solid Oxide Cells

Author Anastasia Iakovleva
Source
Time of Publication: 2015
Abstract The main objective of the present work was the systematic study of several groups of materials: Gd3-xMexGaO6-δ (Me = Ca2+, Sr2+), Ba2Y1+xNb1-xO6-δ , and BaZr0.85Y0.15O3-δ (BZY15) as proton conductors. We developed a synthesis route for each group of materials such as microwave- assisted citric acid combustion method, freezedrying synthesis and modified citrate-EDTA complexing method. Pure nanopowders and dense ceramics were obtained after these syntheses plus a classical sintering process. The structure and composition of the obtained products were characterized by X-Ray diffraction (XRD) and scanning electron microscopy (SEM). The temperature dependences of the conductivity were investigated by impedance spectroscopy as a function of pO2 and pH2O. For the family of Gd3-xMexGaO6-δ (Me = Ca2+, Sr2+), we studied the influence of dopant nature and content on the structural and electrical properties. Results indicate that the substitution possible till 10 % of doping content. According to the SEM observations, the grain size is increased with increasing dopant content. Concerning electrical properties, we found an increase of conduction with increasing dopant content. All compounds present a good stability in humid, hydrogen and CO2 containing atmosphere. In case of Ba2Y1+xNb1-xO6-δ materials, the physico-chemical properties of synthesized materials have been characterized by the XRD and SEM techniques. The average grain size increased significantly with increasing amount of Y3+. Conduction properties were slightly improved with the partial substitution of niobium by yttrium. The stability of Ba2Y1+xNb1-xO6-δ compounds was investigated under different atmospheres and conditions. The ionic conduction in this case is quite low, which has been explained by futher molecular dynamics simulations. Finally, we studied the influence of an ZnO and NiO additives on the sintering of BZY15, being these sintering aids used to lower the sintering temperature. Zinc oxide as a sintering aid lowers the sintering temperature by 300 C and slightly increases the bulk and total conductivity of BZY15.
Remark THESE DE DOCTORAT

Advanced low-temperature ceramic nanocomposite fuel cells using ultra high ionic conductivity electrolytes synthesized through freeze-dried method and solid-route

Authors Muhammad Imran Asghar, Mikko Heikkil, Peter D.Lund
Source
Materials Today Energy
Volume: 5, Pages: 338-346
Time of Publication: 2017
Abstract Low ionic conductivity and slow reaction kinetics often limit the performance of a ceramic nanocomposite fuel cell (CNFC). Here, we report a novel synthesis method, freeze-dried method, to achieve a record high ionic conductivity for nanocomposite electrolytes (>0.5 S/cm) based on Ce0.85Sm0.15O2 (SDC) and a eutectic mixture of Na2CO3, Li2CO3, K2CO3 (NLK). The highest ionic conductivity (0.55 S/cm) was reached by increasing the carbonate content of the electrolyte to 35 wt%. For the sake of comparison, the nanocomposite electrolytes were also prepared through solid-route. Composite anodes and cathodes for complete fuels were prepared from NiO and La0.6Sr0.4Co0.2Fe0.8O3 (LSCF), respectively using both solid-route and freeze-dried nanocomposite electrolytes. Complete fuel cells manufactured from these nanocomposite materials produced ∼1.1 W/cm2 at 550 C. The EIS measurements revealed low ohmic losses (0.18 Ω cm2) and even lower charge transfer resistance (0.05 Ω cm2). In addition, it was found that the open-circuit-voltage (OCV) of the CNFCs improved from 1.1 V to 1.2 V when a mixture of air and CO2 was supplied as compared to the case when only air was supplied at the cathode. Finally, high temperature X-ray diffraction (HT-XRD) revealed stable structures of SDC, NiO and LSCF up to 600 C, which shows the thermal stability of these fuel cell materials.
Keywords Fuel cells, Ceramic, Nanocomposite, Carbonate, Ionic conductivity, Perovskite
Remark https://doi.org/10.1016/j.mtener.2017.07.017
Link

Stability and range of the type II Bi1 − xWxO1.5 + 1.5x solid solution

Authors Julia Wind, Paula Kayser, Zhaoming Zhang, Ivana Radosavljevic Evansc, Chris D.Ling
Source
Solid State Ionics
Volume: 308, Pages: 173-180
Time of Publication: 2017
Abstract We have established the stability and range of the cubic type II phase of Bi1 − xWxO1.5 + 1.5x using a combination of X-ray diffraction, neutron diffraction and X-ray absorption spectroscopy. Type II is a high temperature modification that can be obtained by quenching/rapid cooling of samples with compositions between x = 0.148 to x = 0.185. Slower cooling rates yield the stable low temperature polymorph, the tetragonal type Ib phase (Bi rich samples), and mixtures of type Ib and Aurivillius phase (W-rich samples). Throughout the entire solid solution range, type II exhibits a (3 + 3) dimensional incommensurate modulation with modulation vectors slightly smaller than 1/3 based on a cubic fluorite type subcell (δ-Bi2O3). The main structural motifs are well-defined tetrahedra of WO6 octahedra in a δ-Bi2O3-matrix, with additional W being incorporated on corners and face centers of the approximate commensurate 3 3 3 supercell in octahedral coordination, confirmed by XANES analysis of the W L3-edge. Impedance measurements reveal oxide ionic conductivities comparable to those of yttria-stabilised zirconia even after a decrease in ionic conductivity of about half an order of magnitude on thermal cycling due to transition to the tetragonal type Ib phase.
Keywords Oxide ionic conductors, Solid solution, Bismuth oxide, Incommensurately modulated structures, Neutron diffraction, XANES
Remark https://doi.org/10.1016/j.ssi.2017.07.015
Link

High performance novel gadolinium doped ceria/yttria stabilized zirconia/nickel layered and hybrid thin film anodes for application in solid oxide fuel cells

Authors F.J.Garcia-Garcia, A.M. Beltrn, F. Yubero, A.R. Gonzlez-Elipe, R.M. Lambert
Source
Journal of Power Sources
Volume: 363, Pages: 251-259
Time of Publication: 2017
Abstract Magnetron sputtering under oblique angle deposition was used to produce Ni-containing ultra thin film anodes comprising alternating layers of gadolinium doped ceria (GDC) and yttria stabilized zirconia (YSZ) of either 200 nm or 1000 nm thickness. The evolution of film structure from initial deposition, through calcination and final reduction was examined by XRD, SEM, TEM and TOF-SIMS. After subsequent fuel cell usage, the porous columnar architecture of the two-component layered thin film anodes was maintained and their resistance to delamination from the underlying YSZ electrolyte was superior to that of corresponding single component Ni-YSZ and Ni-GDC thin films. Moreover, the fuel cell performance of the 200 nm layered anodes compared favorably with conventional commercially available thick anodes. The observed dependence of fuel cell performance on individual layer thicknesses prompted study of equivalent but more easily fabricated hybrid anodes consisting of simultaneously deposited Ni-GDC and Ni-YSZ, which procedure resulted in exceptionally intimate mixing and interaction of the components. The hybrids exhibited very unusual and favorable IV characteristics, along with exceptionally high power densities at high currents. Their discovery is the principal contribution of the present work.
Keywords Magnetron sputtering, Oblique angle deposition, Thin film anodes, Layered and hybrid structures, SOFC
Remark https://doi.org/10.1016/j.jpowsour.2017.07.085
Link

Relating defect chemistry and electronic transport in the double perovskite Ba1−xGd0.8La0.2+xCo2O6−δ (BGLC)

Authors Einar Vllestad, Matthias Schrade, Julie Segalini, Ragnar Strandbakke, and Truls Norby
Source
Journal of Materials Chemistry A
Volume: 5, Pages: 15743-15751
Time of Publication: 2017
Abstract Rare earth double perovskites comprise a class of functional oxides with interesting physiochemical properties both for low- and high-temperature applications. However, little can be found relating electrical properties with equilibrium thermodynamics of non-stoichiometry and defects. In the present work, a comprehensive and generally applicable defect chemical model is developed to form the link between the defect chemistry and electronic structure of partially substituted BGLC (Ba1−xGd0.8La0.2+xCo2O6−δ, 0 ≤ x ≤ 0.5). The equilibrium oxygen content of 4 different compositions is determined as a function of pO2 and temperature by thermogravimetric analysis, and combined with defect chemical modelling to obtain defect concentrations and thermodynamic parameters. Oxidation enthalpies determined by TG-DSC become increasingly exothermic (−50 to −120 kJ mol−1) with increased temperature and oxygen non-stoichiometry for all compositions, in excellent agreement with the thermodynamic parameters obtained from the defect chemical model. All compositions display high electrical conductivities (500 to 1000 S cm−1) with shallow pO2-dependencies and small and positive Seebeck coefficients (3 to 15 μV K−1), indicating high degree of degeneracy of the electronic charge carriers. The complex electrical properties of BGLC at elevated temperatures is rationalized by a two-band conduction model where highly mobile p-type charge carriers are transported within the valence band, whereas less mobile “n-type” charge carriers are located in narrow Co 3d band.
Remark DOI: 10.1039/C7TA02659E
Link

Formation of NiO/YSZ functional anode layers of solid oxide fuel cells by magnetron sputtering

Authors I.V. Ionov, A.A. Solov’ev, A.M. Lebedinskii, A.V. Shipilova, E.A. Smolyanskii, A N. Koval’chuk, A.L. Lauk
Source
Russian Journal of Electrochemistry
Volume: 53, Issue: 6, Pages: 670–676
Time of Publication: 2017
Abstract The decrease in the polarization resistance of the anode of solid-oxide fuel cells (SOFCs) due to the formation of an additional NiO/(ZrO2 + 10 mol % Y2O3) (YSZ) functional layer was studied. NiO/YSZ films with different NiO contents were deposited by reactive magnetron sputtering of Ni and Zr–Y targets. The elemental and phase composition of the films was adjusted by regulating oxygen flow rate during the sputtering. The resulting films were studied by scanning electron microscopy and X-ray diffractometry. Comparative tests of planar SOFCs with a NiO/YSZ anode support, NiO/YSZ functional nanostructured anode layer, YSZ electrolyte, and La0.6Sr0.4Co0.2Fe0.8O3/Ce0.9Gd0.1O2 (LSCF/CGO) cathode were performed. It was shown that the formation of a NiO/YSZ functional nanostructured anode leads to a 15–25% increase in the maximum power density of fuel cells in the working temperature range 500–800C. The NiO/YSZ nanostructured anode layers lead not only to a reduction of the polarization resistance of the anode, but also to the formation of denser electrolyte films during subsequent magnetron sputtering of electrolyte.
Keywords SOFC, magnetron sputtering, nanostructured electrode, thin-film anode, polarization resistance
Remark Link

Tailoring the electrode-electrolyte interface of Solid Oxide Fuel Cells (SOFC) by laser micro-patterning to improve their electrochemical performance

Authors J.A.Cebollero, R.Lahoz, M.A.Laguna-Bercero, A.Larrea
Source
Journal of Power Sources
Volume: 360, Pages: 336-344
Time of Publication: 2017
Abstract Cathode activation polarisation is one of the main contributions to the losses of a Solid Oxide Fuel Cell. To reduce this loss we use a pulsed laser to modify the surface of yttria stabilized zirconia (YSZ) electrolytes to make a corrugated micro-patterning in the mesoscale. The beam of the laser source, 5 ns pulse width and emitting at λ = 532 nm (green region), is computer-controlled to engrave the selected micro-pattern on the electrolyte surface. Several laser scanning procedures and geometries have been tested. Finally, we engrave a square array with 28 μm of lattice parameter and 7 μm in depth on YSZ plates. With these plates we prepare LSM-YSZ/YSZ/LSM-YSZ symmetrical cells (LSM: La1-xSrxMnO3) and determine their activation polarisation by Electrochemical Impedance Spectroscopy (EIS). To get good electrode-electrolyte contact after sintering it is necessary to use pressure-assisted sintering with low loads (about 5 kPa), which do not modify the electrode microstructure. The decrease in polarisation with respect to an unprocessed cell is about 30%. EIS analysis confirms that the reason for this decrease is an improvement in the activation processes at the electrode-electrolyte interface.
Keywords SOFC, Laser machining, Corrugated surface, Electrode polarisation, Cathode activation, Electrode/electrolyte interface
Remark https://doi.org/10.1016/j.jpowsour.2017.05.106
Link

Suppression of electrical conductivity and switching of conduction mechanisms in ‘stoichiometric’ (Na0.5Bi0.5TiO3)1−x(BiAlO3)x (0 ≤ x ≤ 0.08) solid solutions

Authors Fan Yang, Patrick Wu and Derek C. Sinclair
Source
Journal of Materials Chemistry C
Volume: 5, Pages: 7243-7252
Time of Publication: 2017
Abstract (Na0.5Bi0.5TiO3)1−x(BiAlO3)x (0 ≤ x ≤ 0.08) solid solutions were prepared by a solid state reaction and their electrical properties were established by ac impedance spectroscopy and electromotive force transport number measurements. Incorporation of BiAlO3 (BA) decreases the electrical conductivity of Na0.5Bi0.5TiO3 (NBT) and sequentially changes the conduction mechanism with increasing x from predominant oxide-ion conduction to mixed ionic–electronic conduction and finally to predominant electronic conduction. The suppressed oxide-ion conduction by BA incorporation significantly reduces the dielectric loss at elevated temperatures and produces excellent high-temperature dielectric materials for high BA contents. The possible reasons for the suppressed oxide-ion conduction in the NBT–BA solid solutions have been discussed and we propose that the local structure, especially trapping of oxygen vacancies by Al3+ on the B-site, plays a key role in oxide-ion conduction in these apparently ‘stoichiometric’ NBT-based solid-solution perovskite materials.
Remark DOI: 10.1039/C7TC02519J
Link

High conductive (LiNaK)2CO3Ce0.85Sm0.15O2 electrolyte compositions for IT-SOFC applications

Authors Ieeba Khan, Muhammad Imran Asghar, Peter D.Lund, Suddhasatwa Basu
Source
International Journal of Hydrogen Energy
Volume: 42, Issue: 32, Pages: 20904-20909
Time of Publication: 2017
Abstract Composite electrolytes of lithium, sodium, and potassium carbonate ((LiNaK)2CO3), and samarium doped ceria (SDC) have been synthesized and the carbonate content optimized to study conductivity and its performance in intermediate-temperature solid oxide fuel cell (IT-SOFC). Electrolyte compositions of 20, 25, 30, 35, 45 wt% (LiNaK)2CO3–SDC are fabricated and the physical and electrochemical characterization is carried out using X-ray diffraction, scanning electron microscopy, electrochemical impedance spectroscope, and current–voltage measurements. The ionic conductivity of (LiNaK)2CO3–SDC electrolytes increases with increasing carbonate content. The best ionic conductivity is obtained for 45 wt% (LiNaK)2CO3–SDC composite electrolyte (0.72 S cm−1 at 600 C) followed by the 35 wt% (LiNaK)2CO3–SDC composite electrolyte (0.55 S cm−1 at 600 C). The symmetrical cell of the 35 wt% (LiNaK)2CO3–SDC composite electrolyte with lanthanum strontium cobalt ferrite (LSCF) electrode in air gives an area specific resistance of 0.155 Ω cm2 at 500 C. The maximum power density of the fuel cell using 35 wt% (LiNaK)2CO3–SDC composite electrolyte, composite NiO anode and composite LSCF cathode is found to be 801 mW cm−2 at 550 C.
Keywords IT-SOFC, Ternary carbonate–SDC electrolyte, Carbonate loading, Composite electrolytes
Remark https://doi.org/10.1016/j.ijhydene.2017.05.152
Link

Mixed ionic–electronic conduction in K1/2Bi1/2TiO3

Authors Linhao Li, Ming Li, Ian M. Reaney and Derek C. Sinclair
Source
J. Mater. Chem. C
Volume: 5, Pages: 6300-6310
Time of Publication: 2017
Abstract Recently, it has been reported that the Pb-free piezoelectric perovskite Na1/2Bi1/2TiO3 (NBT) can be compositionally tuned by close control of the A-site starting stoichiometry to exhibit high levels of oxide-ion conduction. The related K1/2Bi1/2TiO3 (KBT) perovskite has also drawn considerable interest as a promising Pb-free piezoelectric material; however, its conduction properties have been less extensively investigated. Here we report on the influence of the K/Bi ratio in the starting composition on the electrical properties using a combination of impedance spectroscopy and ion-transport property measurements. KBT ceramics exhibit mixed ionic–electronic (oxide-ion) conduction with tion ∼ 0.5 at 600–800 C and although variations in the A-site starting stoichiometry can create a ∼1 order of magnitude difference in the bulk conductivity at >500 C, the conductivity is low (ca. 0.1 to 1 mS cm−1 at 700 C) and the activation energy for bulk conduction remains in the range ∼1.2 to 1.5 eV. The high temperature electrical transport properties of KBT are therefore much less sensitive to the starting A-site stoichiometry as compared to NBT. However, KBT ceramics exhibit non-negligible proton conduction at lower temperatures (<300 C). For K/Bi ≥ 1 the total conductivity of KBT ceramics at room temperature can be as high as ∼0.1 mS cm−1 under wet atmospheric conditions. This study demonstrates ionic conduction to be a common feature in A1/2Bi1/2TiO3 perovskites, where A = Na, K.
Remark DOI: 10.1039/C7TC01786C
Link

Effect of plasma spraying power on LSGM electrolyte of metal-supported solid oxide fuel cells

Authors Chang-Sing Hwang, Te-Jung Hwang, Chun-Huang Tsai, Chun-Liang Chang, Sheng-Fu Yang, Ming-Hsiu Wu, Cheng-Yun Fu
Source
Ceramics International
Volume: 43, Issue: 1, Pages: S591-S597
Time of Publication: 2017
Abstract Four nickel-iron metal-supported solid oxide fuel cells with a diameter of 2.4 cm and a cathode active area of 1.76 cm2 are fabricated by atmospheric plasma spraying (APS) and heat-treated in air at 850 C and 500 g cm−2 pressure for 4 h. These cells with the same functional layer materials have electrolyte layers produced by different APS torch powers, but the APS fabrication parameters for other functional layers of these cells are kept the same. XRD data show that there is a LaSrGaO4 impurity phase in the prepared dense LSGM electrolyte produced at 54 kW torch power. According to experimental data on the current-voltage-power and AC impedance measurements at temperatures ranging from 550 to 800 C, the cell with dense LSGM electrolyte produced at 52 kW torch power has the best power performance and the lowest electrolyte resistance and the corresponding delivered power densities at 0.7 V for 550, 600, 650, 700, 750 and 800 C temperatures are 0.147, 0.271, 0.426, 0.585, 0.716 and 0.796 W cm−2, respectively.
Keywords Metal-supported, Solid oxide fuel cell, Atmospheric plasma spraying, LSGM electrolyte
Remark Link

Composite mixed ionic-electronic conducting ceramic for intermediate temperature oxygen transport membrane

Authors Ming Wei Liao, Tai Nan Lin, Wei Xin Kao, Chun Yen Yeh, Yu Ming Chen, Hong Yi Kuo
Source
Ceramics International
Volume: 43, Issue: 1, Pages: S628-S632
Time of Publication: 2017
Abstract The dense ceramic substrate formed by a mixed ionic-electronic conducting (MIEC) material can be used as an oxygen transport membrane (OTM), enabling the transport of high flux oxygen with certain selectivity and gas separation at high temperatures (800 ~ 900 C). In recent years, Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) has been reported to be a promising MIEC material for oxygen permeation due to its relatively high oxygen ion conductivity at high temperatures. However, the catalytic efficiency of BSCF is relatively low among the MIEC materials, resulting in the dramatic decrease of oxygen permeation at temperatures below 800 C. In the present study, a composite MIEC ceramic consisting of a BSCF substrate and the catalytic La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) layer has been proposed. A simple method of laser surface melting is executed to fabricate the composite oxygen transport membrane. The scanning electron microscope (SEM) investigations show that LSCF powders can be well-adherent to the BSCF surface after laser scanning melting process. The oxygen permeation flux reaches 0.5 ml min−1 cm−2 for pure BSCF membrane with thickness of 420 m, while the BSCF membrane substrate with laser scanning LSCF exhibits substantial improvement on oxygen permeation up to 60% at 700 C. The result suggests that the composite MIEC ceramic has significant potential for intermediate temperature oxygen transport membrane.
Keywords Membranes, Composites, Laser surface melting
Remark https://doi.org/10.1016/j.ceramint.2017.05.222
Link

The Effect of Metallic Co-Coating Thickness on Ferritic Stainless Steels Intended for Use as Interconnect Material in Intermediate Temperature Solid Oxide Fuel Cells

Authors Hannes Falk-Windisch, Julien Claquesin, Jan-Erik Svensson, Jan Froitzheim
Source
Oxidation of Metals
Pages: 1–18
Time of Publication: 2017
Abstract The effect of metallic Co-coating thickness on ferritic stainless steels is investigated. This material is suggested to be used as interconnect material in intermediate temperature solid oxide fuel cells. Uncoated, 200-, 600-, 1000-, and 1500-nm Co-coated Sanergy HT is isothermally exposed for up to 500 h in air at 650 C. Mass gain is recorded to follow oxidation kinetics, and area-specific resistance (ASR) measurements are conducted on samples exposed for 168 and 500 h. The microstructure of the thermally grown oxide scales is characterized utilizing scanning electron microscopy and energy-dispersive X-ray analysis on broad ion beam-milled cross sections. A clear increase in ASR as a function of Co-coating thickness is observed. However, the increase in ASR, as an effect of a thicker Co-coating, is correlated with thicker (Cr,Fe)2O3 scales formed on these materials and not to an increase in Co spinel top layer thickness.
Keywords Solid oxide fuel cell, Interconnect, Coating, Area-specific resistance, Corrosion
Remark DOI 10.1007/s11085-017-9782-9
Link

Porous Ca3Co4O9 with enhanced thermoelectric properties derived from Sol–Gel synthesis

Authors Michael Bittner, Lailah Helmich, Frederik Nietschke, Benjamin Geppert, Oliver Oeckler, Armin Feldhoff
Source
Journal of the European Ceramic Society
Time of Publication: 2017
Abstract Highly porous Ca3Co4O9 thermoelectric oxide ceramics for high-temperature application were fabricated by sol–gel synthesis and subsequent conventional sintering. Growth mechanism of misfit-layered Ca3Co4O9 phase, from sol–gel synthesis educts and upcoming intermediates, was characterized by in-situ X-ray diffraction, scanning electron microscopy and transmission electron microscopy investigations. The Ca3Co4O9 ceramic exhibits a relative density of 67.7%. Thermoelectric properties were measured from 373 K to 1073 K. At 1073 K a power factor of 2.46 μW cm−1 K−2, a very low heat conductivity of 0.63 W m−1 K−1 and entropy conductivity of 0.61 mW m−1 K−2 were achieved. The maintained figure of merit ZT of 0.4 from sol–gel synthesized Ca3Co4O9 is the highest obtained from conventional, non-doped Ca3Co4O9. The high porosity and consequently reduced thermal conductivity leads to a high ZT value.
Keywords Thermoelectricity; Thermal conductivity; Porosity; Oxide; Ca3Co4O9
Remark https://doi.org/10.1016/j.jeurceramsoc.2017.04.059
Link

Electrochemical performance of Co3O4/CeO2 electrodes in H2S/H2O atmospheres in a proton-conducting ceramic symmetrical cell with BaZr0.7Ce0.2Y0.1O3 solid electrolyte

Authors Tz. Kraia, S. Wachowski, E. Vllestad, R. Strandbakke, M. Konsolakis, T. Norby, G.E. Marnellos
Source
Solid State Ionics
Time of Publication: 2017
Abstract The electrochemical performance of Co3O4/CeO2 mixed oxide materials as electrodes, when exposed to H2S/H2O atmospheres, was examined employing a proton conducting symmetrical cell, with BaZr0.7Ce0.2Y0.1O3 (BZCY72) as the solid electrolyte. The impact of temperature (700–850 C) and H2S concentration (0–1 v/v%) in steam-rich atmospheres (90 v/v% H2O) on the overall cell performance was thoroughly assessed by means of electrochemical impedance spectroscopy (EIS) studies. The performance of the Co3O4/CeO2 electrode was significantly enhanced by increasing the H2S concentration and temperature. The obtained results were interpreted on the basis of EIS results and physicochemical characterization (XRD, SEM) studies of fresh and used electrodes. Notably, it was found that the mass transport processes, mainly associated with the adsorption and diffusion of the intermediate species resulting by the chemical and half-cell reactions taking place during cell operation, dominate the electrode polarization resistance compared with the charge transfer processes. Upon increasing temperature and H2S concentration, the electrode resistance is substantially lowered, due to the in situ activation and morphological modifications of the electrode, induced by its interaction with the reactants (H2S/H2O) and products (H2/SO2) mixtures.
Keywords H2S-tolerant electrodes; Cobalt-ceria oxides; BZCY72
Remark https://doi.org/10.1016/j.ssi.2017.04.010
Link

Thermal stability and enhanced thermoelectric properties of the tetragonal tungsten bronzes Nb8−xW9+xO47 (0 < x < 5)

Authors G. Cerretti, M. Schrade, X. Song, B. Balke, H. Lu, T. Weidner, I. Lieberwirth, M. Panthfer, T. Norby and W. Tremel
Source
Journal of Materials Chemistry A
Time of Publication: 2017
Abstract Thermoelectric materials are believed to play a fundamental role in the energy field over the next years thanks to their ability of directly converting heat into usable electric energy. To increase their integration in the commercial markets, improvements of the efficiencies are needed. At the same time, cheap and non-toxic materials are required along with easily upscalable production cycles. Compounds of the tetragonal tungsten bronze (TTB) series Nb8−xW9+xO47 fulfill all these requirements and are promising materials. Their adaptive structure ensures glass-like values of the thermal conductivity, and the substitution on the cation side allows a controlled manipulation of the electronic properties. In this contribution we report the stability study of the two highly substituted samples of the series, Nb5W12O47 (x = 3) and Nb4W13O47 (x = 4), when subjected to thermal cycling. Moreover, we show the results of the thermoelectric characterization of these samples. The two compounds have not been affected by the thermal treatment and showed an improvement of the thermoelectric performances up to a zT = 0.2 above 1000 K.
Remark Link

Influence of (Zn,Co)O/ZnO) interface amounts on ionic conduction performance of (Zn1-x,Cox)O (x=0.01, 0.05 and 0.10)

Authors Shalima Shawuti, Musa Mutlu Can, Mehmet Ali Glgn, Satoru Kaneko, Endo Tamio
Source
Composites Part B: Engineering
Time of Publication: 2017
Abstract We investigated the effect of dopant Co atoms into ZnO lattice, on ionic conduction at internal grain and/or through the grain boundary. Influence of dopant Co amount on resistivity was associated with enhanced activation energies of ionic conductivity through the grain boundaries. The change in the activation energy indicated that the mechanism of ionic conduction through the boundaries can be manipulated with Co amount in the lattice. Three conductance mechanisms were identified from the Cole-Cole Plots in order to understand the relaxation mechanism and activation energies of ionic transportations. Formed activation energy, 395 meV, by increasing Co dopant amount up to 10 mol% was attributed to enhanced ionic conductivity through enhancing (Zn,Co)O/ZnO) interface amounts at the grain boundaries. Furthermore, increased activation energy were also enhanced the electronic stability at high temperatures due to decrease in electronic conductivity compared to undoped ZnO.
Keywords Ionic activation energy; Oxide semiconductors; Impedance spectroscopy
Remark https://doi.org/10.1016/j.compositesb.2017.04.020
Link

Development of novel metal-supported proton ceramic electrolyser cell with thin film BZY15–Ni electrode and BZY15 electrolyte

Authors M. Stange, E. Stefan, C. Denonville, Y. Larring, P.M. Rrvik, R. Haugsrud
Source
International Journal of Hydrogen Energy
Volume: 42, Issue: 19, Pages: 13454–13462
Time of Publication: 2017
Abstract Metal supports for planar MS-PCEC were manufactured using tape-casting of low-cost ferritic stainless steel. A coating protecting the metal support against oxidation was applied by vacuum infiltration and a buffer layer of La0.5Sr0.5Ti0.75Ni0.25O3–δ (LSTN) was further deposited to smoothen the surface. The BaZr0.85Y0.15O3–δ–NiO (BZY15–NiO) cathode and the BaZr0.85Y0.15O3–δ (BZY15) electrolyte were applied by pulsed laser deposition (PLD) at elevated substrate temperatures (at 700 C and 600 C, respectively). The main challenges are related to the restrictions in sintering temperature and atmosphere induced by the metal support, as well as strict demands on the roughness of substrates used for PLD. Reduction treatment of the half cells confirmed that NiO in the BZY15–NiO layer was reduced to Ni, resulting in increased porosity of the BZY15–Ni cathode, while keeping the columnar and dense microstructure of the BZY15 electrolyte. Initial electrochemical testing with a Pt anode showed a total resistance of 40 Ωcm2 at 600 C. Through this work important advances in using metal supports and thin films in planar PCEC assemblies have been made.
Keywords Proton ceramic electrolyser cell (PCEC); Tape casting; Thin film deposition; Metal supports
Remark https://doi.org/10.1016/j.ijhydene.2017.03.028
Link

Energetically benign synthesis of lanthanum silicate through “silica garden” route and its characterization

Authors Kavita Parmar, Santanu Bhattacharjee
Source
Materials Chemistry and Physics
Volume: 194, Pages: 147–152
Time of Publication: 2017
Abstract Lanthanum silicate synthesis through “silica garden” route has been reported as an alternative to energy intensive milling procedure. Under optimum conditions lanthanum chloride crystals react with water glass (sodium silicate) to produce self generating hollow lanthanum silicate precipitation tube(s) (LaSPT). The micro tubes are irregular, thick, white coloured and amorphous but are hierarchically built from smaller tubules of 10–20 nm diameters. They retain their amorphous nature on being heated up to 600 C beyond which crystallization starts. The major phase in the LaSPT heated at 900 C is La2Si2O7. “As synthesized” LaSPT is heterogeneous and comprises non stoichiometric phases. The exterior and interior surfaces of these tubes are remarkably different in their morphology and chemical composition. LaSPT sintered at 1200 and 1300 C show fair amount of ionic conductivity.
Keywords Silica garden; Lanthanum silicate; Synthesis; Characterization
Remark https://doi.org/10.1016/j.matchemphys.2017.03.021
Link

Effect of Pt catalyst and external circuit on the hydrogen permeation of Mo and Nb co-doped lanthanum tungstate

Authors Yong Cao, Bo Chi, Jian Pu, Li Jian
Source
Journal of Membrane Science
Volume: 553, Pages: 336–341
Time of Publication: 2017
Abstract In this contribution, the hydrogen permeation properties of 30% Mo and 15% Nb co-doped La5.4WO11.1-δ (LWNM30) with/without Pt catalyst and external circuit were investigated. It was found that the surface reaction was the limiting factor in the hydrogen permeation process of LWNM30, and could be improved by using Pt as catalyst. The applied external circuit could also increase the hydrogen flux of LWNM30, and two followed effects might be responsible: the external circuit could transfer the electrons and promote the diffusion process; the external circuit could remove the charge layer on the surface and enhance the surface reaction rate.
Keywords Lanthanum tungstate; Hydrogen permeation; Pt catalyst; Mo and Nb; External circuit
Remark Link

Magnetron-sputtered La0.6Sr0.4Co0.2Fe0.8O3 nanocomposite interlayer for solid oxide fuel cells

Authors A. A. Solovyev, I. V. Ionov, A. V. Shipilova, A. N. Kovalchuk, M. S. Syrtanov
Source
Journal of Nanoparticle Research
Time of Publication: 2017
Abstract A thin layer of a La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) is deposited between the electrolyte and the La0.6Sr0.4Co0.2Fe0.8O3/Ce0.9Gd0.1O2 (LSCF/CGO) cathode layer of a solid oxide fuel cell (SOFC) by pulsed magnetron sputtering using an oxide target of LSCF. The films were completely dense and well adherent to the substrate. The effects of annealing in temperature range from 200 to 1000 C on the crystalline structure of the LSCF films have been studied. The films of nominal thickness, 250–500 nm, are crystalline when annealed at temperatures above 600 C. The crystalline structure, surface topology, and morphology of the films were determined using X-ray diffraction (XRD), atomic force microscopy (AFM), and scanning electron microscopy (SEM), respectively. To study the electrochemical characteristics of the deposited-film, solid oxide fuel cells using 325-nm LSCF films as interlayer between the electrolyte and the cathode have been fabricated. The LSCF interlayer improves the overall performance of the SOFC by increasing the interfacial area between the electrolyte and cathode. The electrolyte-supported cells with the interlayer have 30% greater, overall power output compared to that achieved with the cells without interlayer. The LSCF interlayer could also act as a transition layer that improves adhesion and relieves both thermal stress and lattice strain between the cathode and the electrolyte. Our results demonstrate that pulsed magnetron sputtering provides a low-temperature synthesis route for realizing ultrathin nanocrystalline LSCF film layers for intermediate- or low-temperature solid oxide fuel cells.
Keywords (La,Sr)(Co,Fe)O3 Magnetron sputtering Nanocomposite Interlayer Solid oxide fuel cells Nanostructured thin films Energy conversion
Remark DOI: 10.1007/s11051-017-3791-0
Link

Ferroelectric crystal Ca9Yb(VO4)7 in the series of Ca9R(VO4)7 non-linear optical materials (R = REE, Bi, Y)

Authors Bogdan I. Lazoryak, Sergey M. Aksenov, Sergey Yu. Stefanovich, Nikolai G. Dorbakov, Dmitriy A. Belov, Oksana V. Baryshnikova, Vladimir A. Morozov, Mikhail S. Manylov and Zhoubin Lin
Source
Journal of Materials Chemistry C
Time of Publication: 2017
Abstract The crystal structure, thermal, dielectric and second harmonic generation (SHG), and nonlinear optical activity data for whitlockite-type Ca9Yb(VO4)7 single crystals were obtained on one and the same sample produced by means of the Czochralski method. The crystal structure refinement has revealed that Yb3+ cations substitute for Ca2+ ions only in the M1, M2 and M5 positions of the whitlockite-type structure. Dielectric, differential thermal analysis and SHG data have shown that Ca9Yb(VO4)7 belongs to the family of high-temperature Ca3(VO4)2 ferroelectrics with Curie temperature Tc = 1221 K, where the symmetry changes from R3c to R[3 with combining macron]c. At higher temperatures a previously unknown complementary phase transition is discovered at T2 = 1276 K and is associated with the symmetry change during heating from R[3 with combining macron]c to R[3 with combining macron]m. Unlike other whitlockites, two phase transitions in Ca9Yb(VO4)7 are separated by a broad interval (ΔT = 55 K) which allows one to register two phase transitions by DSC and dielectric measurements. According to the thermal type both transitions are classified as first-order transformations and their structural mechanisms are considered. Inhomogeneity in the cation distribution is argued to have a crucial influence on the optical quality and ferroelectric domain structures of Ca9Yb(VO4)7 and other whitlockite-type laser crystals.
Remark Link

Status report on high temperature fuel cells in Poland – Recent advances and achievements

Authors J. Molenda, J. Kupecki, R. Baron, M. Blesznowski, G. Brus, T. Brylewski, M. Bucko, J. Chmielowiec, K. Cwieka, M. Gazda, A. Gil, P. Jasinski, Z. Jaworski, J. Karczewski, M. Kawalec, R. Kluczowski, M. Krauz, F. Krok, B. Lukasik, M. Malys, A. Mazur, A. Miele
Source
International Journal of Hydrogen Energy
Volume: 42, Issue: 7, Pages: 4366–4403
Time of Publication: 2017
Abstract The paper presents recent advances in Poland in the field of high temperature fuel cells. The achievements in the materials development, manufacturing of advanced cells, new fabrication techniques, modified electrodes and electrolytes and applications are presented. The work of the Polish teams active in the field of solid oxide fuel cells (SOFC) and molten carbonate fuel cell (MCFC) is presented and discussed. The review is oriented towards presenting key achievements in the technology at the scale from microstructure up to a complete power system based on electrochemical fuel oxidation. National efforts are covering wide range of aspects both in the fundamental research and the applied research. The review present the areas of (i) novel materials for SOFC including ZrO2-based electrolytes, CeO2-based electrolytes, Bi2O3 based electrolytes and proton conducting electrolytes, (ii) cathode materials including thermal shock resistant composite cathode material and silver-containing composites, (iii) anode materials, (iv) metallic interconnects for SOFC, (v) novel fabrication techniques, (vi) pilot scale SOFC, including electrolyte supported SOFC (ES-SOFC) and anode supported SOFC (AS-SOFC), (vii) metallic supported SOFC (MS-SOFC), (viii) direct carbon SOFC (DC-SOFC), (ix) selected application of SOFC, (x) advances in MCFC and their applications, (xi) advances in numerical methods for simulation and optimization of electrochemical systems.
Keywords SOFC; MCFC; Experiments; Simulations; Fabrication techniques
Remark https://doi.org/10.1016/j.ijhydene.2016.12.087
Link

Surface Protonics Promotes Catalysis

Authors R. Manabe, S. Okada, R. Inagaki, K. Oshima, S. Ogo & Y. Sekine
Source
Nature Scientific Reports
Volume: 6, Pages: Article number: 38007
Time of Publication: 2016
Abstract Catalytic steam reforming of methane for hydrogen production proceeds even at 473 K over 1 wt% Pd/CeO2 catalyst in an electric field, thanks to the surface protonics. Kinetic analyses demonstrated the synergetic effect between catalytic reaction and electric field, revealing strengthened water pressure dependence of the reaction rate when applying an electric field, with one-third the apparent activation energy at the lower reaction temperature range. Operando–IR measurements revealed that proton conduction via adsorbed water on the catalyst surface occurred during electric field application. Methane was activated by proton collision at the Pd–CeO2 interface, based on the inverse kinetic isotope effect. Proton conduction on the catalyst surface plays an important role in methane activation at low temperature. This report is the first describing promotion of the catalytic reaction by surface protonics.
Keywords Catalytic mechanisms, Energy, Heterogeneous catalysis, Surface spectroscopy
Remark doi:10.1038/srep38007
Link

Sm6-xMoO12-δ (x = 0, 0.5) and Sm6WO12 – Mixed electron-proton conducting materials

Authors A.V. Shlyakhtina, S.N. Savvin, N.V. Lyskov, D.A. Belov, A.N. Shchegolikhin, I.V. Kolbanev, O.K. Karyagina, S.A. Chernyak, L.G. Shcherbakova, P. Nez
Source
Solid State Ionics
Time of Publication: 2017
Abstract Samarium molybdates Sm6-xMoO12-δ (x = 0, 0.5) and samarium tungstate Sm6WO12 – potential mixed electron-proton conductors have been studied by X-ray diffraction, Raman spectroscopy, SEM and impedance spectroscopy (in ambient air and in dry and wet air). Solid solutions differing in structure have been obtained in the Sm2O3-MoO3 system at 1600 C. The samarium molybdate Sm6MoO12 has the fluorite structure (Fm3m). The less samarium rich solid solution Sm5.5MoO11.25 crystallizes in a rhombohedral (View the MathML sourceR3) structure. The morphotropic transformation is due to the change in the chemical composition of the solid solution with decreasing Sm3 + concentration. The total conductivity of the cubic fluorite phase Sm6MoO12 at 750 C in air (1.48 10− 3 S/cm, Ea = 1.22 eV) is an order of magnitude higher than that of rhombohedral Sm5.5MoO11.25 (2.34 10− 4 S/cm, Ea = 1.11 eV). At low temperatures (T < 500 C), the Arrhenius plot of total conductivity for Sm6MoO12 and Sm5.5MoO11.25 in air deviates from linearity, suggesting that there is a proton contribution to its conductivity at these temperatures, like in the case of the Sm5.4Zr0.6MoO12.3 zirconium-doped molybdate. Below ~ 500 C, Sm6MoO12 fluorite and fluorite-like Sm6WO12 have identical Arrhenius plots of conductivity in ambient air. The region of dominant proton conductivity is wider for Sm6WO12 than Sm6MoO12, reaching temperatures as high as 750 С for the former. The absolute values of total conductivity obtained for samarium tungstate and molybdate at 400 С in wet air are virtually identical and close to 3 10− 6 S/cm, which suggests the conductivity of both compounds is dominated by protons at low temperatures and the proton transport numbers are similar.
Keywords Phase transition; Fluorite; Fluorite-like phase; Proton-conducting membranes; Proton conductivity; Electron conductivity
Remark http://dx.doi.org/10.1016/j.ssi.2017.01.020
Link

The effect of Zr-substitution in La1‐xSrxCo0.2M0.6Zr0.2O3‐δ (M = Fe, Mn) on the crystal structure, thermal expansion and electronic transport properties

Authors Vegar ygarden, Tor Grande
Source
Solid State Ionics
Volume: 301, Pages: 53–58
Time of Publication: 2017
Abstract The effect of Zr-substitution on the evolution of crystal structure, thermal expansion and the electronic transport properties is reported for La1‐xSrxCo0.2Fe0.6Zr0.2O3‐δ (0.1 ≤ x ≤ 1.0) and La1‐xSrxCo0.2Mn0.6Zr0.2O3-δ (x = 0.1, 0.2, 0.25, 0.3). La1‐xSrxCo0.2Fe0.6Zr0.2O3‐δ was found to be single-phase for the compositions investigated. The electrical conductivity of La1‐xSrxCo0.2Fe0.6Zr0.2O3‐δ demonstrated a maximum for x = 0.5, while the area specific resistance was shown to decrease significantly with increasing Sr-content due to an increased concentration of oxygen vacancies. No signs of oxygen vacancy ordering were observed. The area specific resistance of La0.3Sr0.7Co0.2Fe0.6Zr0.2O3‐δ at 600 C is close to an order of magnitude lower than reported values for La0.4Sr0.6Co0.2Fe0.8O3‐δ. The series La1‐xSrxCo0.2Mn0.6Zr0.2O3‐δ was found as multiphase materials. The stability of both series is discussed with respect to the red-ox properties of the transition metals.
Keywords Perovskite; Zr-substitution; X-ray diffraction; Electrical conductivity; Thermal expansion
Remark http://dx.doi.org/10.1016/j.ssi.2017.01.011
Link

Co- and Ce/Co-coated ferritic stainless steel as interconnect material for Intermediate Temperature Solid Oxide Fuel Cells

Authors Hannes Falk-Windisch, , Julien Claquesin, Mohammad Sattari, Jan-Erik Svensson, Jan Froitzheim
Source
Journal of Power Sources
Volume: 343, Pages: 1-10
Time of Publication: 2017
Abstract Chromium species volatilization, oxide scale growth, and electrical scale resistance were studied at 650 and 750 C for thin metallic Co- and Ce/Co-coated steels intended to be utilized as the interconnect material in Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFC). Mass gain was recorded to follow oxidation kinetics, chromium evaporation was measured using the denuder technique and Area Specific Resistance (ASR) measurements were carried out on 500 h pre-exposed samples. The microstructure of thermally grown oxide scales was characterized using Scanning Electron Microscopy (SEM), Scanning Transmission Electron Microscopy (STEM), and Energy Dispersive X-Ray Analysis (EDX). The findings of this study show that a decrease in temperature not only leads to thinner oxide scales and less Cr vaporization but also to a significant change in the chemical composition of the oxide scale. Very low ASR values (below 10 mΩ cm2) were measured for both Co- and Ce/Co-coated steel at 650 and 750 C, indicating that the observed change in the chemical composition of the Co spinel does not have any noticeable influence on the ASR. Instead it is suggested that the Cr2O3 scale is expected to be the main contributor to the ASR, even at temperatures as low as 650 C.
Keywords Interconnect; Solid oxide fuel cell; Corrosion; Cr vaporization; Area specific resistance; Coating
Remark http://dx.doi.org/10.1016/j.jpowsour.2017.01.045
Link

Characterization of laser-processed thin ceramic membranes for electrolyte-supported solid oxide fuel cells

Authors J.A. Cebollero, R. Lahoz, M.A. Laguna-Bercero, J.I. Pea, A. Larrea, V.M. Orera
Source
International Journal of Hydrogen Energy
Time of Publication: 2017
Abstract By laser machining we have prepared thin and self-supported yttria stabilized zirconia (YSZ) electrolytes that can be used in electrolyte-supported solid oxide fuel cells for reducing the operation temperature. The membranes, which are supported by thicker areas of the same material, have an active area of ∼20 μm in thickness and up to 8 mm in diameter. Buckling limits the maximum size of the thin areas to below 1 mm, the overall effective active area being formed by multiple thin areas bounded by ribs. Electron Backscattering Diffraction experiments determined that there are not significant strains inside the membranes and that the heat-affected zone is confined to a shallow layer of ∼1–2 μm. The bending strength of the membranes decreases by ∼26% as a result of the surface microcracking produced by the laser machining. The membranes have a roughness of ∼2.5 μm and are coated by a layer of nanoparticles produced by the laser ablation. This coating and small roughness is not detrimental for the cathodic polarization of the cells. Conversely, the cathode polarization resistance decreases ∼5% in the 650–850 C temperature range.
Keywords SOFC; Solid electrolytes; Laser machining; Self-supporting ceramic membranes
Remark http://dx.doi.org/10.1016/j.ijhydene.2016.12.112
Link

Tuning of nonlinear optical and ferroelectric properties via the cationic composition of Ca9.5–1.5xBixCd(VO4)7 solid solutions

Authors N.G. Dorbakov, O.V. Baryshnikova, V.A. Morozov, A.A. Belik, Y. Katsuya, M. Tanaka, S.Yu. Stefanovich, B.I. Lazoryak
Source
Materials & Design
Volume: 116, Pages: 515–523
Time of Publication: 2017
Abstract Ca9.5–1.5xBixCd(VO4)7 (0 ≤ x ≤ 1) solid solutions with the whitlockite-type structure (SG R3c) were synthesized by a standard solid-state method in air. Structures of Ca9.5–1.5xBixCd(VO4)7 (x = 0.167, 0.5, 0.833) were refined by the Rietveld method from synchrotron powder X-ray diffraction data. Nonlinear optical properties of the whitlockite-type compounds can be designed and increased by an order of magnitude through appropriate isovalent and aliovalent substitutions for Ca2+ cations. Dielectric and temperature second harmonic generation investigations revealed the presence of a reversible ferroelectric phase transition in the range from 1331 K to 1055 K. The phase transition temperature monotonically decreases while nonlinear optical activity of Ca9.5–1.5xBixCd(VO4)7 strongly increases with increasing Bi3+ content.
Keywords Vanadates; Ferroelectric properties; Nonlinear optical properties; Crystal structure
Remark http://dx.doi.org/10.1016/j.matdes.2016.11.107
Link

The structural and electrical properties of samarium doped ceria films formed by e-beam deposition technique

Authors Darius Virbukas, Giedrius Laukaitis
Source
Solid State Ionics
Time of Publication: 2016
Abstract Sm2O3-doped CeO2 (Sm0.15Ce0.85O1.925, SDC) thin films were formed by e-beam evaporation method. Thin films were formed evaporating micro powders (particle size varied from 0.3 to 0.5 μm). The influence of deposition rate on formed thin film structures and surface morphology were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersion spectrometry (EDS), and atomic force microscopy (AFM). The deposition rate of formed SDC thin films was changed from 2 to 16 /s. The electrical properties were investigated as a function of frequency (0.1–106 Hz) at different temperatures (473–873 K). The formed SDC thin ceramic films repeat the crystallographic orientation of the initial powders using different substrates and different deposition rate. It was determined that crystallites size and samarium concentration are decreasing by increasing the deposition rate. The crystallites size decreased from 17.0 nm to 10.4 nm when SDC thin films were deposited on Alloy 600 (Fe-Ni-Cr), and decreased from 13.7 nm to 8.9 nm when were used optical quartz substrate. The best ionic conductivity σtot = 1.66 Sm− 1 at 873 K temperature, activation energy ΔEa = 0.87 eV (σg = 1.66 Sm− 1, σgb = 1.66 Sm− 1) was achieved when 2 /s deposition rate was used. The grain size (in the formed SDC thin films) was ~ 83 nm in this case.
Keywords Electron beam deposition; Samarium doped ceria oxide (SDC); Solid oxide fuel cells (SOFC); Ionic conductivity
Remark http://dx.doi.org/10.1016/j.ssi.2016.12.003
Link

Interstitial oxygen as a source of p-type conductivity in hexagonal manganites

Authors Sandra H. Skjrv, Espen T. Wefring, Silje K. Nesdal, Nikolai H. Gauks, Gerhard H. Olsen, Julia Glaum, Thomas Tybell & Sverre M. Selbach
Source
Nature Communications
Time of Publication: 2016
Abstract Hexagonal manganites, h-RMnO3 (R=Sc, Y, Ho–Lu), have been intensively studied for their multiferroic properties, magnetoelectric coupling, topological defects and electrically conducting domain walls. Although point defects strongly affect the conductivity of transition metal oxides, the defect chemistry of h-RMnO3 has received little attention. We use a combination of experiments and first principles electronic structure calculations to elucidate the effect of interstitial oxygen anions, Oi, on the electrical and structural properties of h-YMnO3. Enthalpy stabilized interstitial oxygen anions are shown to be the main source of p-type electronic conductivity, without reducing the spontaneous ferroelectric polarization. A low energy barrier interstitialcy mechanism is inferred from Density Functional Theory calculations to be the microscopic migration path of Oi. Since the Oi content governs the concentration of charge carrier holes, controlling the thermal and atmospheric history provides a simple and fully reversible way of tuning the electrical properties of h-RMnO3.
Remark doi:10.1038/ncomms13745
Link

Oxygen ion conductivity in samarium and gadolinium stabilized cerium oxide heterostructures

Authors Marius Zienius, Kristina Bockute, Darius Virbukas, Giedrius Laukaitis
Source
Solid State Ionics
Time of Publication: 2016
Abstract Gadolinium (GDC) and samarium (SDC) doped ceria were investigated in terms of multilayer systems, evaporated by e-beam technique on optical quartz, Alloy600 and sapphire substrate. GDC-SDC heterostructures of 1.3 μm thicknesses, composed of 1, 2, 3, 5 and 7 layers and they were investigated by structural and ionic conductivity techniques. Bragg peaks show nanocrystalline state of Gd and Sm doped ceria thin films. XRD patterns show fluorite type structure with space group Fm3m. The XRD analysis of thin films, deposited on quartz substrate, reveals the increase of (220) peak with increasing number of layers. The decrease of (111) peak is slightly notable, also. Thin film heterostructures have a face-centered cubic cell with the following lattice parameters, such as 5.4180 nm for GDC of and of 5.4245 nm for SDC. The scanning electron microscopy cross sectional analysis of three-layered structure clearly indicates the interfaces of different material. There are no visually distinct discontinuities in higher layer structures (5–7 layers). Total conductivity increases linearly with increasing of temperature, but decreases with the increase of number of layers. The highest total ionic conductivity at 1214 K temperature for SDC and GDC thin monolayers was 1.62 S/m and 1.02 S/m, respectively. The activation energy increases with the increase of number of layer as well.
Keywords Multilayer electrolyte; SDC; GDC; e-Beam deposition
Remark http://dx.doi.org/10.1016/j.ssi.2016.11.025
Link

A multistep model for the kinetic analysis of the impedance spectra of a novel mixed ionic and electronic conducting cathode

Authors A. Donazzi, M. Maestri, G. Groppi
Source
Electrochimica Acta
Time of Publication: 2016
Abstract A one-dimensional, heterogeneous and dynamic model is applied to kinetically analyze impedance experiments performed on a novel NdBa0.9Co2O5.6 (NBC) MIEC cathode. The model simulates the spectra in the time domain by accounting for the gas diffusion inside the electrode pores, and for the solid state diffusion of oxygen vacancies inside the bulk of the cathodic material. A detailed kinetic scheme is applied to describe the oxygen reduction mechanism, which includes steps for adsorption and desorption, first and second electronation at the gas/electrode interface, and ion transfer at the electrode/electrolyte interface. The kinetic investigation is based on impedance spectra collected on symmetric NBC/GDC/NBC cells, at open circuit voltage, between 550 and 700C, and 5–100% O2 molar fraction. The vacancies diffusion coefficient and the kinetic parameters of the reaction steps are fitted to describe the data. At the highest temperatures, a sensitivity analysis reveals that the rate determining step is the first electronation of the oxygen adatom, while the second electronation and the interfacial ion transport are kinetically irrelevant. Overall, the model allows to individuate the key parameters for capturing the kinetics of a MIEC cathode.
Keywords EIS; perovskites; kinetics; modeling
Remark http://dx.doi.org/10.1016/j.electacta.2016.11.072
Link

Stability of NASICON materials against water and CO2 uptake

Authors M. Guin, S. Indris, M. Kaus, H. Ehrenberg, F. Tietz, O. Guillon
Source
Solid State Ionics
Time of Publication: 2016
Abstract The stability in ambient conditions of a scandium-based NASICON material, Na3.4Sc2Si0.4P2.6O12, was investigated using impedance spectroscopy, thermogravimetry/differential scanning calorimetry (TG/DSC) and multinuclear magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR). The presence of H2O and CO2 in samples stored in ambient air could be evidenced as well as its impact on the ionic conductivity of the samples. The detected amounts of water and CO2 in the samples had no influence on the measured conductivities at room temperature, which confirmed the absence of protonic conduction in hydrated samples. A loss of conductivity during heating of hydrated samples was due to a loss of contact between the ceramic and the electrode used for the conductivity measurement. The recommendation for handling of NASICON-type materials is therefore: samples require storage in an Ar-filled glove box or in a dry environment to avoid artefacts during high temperature measurements. Nevertheless, the stability of the NASICON-type materials is confirmed since their conductivity is not affected by the moisture.
Keywords Ionic conductivity; NASICON; Sodium; Scandium; ProGasMix
Remark http://dx.doi.org/10.1016/j.ssi.2016.11.006
Link

AgI thin films prepared by laser ablation

Authors Svetlana V. Fokina, Eugene N. Borisov, Vladimir V. Tomaev, Ilya I. Tumkin, Yuri S. Tveryanovich
Source
Solid State Ionics
Volume: 297, Pages: 64–67
Time of Publication: 2016
Abstract High quality and uniform morphology AgI films consisting of crystal grains about 30 nm in size were obtained by the laser (XeCl) ablation method. The designed silver iodide films have crystalline structure, optical and electrical properties corresponding to stoichiometric compound films. We have demonstrated that the laser ablation method commonly used for the preparation of thin films and nanolayered structures with the defined thickness can be successfully used for the deposition of AgI superionic conductor layers as well. The films were studied by XRD, EDA, optical absorption, photoluminescence, and impedance spectroscopies.
Keywords Thin films; Laser ablation; Conductivity; Optical band gap; Luminescence; Morphology; Excitons; XRD; Electron microscopy
Remark http://dx.doi.org/10.1016/j.ssi.2016.10.004
Link

Development of Temperature - Stable Relaxor Dielectrics for High Energy Density Capacitor Applications

Author Connor S. McCue
Source
Time of Publication: 2016
Remark THESIS
Link

Magnetron-Sputtered YSZ and CGO Electrolytes for SOFC

Authors A.A. Solovyev, A.V. Shipilova, I.V. Ionov, A.N. Kovalchuk, S.V. Rabotkin, and V.O. Oskirko
Source
Journal of Electronic Materials
Volume: 45, Issue: 8, Pages: 3921-3928
Time of Publication: 2016
Solid oxide fuel cell, CGO, YSZ, bilayer electrolyte, magnetron sputtering, pulse electron-beam treatment
Remark Link

Thermodynamic properties of the Ba0.75Sr0.25TiO3 nanopowders obtained by hydrothermal synthesis

Authors C.F. Rusti, V. Badilita, A.M. Sofronia, D. Taloi, E.M. Anghel, F. Maxim, C. Hornoiu, C. Munteanu, R.M. Piticescu, S. Tanasescu
Source
Journal of Alloys and Compounds
Volume: 693, Pages: 1000–1010
Time of Publication: 2017
Abstract The paper is devoted to the investigation of the thermodynamic properties of nanostructured Ba0.75Sr0.25TiO3 perovskite material synthesized by hydrothermal method. The thermodynamic parameters obtained by a couple of measurements in both isothermal and dynamic regimes (drop calorimetry, solid-oxide electromotive force measurements, differential scanning calorimetry and thermogravimetry), allow for the investigations of the thermodynamic stability in a large temperature range from room temperature to 1273 K. The influence of the oxygen stoichiometry on the thermodynamic properties was examined using a coulometric titration technique coupled with electromotive force measurements. The results are discussed based on the strong correlation between the thermodynamic parameters and the charge compensation of the material system. X-ray powder diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM) were used for the microstructure and morphology analyses. The variation of the thermal expansion and electrical conductivity associated with the structural changes has been evidenced by thermomechanical measurements and impedance spectroscopy, respectively. Through a combined analysis of all the results, new features related to the understanding of the strong interplay between the thermodynamic properties, microstructure, thermal expansion and electrical conductivity in the hydrothermally prepared Ba0.75Sr0.25TiO3 perovskite material have been revealed.
Keywords Nanostructured materials; Chemical synthesis; Thermodynamic properties; Electromotive force, EMF; Calorimetry; X-ray diffraction
Remark http://dx.doi.org/10.1016/j.jallcom.2016.09.215
Link

Enhanced bulk conductivity of A-site divalent acceptor-doped non-stoichiometric sodium bismuth titanate

Author Solid State Ionics
Source
Fan Yang, Patrick Wu, Derek C. Sinclair
Time of Publication: 2016
Abstract Bismuth-deficient sodium bismuth titanate (nominally Na0.5Bi0.49TiO2.985, NB0.49T) is a good oxide-ion conductor. Here we report the influence of A-site divalent ions, M2 + = Ca2 +, Sr2 + and Ba2 +, on the electrical properties of NB0.49T. A-site divalent doping for Bi3 + enhances the bulk (grain) conductivity by ~ one order of magnitude without changing the conduction mechanism, which is attributed to an increase in the oxygen vacancy concentration based on the doping mechanism Bi3 + + ½ O2 − → M2 +. Among these three dopants, Sr2 + is the most effective in increasing the bulk conductivity due to a combination of its smaller mismatch in ion size with Bi3 +, its intermediate polarisability and lower bond strength to oxygen compared to Ca2 + and Ba2 +. Doping strategies for further improvements to bulk conductivity of NBT materials are discussed based on these results. Comparison with other oxide-ion conductors and initial stability test under reducing atmosphere show the doped non-stoichiometric NBT materials are promising for low and intermediate temperature applications.
Keywords Sodium bismuth titanate; Oxide-ion conductors; Doping; Non-stoichiometry
Remark http://dx.doi.org/10.1016/j.ssi.2016.09.016
Link

Effect of high pressures and temperatures on the structure and properties of CaCu3Ti4O12

Authors N. I. Kadyrova, N. V. Mel’nikova, I. S. Ustinova, Yu. G. Zainulin
Source
Inorganic Materials
Volume: 52, Issue: 10, Pages: 1051–1054
Time of Publication: 2016
Abstract We have prepared ceramic CaCu3Ti4O12 samples by solid-state reaction and investigated the effect of high-pressure/high-temperature processing (p = 8.0 GPa, t = 1100C) on the structure and electrical properties of CaCu3Ti4O12.
Keywords High pressures and temperatures, microstructure, dielectric properties, CaCu3Ti4O12
Remark DOI: 10.1134/S0020168516100083
Link

Evaluation of La0.75Sr0.25Cr0.5Mn0.5O3 protective coating on ferritic stainless steel interconnect for SOFC application

Authors R.K. Lenka, P.K. Patro, Jyothi Sharma, T. Mahata, P.K. Sinha
Source
International Journal of Hydrogen Energy
Time of Publication: 2016
Abstract Ferritic stainless steel (SS) interconnect used for intermediate temperature solid oxide fuel cell has issues associated with the growth of oxide scale on the surface and evaporation of chromium species to the cathode leading to increase in polarization resistance and hence, overall cell resistance. Protective coating is essentially applied over the SS surface to restrict the above phenomena. In the present investigation, strontium doped lanthanum manganese chromite (LSCM) of composition La0.75Sr0.25Cr0.5Mn0.5O3 has been explored as a possible protective coating material on ferritic SS interconnect surface. For this application, fine LSCM powder was synthesized by solution polymerization method. Terpineol based slurry of LSCM was formulated and used for coating on ferritic SS surface by screen printing. LSCM coated ferritic SS was exposed to moist oxygen at 800 C for 300 h and area specific resistance (ASR) of the coating was found to be as low as 2.0 mΩ cm2 after exposure. Microstructure of LSCM coating and the chromium oxide film was investigated using SEM and EDS. The results indicate that LSCM can form an effective protective coating on ferritic stainless steel for SOFC interconnect application.
Keywords Interconnect; Protective coating; LSCM; SOFC
Remark http://dx.doi.org/10.1016/j.ijhydene.2016.08.143
Link

Solid oxide carbonate composite fuel cells: Size effect on percolation

Authors Shalima Shawuti, , Mehmet Ali Glgn
Source
International Journal of Hydrogen Energy
Time of Publication: 2016
Abstract In the studies of solid oxide carbonate composite fuel cell, percolation behaviour of the two phases was investigated as a function of particle size of the oxide phase. The ratio of amount of samarium doped ceria (SDC; Sm0.2Ce0.8O) to Na2CO3 was varied to determine an optimum ionic conductivity as function of oxide particle size. The roles of both phases in the composite electrolyte were investigated. SDC particles were mixed in different amounts of Na2CO3 to obtain composites with carbonate ratios from 1 wt% to 50 wt%. Micro-structural investigations showed that Na2CO3 phase served as the matrix in the micro-structure gluing the oxide particles together. The lowest and the highest carbonate ratios caused low conductivities in the composite as in these samples the 3D connectivity of both phases were disrupted. Low conductivity at both ends of the mixture composition could be interpreted as none of the components of the composite dominated the ionic conductivity. The highest conductivity was obtained at 10 wt% Na2CO3 amount in the composite electrolyte when nano-sized SDC (5–10 nm) oxide powders were used. Two different particle sizes of SDC powders were used to show that the optimum phase ratio, i.e. percolation of both phases, is function of particle size as well. The conductivity in the composite showed percolation behaviour with respect to the two constituent phases.
Keywords Composite electrolyte; SOFC; Interface; Percolation; Carbonate; Impedance
Remark http://dx.doi.org/10.1016/j.ijhydene.2016.07.208, in press
Link

Insights into the enhancement of oxygen mass transport properties of strontium-doped lanthanum manganite interface-dominated thin films

Authors F. Chiabrera, A. Morata, M. Pacios, A. Tarancn
Source
Solid State Ionics
Time of Publication: 2016
Abstract Strontium-doped lanthanum manganite thin films were deposited by pulsed laser deposition on yttria-stabilized zirconia single crystals for a comprehensive electrochemical characterization of the material acting as a cathode. A physically-meaningful electrical model was employed to fit the electrochemical impedance spectroscopy results in order to extract the main oxygen mass transport parameters as a function of the temperature and oxygen partial pressure. The oxygen diffusion and surface exchange coefficients extracted from the analysis showed several orders of magnitude of enhancement with respect to the bulk values reported in the literature and an unexpectedly low dependence with the oxygen partial pressure. Different observations were combined to propose a mechanism for the enhanced incorporation of oxygen in interface-dominated thin films mainly based on the high concentration of oxygen vacancies expected in the grain boundaries.
Remark http://dx.doi.org/10.1016/j.ssi.2016.08.009
Link

Formation of solid solutions in the CdSe–PbSe system under the action of high pressures and temperatures

Authors A. Yu. Chufarov, N. V. Melnikova, N. V. Zarubina, A. N. Ermakov, E. G. Vovkotrub, L. N. Maskaeva, V. F. Markov, Yu. G. Zainulin
Source
Russian Journal of Inorganic Chemistry
Volume: 61, Issue: 8, Pages: 1013–1018
Time of Publication: 2016
Abstract A method was proposed for producing solid solutions in the CdSe–PbSe systems, which is based on heat and high pressure treatment. X-ray powder diffraction analysis showed the formation of substitutional solid solutions CdxPb1–xSe with the NaCl structure, which contained 20, 40, 60, and 80 mol % cadmium selenide. The solid solutions were characterized by scanning electron microscopy, impedance spectroscopy, gas pycnometry, and Raman spectroscopy.
Remark DOI: 10.1134/S0036023616080052
Link

Comparison of characteristics of solid oxide fuel cells with YSZ and CGO film solid electrolytes formed using magnetron sputtering technique

Authors A. A. Solov’ev, A. V. Shipilova, A. N. Koval’chuk, I. V. Ionov, S. V. Rabotkin
Source
Russian Journal of Electrochemistry
Volume: 52, Issue: 7, Pages: 662–668
Time of Publication: 2016
Abstract The work describes the methods of manufacturing single cells of solid oxide fuel cell (SOFC) with thin–film YSZ and CGO electrolytes and also with the bilayer YSZ/CGO electrolyte. Formation of YSZ and CGO films on the supporting NiO–YSZ anode of SOFC was carried out using the combined electron–ionic–plasma deposition technique. The microstructure and phase composition of the formed coatings are studied and also comparative analysis of electrochemical characteristics of single fuel cells with different electrolytes is performed. It is shown that the maximum power density of 1.35 W/cm2 at the temperature of 800C is obtained for the cell with bilayer YSZ/CGO electrolyte. However, the highest performance at lower working temperatures (650–700C) is characteristic for the fuel cell with single–layer CGO electrolyte; its power density is 600–650 mW/cm2.
Keywords Solid oxide fuel cell, CGO, YSZ, bilayer electrolyte, magnetron sputtering, pulsed electron–beam treatment
Remark DOI: 10.1134/S102319351607017X
Link

Nanolayered solid electrolyte (GeSe2)30(Sb2Se3)30(AgI)40/AgI: A new hypothesis for the conductivity mechanism in layered AgI

Authors Yury S. Tveryanovich, Andrei V. Bandura, Svetlana V. Fokina, Evgeny N. Borisov, Robert A. Evarestov
Source
Solid State Ionics
Volume: 294, Pages: 82–89
Time of Publication: 2016
Abstract Using the laser ablation method, films comprised of alternating layers of AgI and (GeSe2)30(Sb2Se3)30(AgI)40 glass were obtained. Individual layer thickness amounts to 10 15 nm, and the total number of layers is about 100. X-ray diffraction (XRD) and film conductivity measurements were carried out during several cycles of heating up to 200 C and cooling to room temperature. It was established that after three cycles of thermal processing specific lateral conductivity of the film is equal to 0.3 S cm− 1 and conductivity activation energy is equal to 0.07 eV at room temperature. Attempts to explain such a high conductivity value based on XRD results did not yield satisfactory results. However, our first-principle calculations within the density functional theory (DFT) showed that in the free layer composed of four AgI planes a rearrangement occurs, resulting in formation of the stable structure of two silver planes on the inside and two iodine planes on the outside (I–Ag–Ag–I). Rearrangement of similar stack of eight or twelve atomic planes results in formation of two or three I–Ag–Ag–I layers loosely bound to each other, accordingly. This suggests that increase in specific conductivity growth of multilayer film as a consequence of cyclic heating and cooling may be connected with AgI stratification on its boundary with chalcogenide glass and following stabilization of layered phases mentioned above. The existence of an empty space between the layers that is constrained by iodine ion planes should facilitate silver ion diffusion along the layers.
Keywords Glass-composite; Laser-ablation method; Ionic conductivity; AgI polymorphs; DFT calculations
Remark doi:10.1016/j.ssi.2016.07.004
Link

Tin–Zinc oxide composite ceramics for selective CO sensing

Authors Paul Chesler, Cristian Hornoiu, Susana Mihaiu, Cornel Munteanu, Mariuca Gartner
Source
Ceramics International
Time of Publication: 2016
Abstract Composite metal oxide gas sensors were intensely studied over the past years having superior performance over their individual oxide components in detecting hazardous gases. A series of pellets with variable amounts of SnO2 (0–50 mol%) was prepared using wet homogenization of the component oxides leading to the composite tin-zinc ceramic system formation. The annealing temperature was set to 1100 C. The samples containing 2.5 mol% SnO2 and 50 mol% SnO2 were annealed also at 1300 C, in order to observe/to investigate the influence of the sintering behaviour on CO detection. The sensor materials were morphologically characterized by scanning electron microscopy (SEM). The increase in the SnO2 amount in the composite ceramic system leads to higher sample porosity and an improved sensitivity to CO. It was found that SnO2 (50 mol%) - ZnO (50 mol%) sample exhibits excellent sensing response, at a working temperature of 500 C, for 5 ppm of CO, with a fast response time of approximately 60 s and an average recovery time of 15 min. Sensor selectivity was tested using cross-response to CO, methane and propane. The results indicated that the SnO2 (50 mol%)-ZnO (50 mol%) ceramic compound may be used for selective CO sensing applications.
Keywords SnO2–ZnO; Composites; Sensors; Selective detection of CO
Remark doi:10.1016/j.ceramint.2016.07.102
Link

Synthesis and electrical properties of new perovskite-like AMn3V4O12 (A = Ca, Ce, and Sm) compounds

Authors N. I. Kadyrova, Yu. G. Zaynulin, A. P. Tyutyunnik, N. V. Melnikova, A. A. Mirzorakhimov
Source
Bulletin of the Russian Academy of Sciences: Physics
Volume: 80, Issue: 6, Pages: 620–623
Time of Publication: 2016
Abstract AMn3V4O12 (A = Ca, Ce, and Sm) compounds with a perovskite structure are synthesized at high pressures and temperatures. The crystalline structure of these compounds (space group Im3Z = 2) is determined via X-ray analysis. If ions in the A sublattice are changed in the order Ca2+–Sm3+–Ce3+, the valence is redistributed from Ca2+Mn32+V44+O12 to Sm3+Mn32+V43.75+O12, and to Ce3+Mn32+V43.75+O12. The temperature dependences of the electrical resistivity are studied.
Remark Link

Tailoring transport properties through nonstoichiometry in BaTiO3–BiScO3 and SrTiO3–Bi(Zn1/2Ti1/2)O3 for capacitor applications

Authors Nitish Kumar, David P. Cann
Source
Journal of Materials Science
Volume: 51, Issue: 20, Pages: 9404–9414
Time of Publication: 2016
Abstract The ceramic perovskite solid solutions BaTiO3–BiScO3 (BT–BS) and SrTiO3–Bi(Zn1/2Ti1/2)O3 (ST–BZT) are promising candidates for high-temperature and high-energy density dielectric applications. A-site cation nonstoichiometry was introduced in these two ceramic systems to investigate their effects on the dielectric and transport properties using temperature- and oxygen partial pressure-dependent AC impedance spectroscopy. For p-type BT–BS ceramics, the addition of excess Bi led to effective donor doping along with a significant improvement in insulation properties. A similar effect was observed on introducing Ba vacancies onto the A-sublattice. However, Bi deficiency registered an opposite effect with effective acceptor doping and a deterioration in the bulk resistivity values. For n-type intrinsic ST–BZT ceramics, the addition of excess Sr onto the A-sublattice resulted in a decrease in resistivity values, as expected. Introduction of Sr vacancies or addition of excess Bi on A-site did not appear to affect the insulation properties in air. These results indicate that minor levels of nonstoichiometry can have an important impact on the material properties, and furthermore it demonstrates the difficulties encountered in trying to establish a general model for the defect chemistry of Bi-containing perovskite systems.
Remark DOI: 10.1007/s10853-016-0186-z
Link

Leaching effect in gadolinia-doped ceria aqueous suspensions for ceramic processes

Authors A. Caldarelli, E. Mercadelli, S. Presto, M. Viviani, A. Sanson
Source
Journal of Power Sources
Volume: 326, Issue: 15, Pages: 70–77
Time of Publication: 2016
Abstract Gadolinium doped ceria (CGO) is a commonly used electrolytic material for Solid Oxide Fuel Cells (SOFCs) and for this reason different shaping methods for its deposition are reported in literature. Most of these processes are based on the use of organic-based CGO suspensions, but water-based processes are acquiring increasingly interest for their economical and environmental friendly properties. In this paper we reported how the components of water-based suspension and some unexpected process parameters can deeply affect the functional properties of the final powder. In particular, we observed that CGO powders are strongly affected by ionic leaching induced by furoic acid used as dispersant: the extent of this leaching was related to the dispersant concentration and suspension’s ball-milling-time; the phenomenon was confirmed by ICP-AES analyses on suspensions surnatant. Most importantly, ionic leaching affected the electrical properties of CGO: leached powder showed a higher ionic conductivity as a consequence of a partial removal of Gd ions at the grain boundaries. This work is therefore pointing out that when considering water-based suspensions, it is extremely important to carefully consider all the process parameters, including the organic components of the ceramic suspension, as these could lead to unexpected effects on the properties of the powder, affecting the performance of the final shaped material.
Keywords Gadolinium doped ceria; Water-based suspensions; Furoic acid; Ionic leaching; Electrical conductivity
Remark doi:10.1016/j.jpowsour.2016.06.069
Link

Structural, textural, surface chemistry and sensing properties of mesoporous Pr, Zn modified SnO2–TiO2 powder composites

Authors I. Dascalu, D. Culita, J.M. Calderon-Moreno, P. Osiceanu, C. Hornoiu, M. Anastasescu, S. Somacescu, M. Gartner
Source
Ceramics International
Volume: 43, Issue: 13, Pages: 14992–14998
Time of Publication: 2016
Abstract Mesoporous Zn and Pr modified SnO2-TiO2 mixed powders (Sn:Ti:Zn:Pr contents 60:20:15:5) have been prepared by a modified sol–gel method involving Tripropylamine (TPA) as chelating agent, TritonX100 as template and Polyvinylpyrrolidone as dispersant and stabilizer, respectively. The obtained gels have been dried at different temperatures and calcined in air at 600 and 800 C, respectively. Phase identification of the synthesized samples and their evolution with the calcination temperature has been performed by X-ray diffraction. N2 adsorption/desorption isotherms were found to be characteristic for mesoporous materials, showing relatively low values for the specific surface area (15–32 m2 g−1) and nanometric sized pores. In case of the sample calcined at 800 C, a bimodal pore size distribution can be observed, with maxima at 20 and 60 nm. SEM results demonstrate a porous nanocrystalline morphology stable up to 800 C. The surface chemistry investigated by XPS reveals the presence of the elements on the surface as well as the oxidation states for the detected elements. At 800 C a diffusion process of Sn from surface to the subsurface/bulk region accompanied by a segregation of Ti and Zn to the surface is noticed, while Pr content is unchanged. The sensing properties of the prepared powders for CO detection have been tested in the range of 250–2000 ppm and working temperatures of 227–477 C.
Keywords SnO2; TiO2; Sol–gel; Mesoporous materials; CO detection
Remark doi:10.1016/j.ceramint.2016.06.146
Link

New promising NASICON material as solid electrolyte for sodium-ion batteries: Correlation between composition, crystal structure and ionic conductivity of Na3 + xSc2SixP3 − xO12

Authors M. Guin, F. Tietz, O. Guillon
Source
Solid State Ionics
Volume: 293, Pages: 18–26
Time of Publication: 2016
Abstract In the search for novel sodium-ion conductors to be used in batteries for grid application, the thoroughly studied class of NASICON materials is of great interest due to compositional diversity and high ionic conductivity. The solid solution Na3 + xSc2(SiO4)x(PO4)3 − x with 0.05 ≤ x ≤ 0.8 was investigated for the first time. The various compositions were synthesized by solid state reaction and their crystallographic and electrical properties were measured. As a result, one of the best sodium-conductive NASICON materials to date was obtained for x = 0.4 (σNa,Total = 6.9 10− 4 S cm− 1 at 25 C). Furthermore, the importance of the sodium concentration and size of lattice parameters on the ionic conductivity were investigated. The bulk ionic conductivity was correlated with the structural parameters along the conduction pathway of the sodium ions and confirm the key influence of the interatomic Na–O distances on sodium ion transport.
Keywords Ionic conductivity; NASICON; Sodium; Scandium; Solid electrolyte; Battery
Remark doi:10.1016/j.ssi.2016.06.005
Link

Effect of Nb Doping on Hydration and Conductivity of La27W5O55.5−δ

Authors Cao, Y., Duan, N., Jian, L., Evans, A. and Haugsrud, R.
Source
J. Am. Ceram. Soc.
Time of Publication: 2016
Abstract Hydration properties and electrical characteristics of the high-temperature proton conductor La27(W0.85Nb0.15)5O55.5−δ are investigated by means of thermogravimetry, impedance spectroscopy, and the electromotive force (EMF) method as a function of temperature, water vapor, and oxygen partial pressures, as well as isotope exchange measurements in order to elucidate the mechanism and thermodynamics of protons formation and transport. The highest proton conductivity, 1.3 10-3 S/cm, is achieved at 700C in wet O2. Proton self-diffusion coefficients are estimated from thermogravimetric measurements of hydration and conductivity data. Comparison of the conductivity characteristics between nominally pure and Nb-substituted materials reveals that the ionic conductivity increases and the activation energy decreases with Nb doping. These differences are discussed to reflect changes in the structure promoting ionic transport rather than changing the concentration of defects to any large extent.
Keywords Lanthanum tungstate; proton concentration; proton conductivity; H/D isotope effect
Remark doi:10.1111/jace.14346
Link

Synthesis, characterization and performance of robust poison-resistant ultrathin film yttria stabilized zirconia – nickel anodes for application in solid electrolyte fuel cells

Authors F.J. Garcia-Garcia, F. Yubero, J.P. Espins, A.R. Gonzlez-Elipe, R.M. Lambert
Source
Journal of Power Sources
Volume: 324, Pages: 679–686
Time of Publication: 2016
Abstract We report on the synthesis of undoped ∼5 μm YSZ-Ni porous thin films prepared by reactive pulsed DC magnetron sputtering at an oblique angle of incidence. Pre-calcination of the amorphous unmodified precursor layers followed by reduction produces a film consisting of uniformly distributed tilted columnar aggregates having extensive three-phase boundaries and favorable gas diffusion characteristics. Similarly prepared films doped with 1.2 at.% Au are also porous and contain highly dispersed gold present as Ni-Au alloy particles whose surfaces are strongly enriched with Au. With hydrogen as fuel, the performance of the undoped thin film anodes is comparable to that of 10–20 times thicker typical commercial anodes. With a 1:1 steam/carbon feed, the un-doped anode cell current rapidly falls to zero after 60 h. In striking contrast, the initial performance of the Au-doped anode is much higher and remains unaffected after 170 h. Under deliberately harsh conditions the performance of the Au-doped anodes decreases progressively, almost certainly due to carbon deposition. Even so, the cell maintains some activity after 3 days operation in dramatic contrast with the un-doped anode, which stops working after only three hours of use. The implications and possible practical application of these findings are discussed.
Keywords Magnetron sputtering; Oblique angle deposition; Thin film anodes; Carbon-tolerant; SOFC
Remark doi:10.1016/j.jpowsour.2016.05.124
Link

Electrical characterization of amorphous LiAlO2 thin films deposited by atomic layer deposition

Authors Yang Hu, Amund Ruud, Ville Miikkulainen, Truls Norby, Ola Nilsen and Helmer Fjellvg
Source
RSC Advances
Volume: 6, Issue: 65, Pages: 60479-60486
Time of Publication: 2016
Abstract LiAlO2 thin films deposited by atomic layer deposition (ALD) have a potential application as an electrolyte in three-dimensional (3D) all-solid-state microbatteries. In this study, Li-ion conductivity of such films is investigated by both in-plane and cross-plane methods. LiAlO2 thin films with a Li composition of [Li]/([Li] + [Al]) = 0.46 and an amorphous structure were grown by ALD with thicknesses of 90, 160 and 235 nm on different substrates. The electrical characterization was conducted by impedance spectroscopy using inert electrodes over a temperature range of 25–200 C in an inert atmosphere. In-plane conductivities were obtained from films on insulating sapphire substrates, whereas cross-plane conductivities were measured from films on conducting titanium substrates. For the first time, comparison of the in-plane and cross-plane conductivities in these ALD LiAlO2 films has been achieved. More comparable results are obtained using a cross-plane method, whereas in-plane conductivity measurements demonstrate a considerable thickness-dependence with thinner film thickness. The room-temperature conductivity of the LiAlO2 films has been determined to be in the order of 10−10 S cm−1 with an activation energy of ca. 0.8 eV.
Remark DOI: 10.1039/C6RA03137D
Link

Thin film YSZ-based limiting current-type oxygen and humidity sensor on thermally oxidized silicon substrates

Author Shunsuke Akasaka
Source
Sensors and Actuators B: Chemical
Volume: 236, Pages: 499–505
Time of Publication: 2016
Abstract In this paper, we propose a thin film yttria-stabilized-zirconia (YSZ)-based limiting current-type oxygen and humidity sensor. These sensors were fabricated from layers of thin films on thermally oxidized silicon substrates, with the intention of installing such sensors onto microheaters. Sputtered porous Pt cathode are situated beneath the YSZ films, and are designed to provide a gas diffusion layer as well as function as electrodes. The porous Pt layer exhibits good performance as a gas diffusion layer because of its small pore size. Optimized YSZ sputtering growth conditions result in in-plane densification without the presence of cracks. The temperature dependence of the oxygen sensor’s level of limiting current was T −0.5. This result was attributed to the shrinkage of the extremely small pores in the gas diffusion layer. Between 450 and 550 C, following the application of a voltage of 1.1 V, the time response measurements show a rapid response of a few seconds. The oxygen concentration and water vapor pressure correspond to the level of the limiting current at 1.1 V and 1.8 V, respectively.
Keywords Yttria-stabilized-zirconia; Limiting current; Oxygen sensor; Humidity sensor; Thin film; Silicon substrate
Remark doi:10.1016/j.snb.2016.06.025
Link

Conduction Mechanisms in BaTiO3–Bi(Zn1/2Ti1/2)O3 Ceramics

Authors Kumar, N., Patterson, E. A., Frmling, T. and Cann, D. P.
Source
J. Am. Ceram. Soc.
Time of Publication: 2016
Abstract Polycrystalline BaTiO3–Bi(Zn1/2Ti1/2)O3 (BT–BZT) ceramics have superior dielectric properties for high-temperature and high-energy density applications as compared to the existing materials. While it has been shown that the addition of BZT to BT leads to an improvement in resistivity by two orders of magnitude, in this study impedance spectroscopy is used to demonstrate a novel change in conduction mechanism. While nominally undoped BT exhibits extrinsic-like p-type conduction, it is reported that BT–BZT ceramics exhibit intrinsic n-type conduction using atmosphere-dependent conductivity measurements. Annealing studies and Seebeck measurements were performed and confirmed this result. For BT, resistivity values were higher for samples annealed in nitrogen as compared to oxygen, whereas the opposite responses were observed for BZT-containing solid solutions. This suggests a fundamental change in the defect equilibrium conditions upon the addition of BZT to the solid solution that lowered the carrier concentration and changed the sign of the majority charge carrier. This is then also linked to the observed improvement in resistivity in BT–BZT ceramics as compared to undoped BT.
Remark doi:10.1111/jace.14313
Link

Effect of Nd-deficiency on electrochemical properties of NdBaCo2O6−δ cathode for intermediate-temperature solid oxide fuel cells

Authors Kaihua Yia,Liping Sun, Qiang Li, Tian Xia, Lihua Huo, Hui Zhao, Jingwei Li, Zhe L, Jean-Marc Bassat, Aline Rougier, Sbastien Fourcade, Jean-Claude Grenier
Source
International Journal of Hydrogen Energy
Volume: 41, Issue: 24, Pages: 10228–10238
Time of Publication: 2016
Abstract Nd1−xBaCo2O6−δ (N1−xBCO) is evaluated as cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The effects of Nd-deficiency on the crystal structure, thermal expansion behavior, electrical conductivity and electrochemical performance are studied. N1−xBCO oxides crystallize in the orthorhombic symmetry with Pmmm space group. A good chemical compatibility between N1−xBCO and CGO electrolyte is found at 1100 C in air. Introducing Nd-deficiency promotes the formation of oxygen vacancy, and significantly improves the electrochemical performance of N1−xBCO cathodes. The lowest area specific resistance (ASR) value of 0.043 Ω cm2 is obtained on the N0.96BCO cathode at 700 C in air. The rate limiting step for electrochemical oxygen reduction reaction (ORR) is charge transfer process at the interface. The power output of the electrolyte supported cell Ni-CGO/CGO/N0.96BCO reaches 0.6 W cm−2 at 700 C.
Keywords Solid oxide fuel cell; Double perovskite; Nd-deficiency; Cathode; Electrode reaction
Remark doi:10.1016/j.ijhydene.2016.04.248
Link

Controlling mixed conductivity in Na1/2Bi1/2TiO3 using A-site non-stoichiometry and Nb-donor doping

Authors Linhao Li, Ming Li, Huairuo Zhang, Ian M. Reaney and Derek C. Sinclair
Source
J. Mater. Chem. C
Volume: 4, Pages: 5779-5786
Time of Publication: 2016
Abstract Precise control of electronic and/or ionic conductivity in electroceramics is crucial to achieve the desired functional properties as well as to improve manufacturing practices. We recently reported the conventional piezoelectric material Na1/2Bi1/2TiO3 (NBT) can be tuned into a novel oxide-ion conductor with an oxide-ion transport number (tion) > 0.9 by creating bismuth and oxygen vacancies. A small Bi-excess in the nominal starting composition (Na0.50Bi0.50+xTiO3+3x/2, x = 0.01) or Nb-donor doping (Na0.50Bi0.50Ti1−yNbyO3+y/2, 0.005 ≤ y ≤ 0.030) can reduce significantly the electrical conductivity to create dielectric behaviour by filling oxygen vacancies and suppressing oxide ion conduction (tion ≤ 0.10). Here we show a further increase in the starting Bi-excess content (0.02 ≤ x ≤ 0.10) reintroduces significant levels of oxide-ion conductivity and increases tion ∼ 0.4–0.6 to create mixed ionic/electronic behaviour. The switch from insulating to mixed conducting behaviour for x > 0.01 is linked to the presence of Bi-rich secondary phases and we discuss possible explanations for this effect. Mixed conducting behaviour with tion ∼ 0.5–0.6 can also be achieved with lower levels of Nb-doping (y ∼ 0.003) due to incomplete filling of oxygen vacancies without the presence of secondary phases. NBT can now be compositionally tailored to exhibit three types of electrical behaviour; Type I (oxide-ion conductor); Type II (mixed ionic-electronic conductor); Type III (insulator) and these results reveal an approach to fine-tune tion in NBT from near unity to zero. In addition to developing new oxide-ion and now mixed ionic/electronic NBT-based conductors, this flexibility in control of oxygen vacancies allows fine-tuning of both the dielectric/piezoelectric properties and design manufacturing practices for NBT-based multilayer piezoelectric devices.
Remark DOI: 10.1039/C6TC01719C
Link

Influence of cathode functional layer composition on electrochemical performance of solid oxide fuel cells

Authors Antnio de Pdua Lima Fernandes, Eric Marsalha Garcia, Rubens Moreira de Almeida, Hosane Aparecida Taroco, Edyth Priscilla Campos Silva, Rosana Zacarias Domingues, Tulio Matencio
Source
Journal of Solid State Electrochemistry
Time of Publication: 2016
Abstract In this work, anode-supported solid oxide fuel cells (SOFC) were tested with a yttria-stabilized zirconia (YSZ) (8 mol% Y2O3-ZrO2)/gadolinium-doped ceria (GDC) (Ce0.9Gd 0.1O1.95) bilayer electrolyte and two lanthanum strontium cobalt ferrite (LSCF) composition as functional cathode layer: La0.6Sr0.4Co0.8Fe0.2O3-δ (LSCF 1) and La0.60Sr0.40Co0.2Fe0.8O3-δ (LSCF 2). The functional cathode layers were made of 50 % (w/w) LSCF and 50 % (w/w) GDC. Microstructural characterization was performed by scanning electron microscopy and X-ray diffraction. Electrochemical impedance spectroscopy (EIS) and power measurements were performed under oxygen and hydrogen atmospheres. The microscopy studies showed that the LSCF 2 functional layer is more uniform and adherent to the electrolyte and the cathode collector than the LSCF 1 functional layer, which has cracks, chips, and lower adhesion. The use of the LSCF 2 layer allowed an approximately 25-fold reduction in ohmic resistance (0.06 Ω cm−2) compared with the LSCF 1 layer (1.5 Ω cm−2). The power measurements showed a considerable increase in the power cell using LSCF 2 (approximately 420 mW cm−2) compared with the power cell using LSCF 1 (approximately 180 mW cm−2).
Keywords SOFC, LSCF, Interface, Electrochemical performance, Cathode, Functional layer
Remark First Online: 20 May 2016. DOI: 10.1007/s10008-016-3241-4
Link

Mechanical degradation under hydrogen of yttrium doped barium zirconate electrolyte material prepared with NiO additive

Authors D. Ciria, M. Ben Hassine, M. Jimnez-Melendo, A. Iakovleva, P. Haghi-Ashtiani, V. Aubin, G. Dezanneau
Source
Journal of Power Sources
Volume: 321, Pages: 226–232
Time of Publication: 2016
Abstract Recently, a novel process was presented to fabricate dense yttrium-doped barium zirconate electrolytes with high proton conductivity. This process was based on the use of a NiO additive during reactive sintering. We show here that materials made from this process present a fast degradation of mechanical properties when put in hydrogen-rich conditions, while material made from conventional sintering without NiO aid remains intact in the same conditions. The fast degradation of samples made from reactive sintering, leading to sample failure under highly compressive conditions, is due to the reduction of NiO nanoparticles at grain boundaries as shown from structural and chemical analyses using Transmission Electron Microscopy. By the present study, we alert about the potential risk of cell failure due to this mechanical degradation.
Keywords PCFCs; Mechanical properties; BZY; Solid state reactive sintering
Remark doi:10.1016/j.jpowsour.2016.05.001
Link

Electrochemical Property Assessment of Pr2CuO4 Submicrofiber Cathode for Intermediate-Temperature Solid Oxide Fuel Cells

Authors Ting Zhao, Li-Ping Sun, Qiang Li, Li-Hua Huo, Hui Zhao, Jean-Marc Bassat, Aline Rougier, Sbastien Fourcade and Jean-Claude Grenier
Source
Journal of Electrochemical Energy Conversion and Storage
Volume: 13, Issue: 1, Pages: 011006
Time of Publication: 2016
Abstract The Pr2CuO4 (PCO) submicrofiber precursors are prepared by electrospinning technique and the thermo-decomposition procedures are characterized by thermal gravity (TG), X-ray diffraction (XRD), Fourier transform infrared spectoscopy (FT-IR), and scanning electron microscopy (SEM), respectively. The fibrous PCO material was formed by sintering the precursors at 900 C for 5 hrs. The highly porous PCO submicrofiber cathode forms good contact with the Ce0.9Gd0.1O1.95 (CGO) electrolyte after heat-treated at 900 C for 2 hrs. The performance of PCO submicrofiber cathode is comparably studied with the powder counterpart at various temperatures. The porous microstructure of the submicrofiber cathode effectively increases the three-phase boundary (TPB), which promotes the surface oxygen diffusion and/or adsorption process on the cathode. The PCO submicrofiber cathode exhibits an area specific resistance (ASR) of 0.38 Ω cm2 at 700 C in air, which is 30% less than the PCO powder cathode. The charge transfer process is the rate limiting step of the oxygen reduction reaction (ORR) on the submicrofiber cathode. The maximum power densities of the electrolyte-support single cell PCO|CGO|NiO-CGO reach 149 and 74.5 mW cm−2 at 800 and 700 C, respectively. The preliminary results indicate that the PCO submicrofiber can be considered as potential cathode for intermediate temperature solid fuel cells (IT-SOFCs).
Remark doi: 10.1115/1.4033526
Link

Direct conversion of methane to aromatics in a catalytic co-ionic membrane reactor

Authors S.H.Morejudo, R.Zanon, S.escolastico, I. Yuste-Tirados, H. Malerd-Fjeld, P.K. Vestre, W.G.Coors, A.Martinez, T.Norby, J.M.Serra, C.Kjlseth
Source
Science
Volume: 353, Issue: 6299, Pages: 563-566
Publisher: American Association for the Advancement of Science (AAAS), ISBN: Print ISSN:0036-8075 Online ISSN:1095-9203, Time of Publication: 2016-08
Abstract Nonoxidative methane dehydroaromatization (MDA: 6CH4 ↔ C6H6 + 9H2) using shape-selective Mo/zeolite catalysts is a key technology for exploitation of stranded natural gas reserves by direct conversion into transportable liquids. However, this reaction faces two major issues: The one-pass conversion is limited by thermodynamics, and the catalyst deactivates quickly through kinetically favored formation of coke. We show that integration of an electrochemical BaZrO3-based membrane exhibiting both proton and oxide ion conductivity into an MDA reactor gives rise to high aromatic yields and improved catalyst stability. These effects originate from the simultaneous extraction of hydrogen and distributed injection of oxide ions along the reactor length. Further, we demonstrate that the electrochemical co-ionic membrane reactor enables high carbon efficiencies (up to 80%) that improve the technoeconomic process viability. Methane gas is expensive to ship. It is usually converted into carbon monoxide and hydrogen and then liquefied. This is economically feasible only on very large scales. Hence, methane produced in small amounts at remote locations is either burned or not extracted. A promising alternative is conversion to benzene and hydrogen with molybdenumzeolite catalysts. Unfortunately, these catalysts deactivate because of carbon buildup; plus, hydrogen has to be removed to drive the reaction forward. Morejudo et al. address both of these problems with a solid-state BaZrO3 membrane reactor that electrochemically removes hydrogen and supplies oxygen to suppress carbon buildup.
Keywords CMR, MDA, catalytic membrane reactor, ZSM-5, MCM-22, FBR, FBR-PolyM, Pd-CMR, Co-ionic CMR, FT, ProboStat CMR base unit (NorECs)
Remark http://science.sciencemag.org/highwire/filestream/682540/field_highwire_adjunct_files/0/Morejudo.SM.pdf
BaZrO3
BaZrO3
Link

Magnetron-Sputtered YSZ and CGO Electrolytes for SOFC

Authors A. A. Solovyev , A. V. Shipilova, I. V. Ionov, A. N. Kovalchuk, S. V. Rabotkin, V. O. Oskirko
Source
Journal of Electronic Materials
Time of Publication: 2016
Abstract Reactive magnetron sputtering has been used for deposition of yttria-stabilized ZrO2 (YSZ) and gadolinium-doped CeO2 (CGO) layers on NiO-YSZ commercial anodes for solid oxide fuel cells. To increase the deposition rate and improve the quality of the sputtered thin oxide films, asymmetric bipolar pulse magnetron sputtering was applied. Three types of anode-supported cells, with single-layer YSZ or CGO and YSZ/CGO bilayer electrolyte, were prepared and investigated. Optimal thickness of oxide layers was determined experimentally. Based on the electrochemical characteristics of the cells, it is shown that, at lower operating temperatures of 650C to 700C, the cells with single-layer CGO electrolyte are most effective. The power density of these fuel cells exceeds that of the cell based on YSZ single-layer electrolyte at the same temperature. Power densities of 650 mW cm−2 and 500 mW cm−2 at 700C were demonstrated by cells with single-layer YSZ and CGO electrolyte, respectively. Significantly enhanced maximum power density was achieved in a bilayer-electrolyte single cell, as compared with cells with a single electrolyte layer. Maximum power density of 1.25 W cm−2 at 800C and 1 W cm−2 at 750C under voltage of 0.7 V were achieved for the YSZ/CGO bilayer electrolyte cell with YSZ and CGO thickness of about 4 μm and 1.5 μm, respectively. This signifies that the YSZ thin film serves as a blocking layer to prevent electrical current leakage in the CGO layer, leading to the overall enhanced performance. This performance is comparable to the state of the art for cells based on YSZ/CGO bilayer electrolyte.
Keywords Solid oxide fuel cell CGO YSZ bilayer electrolyte magnetron sputtering pulse electron-beam treatment
Remark Link

Characteristics of Cu and Mo-doped Ca3Co4O9−δ cathode materials for use in solid oxide fuel cells

Authors Sea-Fue Wang, Yung-Fu Hsu, Jing-Han Chang, Soofin Cheng, Hsi-Chuan Lu
Source
Ceramics International
Time of Publication: 2016
Abstract In this study, Cu and Mo ions were doped in Ca3Co4O9−δ to improve the electrical conductivity and electrochemical behavior of Ca3Co4O9−δ ceramic and the performance of a solid oxide fuel cell (SOFC) single cell based on NiO-SDC/SDC/doped Ca3Co4O9−δ-SDC were examined. Cu substitution in the monoclinic Ca3Co4O9−δ ceramic effectively enhanced the densification, slightly increased the grain size, and triggered the formation of some Ca3Co2O6; however, no second phase was found in porous Mo-doped Ca3Co4O9−δ ceramics even when the sintering temperature reached 1050 C. Substitution of Cu ions caused slight increase in the Co3+ and Co4+ contents and decrease in the Co2+ content; however, doping with Mo ions showed the opposite trend. Doping the Ca3Co4O9−δ ceramic with a small amount of Cu or Mo increased its electrical conductivity. The maximum electrical conductivity measured was 218.8 S cm−1 for the Ca3Co3.9Cu0.1O9−δ ceramic at 800 C. The Ca3Co3.9Cu0.1O9−δ ceramic with a coefficient of thermal expansion coefficient of 12.110−6 K−1 was chosen as the cathode to build SOFC single cells consisting of a 20 μm SDC electrolyte layer. Without optimizing the microstructure of the cathode or hermetically sealing the cell against the gas, a power density of 0.367 Wcm−2 at 750 C was achieved, demonstrating that Cu-doped Ca3Co4O9−δ can be used as a potential cathode material for IT-SOFCs.
Keywords Solid oxide fuel cell; Cathode; Impedance; Cell performance
Remark In Press, doi:10.1016/j.ceramint.2016.04.037
Link

Synthesis and characterization of robust, mesoporous electrodes for solid oxide fuel cells

Authors Laura Almar, Alex Morata, Marc Torrell, Mingyang Gong, Meilin Liu, Teresa Andreu and Albert Tarancn
Source
Journal of Materials Chemistry A
Time of Publication: 2016
Abstract The use of mesoporous electrodes in solid oxide cells would lead to a significant enhancement of the performance due to their high surface area and large number of active sites for electrochemical reactions. However, their application in real devices is still hindered by the potential instability of the mesostructure and morphology at high temperatures required for device fabrication and under severe conditions for high-current, long-term operation. Here we report our findings on the preparation and characterization of mesoporous electrodes based on ceria infiltrated with catalysts: an anode consisting of a Ce0.8Sm0.2O1.9 (SDC) scaffold infiltrated with Ni and a cathode consisting of an SDC scaffold infiltrated with Sm0.5Sr0.5CoO3−δ (SSC). In particular, a doped-zirconia electrolyte supported cell with a mesoporous Ni–SDC anode and a mesoporous SSC–SDC cathode demonstrates an excellent peak power density of 565 mW cm−2 at 750 C (using humidified hydrogen as the fuel). More importantly, both mesoporous electrodes display remarkable stability, yielding a combined electrode virtual non-degradation for the last 500 hours of the test at a constant current density of 635 mA cm−2 at 750 C, demonstrating the potential of these mesoporous materials as robust electrodes for solid oxide fuel cells or other high-temperature electrochemical energy storage and conversion devices.
Remark DOI: 10.1039/C6TA00321D
Link

Fluorite-like compounds with high anionic conductivity in Nd2MoO6 – Bi2O3 system

Authors E.P. Kharitonova, V.I. Voronkova, D.A. Belov, E.I. Orlova
Source
International Journal of Hydrogen Energy
Time of Publication: 2016
Abstract A wide range of (Bi2O3)x(Nd2O3)(1−x)/2(MoO3)(1−x)/2 solid solutions with the structure of the anion-conducting bismuth oxide was found in the Bi2O3–Nd2MoO6 join of ternary Bi2O3–MoO3–Nd2O3 system at 0.5 ≤ x ≤ 1. In said concentration range the compounds with large (0.92 ≤ x ≤ 0.98) and small (0.5 ≤ x < 0.6) bismuth content are tetragonal at room temperature. In the intermediate concentration range (0.67 ≤ x ≤ 0.9) cubic δ-Bi2O3 structure is stabilized at room temperature. It is shown that two tetragonal phases observed at different bismuth concentrations differ from each other in their polymorphism and behavior of the unit cell parameters. All the obtained compounds show high conductivity that reaches 0.1 S/cm (for a cubic sample with x = 0.8 at 800 C).
Keywords Bi2O3; Nd2O3; MoO3; Polymorphism; Oxygen conductivity
Remark In press, doi:10.1016/j.ijhydene.2016.03.046
Link

Structural study and proton conductivity in BaCe0.7Zr0.25−xYxZn0.05O3 (x = 0.05, 0.1, 0.15, 0.2 & 0.25)

Authors Ahmed Afif, Nikdalila Radenahmad, Chee Ming Lim, Mohamad Iskandar Petra, Md. Aminul Islam, Seikh Mohammad Habibur Rahman, Sten Eriksson, Abul Kalam Azad
Source
International Journal of Hydrogen Energy
Time of Publication: 2016
Abstract Solid oxide fuel cell (SOFC) has been considered to generate power represented by conductivity. Zinc doped Barium Cerium Zirconium Yttrium oxide (BCZYZn) has been found to offer high protonic conductivity and high stability as being electrolyte for proton-conducting SOFCs. In this study, we report a new series of proton conducting materials, BaCe0.7Zr0.25−xYxZn0.05O3 (x = 0.05, 0.1, 0.15, 0.2 and 0.25). The materials were synthesized by solid state reaction route and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermal expansion, particle size and impedance spectroscopy (IS). Rietveld analysis of the XRD data reveal a cubic perovskite structure with Pm-3m space group up to composition x = 0.15. For x = 0.15 and 0.20, the materials have structural phase change to orthorhombic in the Pbnm space group. Scanning electron microscopy images show high density materials. Thermal expansion measurements show that the thermal expansion coefficient is in the range 10.0–11.0 10−6/C. Impedance spectroscopy shows higher ionic conduction under wet condition compared to dry condition. Y content of 25% (BCZYZn25) exhibits highest conductivity of 1.84 10−2 S/cm in wet Argon. This study indicated that perovskite electrolyte BCZYZn is promising material for the next generation of intermediate temperature solid oxide fuel cells (IT-SOFCs).
Keywords Proton conductor; Sinterability; Rietveld refinement; Conductivity; SOFC electrolyte
Remark In Press, doi:10.1016/j.ijhydene.2016.02.135
Link

Ca-doped fluorite-like compounds based on Nd5Mo3O16

Authors V.I. Voronkova, E.P. Kharitonova, E.I. Orlova, A.V. Levchenko, A.M. Antipin, N.I. Sorokina, D.A. Belov
Source
Journal of Alloys and Compounds
Time of Publication: 2016
Abstract We have studied phase relations in a molybdenum oxide-rich region of the ternary system CaO–Nd2O3–MoO3. Using polycrystalline samples prepared by solid-state reactions in air, the system has been shown to contain a rather broad region of cubic fluorite-like phases isostructural with Nd5Mo3O16. The atomic structure of a calcium-doped fluorite-like Nd5Mo3O16+δ single crystal grown from an off-stoichiometric melt has been studied by X-ray diffraction. The peculiarities of the structure of calcium-doped fluorite-related compounds were revealed. Experimental structural data demonstrate partial mutual substitutions of Nd and Mo cations, splitting of the O2 position into several additional positions, and the presence of excess oxygen, which occupies octahedral sites in the voids of the structure. Some of the fluorite-like samples have high electrical conductivity, on the order of 10−2 S/cm at 800 C.
Keywords Ceramics; Oxides; Crystal growth; Crystal structure; Ionic conductivity
Remark doi:10.1016/j.jallcom.2016.03.013
Link

Crystal structure and proton conductivity of BaSn0.6Sc0.4O3-δ: Insights from neutron powder diffraction and solid state NMR

Authors Francis Gachau Kinyanjui, Stefan Tommy Norberg, Christopher Knee, Istaq Ahmed, Stephen Hull, Lucienne Buannic, Ivan Hung, Zhehong Gan, Frdric Blanc, Clare P. Grey and Sten Eriksson
Source
Journal of Materials Chemistry A
Time of Publication: 2016
Remark DOI: 10.1039/C5TA09744D
Link

Optically-transparent and electrically-conductive AgI–AgPO3–WO3 glass fibers

Authors Maxime Rioux, Yannick Ledemi, Jeff Viens, Steeve Morency, Seyed Alireza Ghaffari and Youns Messaddeq
Source
RSC Advances
Volume: 5, Pages: 40236-40248
Time of Publication: 2015
Abstract In this study, we report to our knowledge the first optically-transparent and electrically-conductive optical glass fiber belonging to the system AgI–AgPO3–WO3. The addition of tungsten oxide (WO3) into the phosphate glassy network allowed the adjustment of the glass transition temperature, thermal expansion coefficient, refractive index, optical band edge, and electrical conductivity, which are all very important parameters in view of drawing glass fibers with a desired set of electrical and optical properties. Furthermore, the addition of WO3 can improve considerably glass stability against water and humidity in the environment. AgI–AgPO3–WO3 glass fibers with 15 mol% WO3 showed 2 dB m−1 optical propagation loss from 800 to 950 nm wavelength range, and 10−3 S cm−1 electrical conductivity at 1 MHz AC frequency. Complex impedance spectra and thermal activation energies ranging from 0.15 to 0.30 eV are indicative of a dominant conductivity mechanism being ionic in nature within the range of AC frequencies from 1 Hz to 1 MHz. Fibers exhibited higher electrical conductivities than the bulk glasses. Glasses in the AgI–AgPO3–WO3 system can be used for fibers that require a set of adjustable properties pertaining to electrical conductivity, optical transparency, and environmental stability.
Remark DOI: 10.1039/C5RA00681C
Link

Phase Relations and Physical Properties of Layered Pb-Containing Nd2MoO6 Compounds

Authors Valentina Voronkova, Ekaterina Orlova, Sergey Kazakov, Elena Kharitonova and Dmitry Belov
Source
European Journal of Inorganic Chemistry
Volume: 2016, Issue: 7, Pages: 1022-1029
Time of Publication: 2016
Abstract The phase relations along the Nd2MoO6–PbO join of the ternary Nd2O3–MoO3–PbO system have been studied by means of solid-state synthesis in air. The samples with high Pb content underwent a reversible first-order phase transition near 820 C. XRD analysis revealed two tetragonal phases, the high-temperature centric phase (I41/acd) and the low-temperature acentric phase (Iequation image2m). In the region of the phase transition, the permittivity of the Pb-containing samples show a strong lambda-type anomaly and electrical conductivity increases sharply by one and half orders of magnitude. The conductivities of the Pb-containing samples reach 10–2 S/cm at 850 C, which is two orders of magnitude greater than the conductivity of pure Nd2MoO6. The conductivity in such compounds may be due to oxygen ions. A permittivity anomaly, existence of a piezoelectric effect, and the symmetry change from acentric Iequation image2m to centric I41/acd may indicate an antiferroelectric nature of the phase transition.
Keywords Conducting materials;Layered compounds;Lead;Rare earths;Solid-phase synthesis
Remark DOI: 10.1002/ejic.201501167
Link

Phase stability and thermoelectric properties of Cu10.5Zn1.5Sb4S13 tetrahedrite

Authors Subramaniam Harish, Duraisamy Sivaprahasama, Manjusha Battabyal, Raghavan Gopalan
Source
Journal of Alloys and Compounds
Volume: 667, Pages: 323–328
Time of Publication: 2016
Abstract Cu10.5Zn1.5Sb4S13 tetrahedrite compound was prepared by mechanical milling of Cu2S, ZnS and Sb2S3 powders and spark plasma sintered (SPS) to dense samples. The phase formation, chemical homogeneity, thermal stability of the compound and the thermoelectric properties of the sintered samples were evaluated. Single phase tetrahedrite with the crystallite size of 40 nm was obtained after 30 h of milling followed by annealing at 573 K for 6 h in an argon atmosphere. In-situ high-temperature X-ray diffraction studies revealed that the phase is stable up to 773 K. The Seebeck coefficient of the sintered samples of density >98% shows p-type behavior with maximum thermopower of 170 μV/K at 573 K. The electrical resistivity (ρ) decreases with temperature up to 475 K and then increases. A low thermal conductivity of 0.5 W/(m⋅K), in combination with moderate power factor gave a maximum ZT of ∼0.038 at 573 K in Cu10.5Zn1.5Sb4S13 sample having a grain size of ∼200 nm.
Keywords Thermoelectric; Tetrahedrite; Solid state reactions; Spark plasma sintering; Figure of merit
Remark doi:10.1016/j.jallcom.2016.01.094
Link

New ferroelastic K2Sr(MoO4)2: Synthesis, phase transitions, crystal and domain structures, ionic conductivity

Authors Galina D. Tsyrenova, Erzhena Т. Pavlova, Sergey F. Solodovnikov, Nadezhda N. Popova, Tatyana Yu. Kardash, Sergey Yu. Stefanovich, Irina А. Gudkova, Zoya A. Solodovnikova, Bogdan I. Lazoryak
Source
Journal of Solid State Chemistry
Volume: 237, Pages: 64–71
Time of Publication: 2016
Abstract K2Sr(MoO4)2 crystals were synthesized and their properties examined. The distortive polymorphic transformations at 421 K (α (LT)→ β(MT)) and 744 K (β(MT)→γ (HT)) of K2Sr(MoO4)2 were studied. It has been shown that the transitions go in sequence from the high-temperature palmierite K2Pb(SO4)2-type γ-phase (R View the MathML source3m) to an intermediate β-phase with a probable incommensurate structure and then to a low-temperature α-phase. Domain structures peculiarities in ferroelastic α-K2Sr(MoO4)2 have been investigated. The electrical conductivity of K2Sr(MoO4)2 rises tenfold in the vicinity of the phase transition at 744 K that may be associated with a change conductivity path from quasi-one-dimensional to two-dimensional. The crystal structure of the α-phase (sp. gr. С2/c, а=14.318(3) , b=5.9337(12) , с=10.422(2) , β=105.83(3), Z=4, R=0.0219) is similar to that of α-Pb3(PO4)2. Sr-atoms are mainly located at site with the coordination number CN=8 (a tetragonal antiprism with bond lengths of 2.578(2)–2.789(2) ) and K atoms are located at site with CN=9+1.
Keywords Potassium; Strontium; molybdates; Phase transitions; Ferroelastics; Crystal structure; Crystal optics analysis; Domain structure; Ionic conductivity
Remark doi:10.1016/j.jssc.2016.01.011
Link

New methods for the preparation and dielectric properties of Lа2 − xSrxNiO4 (х = 1/8) ceramic

Authors T.I. Chupakhina, N.I. Kadyrova, N.V. Melnikova, O.I. Gyrdasova, E.A. Yakovleva, Yu.G. Zainulin
Source
Materials Research Bulletin
Volume: 77, Pages: 190–198
Time of Publication: 2016
Abstract The perovskite-type oxide La2−xSrxNiO4 (x = 1/8) was prepared by a new precursor route. The reaction proceeds in the self-ignition mode. Single-phase powder and gas-tight ceramic samples can be produced by single annealing of decomposition products. It was shown that as a result of thermobaric treatment of La2−xSrxNiO4 (x = 1/8) the solid solution La2−xSrxNiO4 with a higher concentration of strontium and the second phase La3Ni2O7 are formed. Short-term (5 min) thermobaric treatment (P = 2.5 GPa) at t = 900 С changes the unit cell parameters, but is not accompanied by structural transitions. At the same time, morphological restructuring of the sample occurs—the agglomerates delaminate into thin plates crystals. It was established that the permittivity of the material exposed to thermobaric treatment is much higher compared to that of the sample annealed at atmospheric pressure and virtually does not depend on frequency in a wide temperature range.
Keywords Oxides; X-ray diffraction; High pressure; Impedance spectroscopy; Dielectric properties
Remark doi:10.1016/j.materresbull.2016.01.023
Link

Chemical stability and H2 flux degradation of cercer membranes based on lanthanum tungstate and lanthanum chromite

Authors Jonathan M. Polfus, , Zuoan Li, Wen Xing, Martin F. Sunding, John C. Walmsley, Marie-Laure Fontaine, Partow P. Henriksen, Rune Bredesen
Source
Journal of Membrane Science
Volume: 503, Pages: 42–47
Time of Publication: 2016
Abstract Ceramic–ceramic composite (cercer) membranes of (Mo-doped) lanthanum tungstate, La27(W,Mo)5O55.5−δ, and lanthanum chromite, La0.87Sr0.13CrO3−δ, have recently been shown to exhibit H2 permeabilities among state-of-the-art. The present work deals with the long-term stability of these cercer membranes in line with concern of flux degradation and phase instability observed in previous studies. The H2 permeability of disc shaped membranes with varying La/W ratio in the lanthanum tungstate phase (5.35≤La/W≤5.50) was measured at 900 and 1000 C with a feed gas containing 49% H2 and 2.5% H2O for up to 1500 h. It was observed that the H2 permeability decreased by a factor of up to 5.3 over 1500 h at 1000 C. Post-characterization of the membranes and similarly annealed samples was performed by SEM, STEM and XRD, and segregation of La2O3 was observed. The decrease in H2 permeability was ascribed to the compositional instability of the cation-disordered lanthanum tungstate under the measurement conditions. Equilibration of the La/W ratio by segregation of La2O3 leads to a lower ionic conductivity according to the materials inherent defect chemistry. Partial decomposition and reduction of the lanthanum tungstate phase, presumably to metallic tungsten, was also observed after exposure to nominally dry hydrogen.
Keywords Hydrogen separation; Dense ceramic membrane; Ceramic–ceramic composite; Lanthanum tungstate; Lanthanum chromite
Remark doi:10.1016/j.memsci.2015.12.054
Link

Nb-doped TiO2 sol–gel films for CO sensing applications

Authors M. Duta, L. Predoana, J.M. Calderon-Moreno, S. Preda, M. Anastasescu, A. Marin, I. Dascalu, P. Chesler, C. Hornoiu, M. Zaharescu, P. Osiceanu, M. Gartner
Source
Materials Science in Semiconductor Processing
Volume: 42, Issue: 3, Pages: 397–404
Time of Publication: 2016
Abstract Nb doped titania (TiO2:Nb) multilayered films (1–10 layers) with anatase structure were obtained by the low-cost sol–gel and dipping method on microscope glass substrates, followed by thermal treatment at 450 C for 1 h. After each layer deposition, an intermediate annealing step was performed at 300 C for 30 min. Doping TiO2 sol–gel films with a low amount of Nb (0.8 at%) allows obtaining an improved CO sensor able to operate under environmental atmosphere (air). It was found that the sensor sensitivity is less dependent on the film thickness but is significantly influenced by Nb doping at the optimal working temperature of 400 C. Good recovery characteristics were obtained for a wide CO detection range, between 0 and 2000 ppm. The gas-sensing behavior of the films was correlated with the structural, chemical and morphological properties of the multi-layered structures.
Keywords Sol–gel method; Nb-doped TiO2 films; Microstructure; CO sensor
Remark doi:10.1016/j.mssp.2015.11.004
Link

Synthesis and properties of La0.05Ba0.95Ti1 −xMyO3 (M = Mn, Ce) as anode materials for solid oxide fuel cells

Authors Cdric Prillat-Merceroz, Pascal Roussel, Edouard Capoen, Sbastien Rosini, Patrick Glin, Rose-Nolle Vannier, Gilles Gauthier
Source
Solid State Ionics
Volume: 283, Pages: 21–29
Time of Publication: 2015
Abstract Stoichiometric and sub-stoichiometric lanthanum barium titanates (LBT) of perovskite structure type, substituted or not with Mn and/or Ce at the Ti-site, were prepared by sol–gel route with heat treatment in air. All the compounds display a cubic Pm-3m symmetry, which remains stable in reducing atmosphere. Whereas Mn substitution highly promotes the reducibility of the material, the electrical and electrochemical performance of Mn-doped compounds is decreased with respect to non-doped sub-stoichiometric LBT. In contrast, the electrical conductivity and resistance polarization of Ce-substituted LBT are close to those of non-doped LBT and Ce-substituted LBT appears especially efficient in improving the catalytic properties for methane steam reforming and avoiding carbon formation.
Keywords SOFC; Anode; Perovskite; Barium titanate; Impedance electrochemical spectroscopy; Methane steam reforming
Remark doi:10.1016/j.ssi.2015.11.005
Link

Molybdenum doped Pr0.5Ba0.5MnO3−δ (Mo-PBMO) double perovskite as a potential solid oxide fuel cell anode material

Authors Yi-Fei Sun, Ya-Qian Zhang, Bin Hua, Yashar Behnamian, Jian Li, Shao-Hua Cui, Jian-Hui Lid, Jing-Li Luo
Source
Journal of Power Sources
Volume: 301, Pages: 237–241
Time of Publication: 2016
Abstract A layered Mo doped Pr0.5Ba0.5MnO3−δ (Mo-PBMO) double perovskite oxide was prepared by a modified sol–gel method and the properties of the fabricated material are characterized by various technologies. The results of X-ray diffraction (XRD), H2-temperature programmed reduction (H2-TPR), NH3-temperature programmed desorption (NH3-TPD), and thermogravimetric analysis (TGA) demonstrate that the treatment in reducing atmosphere at high temperature lead to a significant phase transformation of the material to a single cubic phase as well as with the Mo in multiple oxidized states. Such character leads to the production of large amount of oxygen deficiency with facilitated oxygen diffusion. The electrochemical performance tests of half-cell and single cell SOFCs exhibit the promoted effect of Mo on catalytic activity for the oxidation of H2 and CH4, indicating that Mo-PBMO could serve as an anode material candidate for SOFCs.
Keywords Mo; Pr0.5Ba0.5MnO3−δ; Double perovskite; Anode; SOFC
Remark doi:10.1016/j.jpowsour.2015.09.127
Link

Experimental and molecular dynamics study of thermo-physical and transport properties of ThO2-5wt.%CeO2 mixed oxides

Authors P.S. Somayajulu, P.S. Ghosh, J. Banerjee, K.L.N.C. Babu, K.M. Danny, B.P. Mandal, T. Mahata, P. Sengupta, S.K. Sali, A. Arya
Source
Journal of Nuclear Materials
Volume: 467, Issue: 2, Pages: 644–659
Time of Publication: 2015
Abstract We have determined the thermo-physical (elastic modulus, specific heat, thermal expansion and thermal conductivity) and transport (ionic conductivity) properties of ThO2-5wt.%CeO2 mixed oxide (MOX) using a combined experimental and theoretical methodology. The specific heat, ionic conductivity and elastic properties of ThO2-5wt.%CeO2 pellets prepared by conventional powder metallurgy (POP) and coated agglomerate pelletization (CAP) routes (sintered in both air and Ar-8%H2 atmosphere) are compared with respect to homogeneity (CeO2 distribution in ThO2 matrix), microstructure, porosity and oxygen to metal ratio. The effects of inhomogeneity and pore distribution on thermal expansion and thermal conductivity of the mixed-oxide pellets are identified. Molecular dynamics (MD) simulations using the Coulomb-Buckingham-Morse-many-body model based interatomic potentials are used to predict elastic properties in the temperature range between 300 and 2000 K and thermodynamic properties, viz., enthalpy increment and specific heats of ThO2. Finally, the thermal expansion coefficient and thermal conductivity of ThO2 and (Th,Ce)O2 mixed-oxides obtained from MD are compared with available experimental results.
Keywords ThO2-5%CeO2 MOX; Specific heat; Ionic conductivity; Temperature dependent elastic properties; Molecular dynamics simulation
Remark doi:10.1016/j.jnucmat.2015.10.053
Link

Effect of Cerium on the Electrical Properties of a Cobalt Conversion Coating for Solid Oxide Fuel Cell Interconnects – A Study Using Impedance Spectroscopy

Authors Jan Gustav Grolig, Jan Froitzheim, Jan-Erik Svensson
Source
Electrochimica Acta
Volume: 184, Pages: 301–307
Time of Publication: 2015
Abstract Coatings of metallic cobalt, which convert into a cobalt manganese spinel oxide are known to improve the properties of interconnects for solid oxide fuel cells (SOFCs). The addition of cerium to the cobalt coating further improves the corrosion properties of the material. For this study traditional four-point DC measurements at high temperatures were combined with impedance spectroscopy at low temperatures in order to investigate the effect of cerium on the electrical properties of a cobalt conversion coating. It was found that combination-coatings of cerium and cobalt exhibit superior electrical properties compared to pure cobalt coatings. Cerium slows down the growth of chromia and prevents the outward diffusion of iron into the cobalt spinel layer. Both effects are beneficial for the electrical properties of the interconnect. Impedance spectroscopy measurements revealed that even after more than 3000 h of exposure the outer cobalt manganese spinel layer still has a higher electrical conductivity when cerium was present.
Remark doi:10.1016/j.electacta.2015.10.111
Link

Lithium Polymer Electrolytes Based on Sulfonated Poly(ether ether ketone) for Lithium Polymer Batteries

Authors Savitha Thayumanasundaram, Vijay Shankar Rangasamy, Jin Won Seo andJean-Pierre Locquet
Source
European Journal of Inorganic Chemistry
Volume: 2015, Issue: 32, Pages: 5395–5404
Time of Publication: 2015
Abstract We studied a lithium-ion conducting polymer based on sulfonated poly(ether ether ketone) (SPEEK) doped with lithium bis(trifluoromethane)sulfonimide (LiTFSI). Self-standing membranes were prepared by the solvent-casting technique with a LiTFSI loading of 0 to 30 wt.-%. The thermogravimetric analysis curves showed that the SO3H groups decompose earlier in the SPEEK–LiTFSI membranes than in pure SPEEK, owing to interactions between the Li+ ions and the SO3H groups. X-ray diffraction and differential scanning calorimetry studies showed that the addition of LiTFSI decreased the crystallinity and the glass-transition temperature of the polymer, which revealed the plasticizing effect of the lithium salt on the polymer matrix. The 7Li NMR spectroscopy results showed a single central transition line at around δ = –1.2 ppm, which indicated the presence of free mobile lithium ions. Dynamic mechanical analysis of the membrane showed it to be mechanically stable up to 100 C, a prerequisite for flexible lithium polymer batteries. The highest room-temperature conductivity in the order of 10–5 S cm–1 was observed for the 20 wt.-% LiTFSI-doped SPEEK membrane, which increased to 5  10–4 S cm–1 at 100 C.
Keywords Lithium batteries;Polymer electrolytes;Dynamic mechanical analysis;Raman spectroscopy;Ion pairs
Remark DOI: 10.1002/ejic.201500649
Link

Exceptional hydrogen permeation of all-ceramic composite robust membranes based on BaCe0.65Zr0.20Y0.15O3−δ and Y- or Gd-doped ceria

Authors Elena Rebollo, Cecilia Mortal, Sonia Escolstico, Stefano Boldrini, Simona Barison, Jos M. Serra and Monica Fabrizio
Source
Energy Environ. Sci.
Volume: 8, Pages: 3675-3686
Time of Publication: 2015
Abstract Mixed proton and electron conductor ceramic composites were examined as hydrogen separation membranes at moderate temperatures (higher than 500 C). In particular, dense ceramic composites of BaCe0.65Zr0.20Y0.15O3−δ (BCZ20Y15) and Ce0.85M0.15O2−δ (M = Y and Gd, hereafter referred to as YDC15 and GDC15), as protonic and electronic conducting phases respectively, were successfully prepared and tested as hydrogen separation membranes. The mixture of these oxides improved both chemical and mechanical stability and increased the electronic conductivity in dual-phase ceramic membranes. The synthetic method and sintering conditions were optimized to obtain dense and crack free symmetric membranes. The addition of ZnO as a sintering aid allowed achieving robust and dense composites with homogeneous grain distribution. The chemical compatibility between the precursors and the influence of membrane composition on electrical properties and H2 permeability performances were thoroughly investigated. The highest permeation flux was attained for the 50 : 50 volume ratio BCZ20Y15–GDC15 membrane when the feed and the sweep sides of the membrane were hydrated, reaching values of 0.27 mL min−1 cm−2 at 755 C on a 0.65 mm thick membrane sample, currently one of the highest H2 fluxes obtained for bulk mixed protonic–electronic membranes. Increasing the temperature to 1040 C, increased the hydrogen flux up to 2.40 mL min−1 cm−2 when only the sweep side was hydrated. The H2 separation process is attributed to two cooperative mechanisms, i.e. proton transport through the membrane and H2 production via the water splitting reaction coupled with oxygen ion transport. Moreover, these composite systems demonstrated a very good chemical stability under a CO2-rich atmosphere such as catalytic reactors for hydrogen generation.
Remark DOI: 10.1039/C5EE01793A
Link

The effect of Cu2O nanoparticle dispersion on the thermoelectric properties of n-type skutterudites

Authors M Battabyal, B Priyadarshini, D Sivaprahasam, N S Karthiselva and R Gopalan
Source
Journal of Physics D: Applied Physics
Volume: 48, Issue: 45 Time of Publication: 2015
Abstract We report the thermoelectric properties of Ba0.4Co4Sb12 and Sn0.4Ba0.4Co4Sb12 skutterudites dispersed with Cu2O nanoparticles. The samples were synthesized by ball milling and consolidated by spark plasma sintering. Dispersion of Cu2O is found to significantly influence the electrical resistivity and thermopower at high temperatures with a more pronounced effect on the electrical resistivity due to the energy filtering effect at the interface between Cu2O nanoparticles and a Ba0.4Co4Sb12 and Sn0.4Ba0.4Co4Sb12 matrix. At 573 K, the electrical resistivity of Ba0.4Co4Sb12 decreases from 5.01    10−5 Ωm to 2.98    10−5 Ωm upon dispersion of Cu2O. The dispersion of Cu2O reduces the thermal conductivity of the samples from 300 K and above by increasing the phonon scattering. The lowest observed thermal conductivity at 573 K is found to be 2.001 W mK−1 in Cu2O dispersed Ba0.4Co4Sb12 while it is 2.91 W mK−1 in the Ba0.4Co4Sb12 sample without Cu2O dispersion. Hence Cu2O dispersion plays a significant role in the thermoelectric properties and a maximum figure of merit (ZT ) ~ 0.92 is achieved in Cu2O dispersed Ba0.4Co4Sb12 at 573 K which is more than 200% compared to the pure Ba0.4Co4Sb12 sample. The results from nanoindentation experiments show that the Cu2O dispersed sample (Cu2O  +  Sn0.4Ba0.4Co4Sb11.6) has a higher reduced Youngs modulus (~139 GPa) than the pure Sn0.4Ba0.4Co4Sb11.6 sample (~128 GPa).
Remark Link

Oxygen permeation and creep behavior of Ca1−xSrxTi0.6Fe0.15Mn0.25O3−δ (x=0, 0.5) membrane materials

Authors Jonathan M. Polfus, Wen Xing, Goran Pećanac, Anita Fossdal, Sidsel M. Hanetho, Yngve Larring, Jrgen Malzbender, Marie-Laure Fontaine, Rune Bredesen
Source
Journal of Membrane Science
Volume: 449, Pages: 172–178
Time of Publication: 2016
Abstract Oxygen permeation measurements were performed on dense symmetric samples of Ca0.5Sr0.5Ti0.6Fe0.15Mn0.25O3−δ and compared to CaTi0.6Fe0.15Mn0.25O3−δ in order to assess the influence of the perovskite lattice volume on oxygen permeation. Oxygen flux measurements were performed in the temperature range 700–1000 C and as function of feed side pO2pO2 from 10−2 to 1 bar, and at high pressures up to 4 bar with a pO2pO2 of 3.36 bar. The O2 permeability of the Sr-doped sample was significantly lower than that of the Sr-free sample, amounting to 3.910−3 mL min−1 cm−1 at 900 C for a feed side pO2pO2 of 0.21 bar. The O2 permeability of CaTi0.6Fe0.15Mn0.25O3−δ shows little variation with increased feed side pressures and reaches 1.510−2 mL min−1 cm−1 at 900 C for a feed side pO2pO2 of 3.36 bar. This is approximately 1.5 times higher than the O2 permeability with a feed side pO2pO2 of 0.21 bar. Furthermore, in order to assess the applicability of CaTi0.6Fe0.15Mn0.25O3−δ as an oxygen membrane material, creep tests were performed under compressive loads of 30 and 63 MPa, respectively, in air in the temperature range 700–1000 C; the results indicate a high creep resistance for this class of materials. The measured O2 permeabilities and creep rates are compared with other state-of-the-art membrane materials and their performance for relevant applications is discussed in terms of chemical and mechanical stability.
Keywords Dense ceramic oxygen membrane; Ambipolar transport; Creep; CaTiO3; Calcium titanate
Remark doi:10.1016/j.memsci.2015.10.016
Link

Comparative study of the electrochemical promotion of CO2 hydrogenation on Ru using Na+, K+, H+ and O2 − conducting solid electrolytes

Authors I. Kalaitzidou, M. Makri, D. Theleritis, A. Katsaounis, C.G. Vayenas
Source
Surface Science
Time of Publication: 2015
Abstract The kinetics and the electrochemical promotion of the hydrogenation of CO2 to CH4 and CO are compared for Ru porous catalyst films deposited on Na+, K+, H+ and O2 − conducting solid electrolyte supports. It is found that in all four cases increasing catalyst potential and work function enhances the methanation rate and selectivity. Also in all four cases the rate is positive order in H2 and exhibits a maximum with respect to CO2. At the same time the reverse water gas shift reaction (RWGS) which occurs in parallel exhibits a maximum with increasing pH2pH2 and is positive order in CO2. Also in all cases the selectivity to CH4 increases with increasing pH2pH2 and decreases with increasing pCO2pCO2. These results provide a lucid demonstration of the rules of chemical and electrochemical promotion which imply that (∂r/∂Φ)(∂r/∂pD) > 0 and (∂r/∂Φ)(∂r/∂pA) < 0, where r denotes a catalytic rate, Φ is the catalyst work function and pD and pA denote the electron donor and electron acceptor reactant partial pressures respectively.
Keywords Effect of Ru catalyst support and potential on product selectivity.
Remark In Press, doi:10.1016/j.susc.2015.09.011
Link

Electrochemical promotion of the hydrogenation of CO2 on Ru deposited on a BZY proton conductor

Authors I. Kalaitzidou, A. Katsaounis, T. Norby, C.G. Vayenas
Source
Journal of Catalysis
Volume: 331, Pages: 98–109
Time of Publication: 2015
Abstract he kinetics and the electrochemical promotion of the hydrogenation of CO2 on polycrystalline Ru deposited on BZY (BaZr0.85Y0.15O3−α + 1 wt% NiO), a proton conductor in wet atmospheres, with α ≈ 0.075, was investigated at temperatures 300–450 C and atmospheric pressure. Methane and CO were the only detectable products and the selectivity to CH4 could be reversibly controlled between 15% and 65% by varying the catalyst potential by less than 1.2 V. The rate and the selectivity to CH4 are very significantly enhanced by proton removal from the catalyst via electrochemically controlled spillover of atomic H from the catalyst surface to the proton-conducting support. The effect is strongly non-Faradaic and the apparent Faradaic efficiency of methanation takes values up to 500 and depends strongly on the porous Ru catalyst film thickness. The observed strong promotional effect, in conjunction with the observed reaction kinetics, is in good agreement with the rules of electrochemical and chemical promotion.
Keywords Hydrogenation of CO2; CO2 methanation; Ru catalyst; RWGS reaction; BZY proton conducting support; Selectivity modification; Electrochemical promotion of catalysis (EPOC); Non-faradaic electrochemical modification of catalytic activity (NEMCA effect)
Remark doi:10.1016/j.jcat.2015.08.023
Link

Electrochemical Promotion of Ir0.5Pt0.5O2/YSZ

Authors S. Balomenou, K. M. Papazisi, D. Tsiplakides
Source
Topics in Catalysis
Volume: 58, Issue: 18, Pages: 1270-1275
Time of Publication: 2015
Abstract A high surface area, nanostructured bimetallic oxide catalyst, Ir0.5Pt0.5O2, deposited on YSZ was studied for the electrochemical promotion of ethylene oxidation. The catalyst was synthesized using the modified Adams fusion method and was characterized regarding its structure, morphology and specific surface area via XPS, XRD, HRTEM, SEM and BET. Regarding the performance for electrochemical promotion, it was found that the rate of ethylene oxidation can be enhanced significantly and in a strongly non-faradaic manner via positive potential application, exhibiting strongly electrophobic behaviour.
Keywords Electrochemical promotion, EPOC, Ir0.5Pt0.5O2, Adams fusion method
Remark Link

Enhanced Carbon Deposition Tolerance of SOFC Anodes Under Triode Operation

Authors Ioanna Petrakopoulou, Dimitrios Tsiplakides, Stella Balomenou
Source
Topics in Catalysis
Volume: 58, Issue: 18, Pages: 1303-1310
Time of Publication: 2015
Abstract The triode fuel cell design and operation concept was applied as an alternative means for controlling and enhancing the carbon tolerance of state-of-the-art solid oxide fuel cell (SOFC) anodes. The triode cell configuration entails the introduction of a third electrode in addition to the anode and cathode, driven by an auxiliary circuit which is run in electrolytic mode. In this way the cell is forced to operate at controlled potential differences that are inaccessible under standard operation, and thus introduces a controllable variable into fuel cell operation. In the present study, the effectiveness of the triode approach was evaluated for the in situ control of the rate of carbon deposition in commercial multilayer NiO–GDC and NiO–YSZ SOFC anodes. The study involved typical and triode operation of SOFC button cells under CH4 steam reforming conditions, and it was found that the application of a small electrolytic current under triode operation resulted in significantly less carbon built-up on the anode compared to the standard SOFC operation.
Keywords SOFC Triode fuel cell operation, Anode degradation, Carbon formation, CH4 steam reforming
Remark Link

Development of a Coking-Resistant NiSn Anode for the Direct Methane SOFC

Authors N. Bogolowski, B. Iwanschitz and J.-F. Drillet
Source
Fuel Cells
Volume: 15, Issue: 5, Pages: 711–717
Abstract The present work reports on the development of a coking-resistant NiSn-based membrane electrode assembly (MEA) for internal CH4 reforming in solid oxide fuel cells (SOFCs). Catalyst powder was prepared in a centrifugal casting oven by melting stoichiometric amounts of Ni and Sn under vacuum. The formation of Ni3Sn2 intermetallic phase was confirmed by XRD analysis. Catalytic activity for CH4 reforming and stability of the NiSn powder were first evaluated in a quartz glass reactor for 4 h at 600–1,000 C. The main reaction products H2 and CO were detected by gas chromatography while no carbon formation was detected during the experiments. Then, 3YSZ electrolyte-supported MEAs were fabricated with a Ni3Sn2/YSZ anode and LSM/YSZ cathode and characterized under SOFC conditions. The MEA showed an excellent stability under CH4 atmosphere (3% H2O) at 850 C over more than 650 h. No substantial decrease in cell potential was observed during this period.
Keywords Anode Material;Intermetallic Phase;Internal Reforming;Methane;Nickel-Tin Alloy;Ni3Sn2;SOFC;Solid Oxide Fuel Cell
Remark DOI: 10.1002/fuce.201400187
Link

Hardening in non-stoichiometric (1−x)Bi0.5Na0.5TiO3–xBaTiO3 lead-free piezoelectric ceramics

Authors Sasiporn Prasertpalichat, David P. Cann
Source
Journal of Materials Science
Volume: 51, Issue: 1, Pages: 476-486
Time of Publication: 2016
Abstract The role of A-site non-stoichiometry was investigated in lead-free piezoelectric ceramics based on compositions in the 1 − x(Bi0.5Na0.5TiO3)–xBaTiO3 system near the morphotropic phase boundary, where x = 0.055, 0.06, and 0.07. Donor doping was introduced through the addition of excess Bi, however, there were no changes in the crystal structure. In contrast, acceptor doping was introduced through the addition of excess Na and was found to promote rhombohedral distortions. A significant improvement of dielectric properties was observed in donor-doped compositions and, in contrast, a degradation in properties was observed in acceptor-doped compositions. Compared to the stoichiometric composition, the acceptor-doped compositions displayed a significant increase in coercive field (E c) which is an indication of domain wall pinning as found in hard Pb(Zr x Ti1−x )O3. This result was further confirmed via remanent polarization hysteresis analyses. Moreover, all A-site acceptor-doped compositions also exhibited an increase in mechanical quality factor (Q m) as well as a decrease in piezoelectric coefficient (d 33), dielectric loss (tan δ), remanent polarization (P r), and dielectric permittivity, which are all the typical characteristics of the effects of “hardening.” The mechanism for the observed hardening in A-site acceptor-doped BNT-based systems is linked to changes in the long-range domain structure and defect chemistry.
Remark Link

Copper Iron Conversion Coating for Solid Oxide Fuel Cell Interconnects

Authors Jan Gustav Grolig, , Patrik Alnegren, Jan Froitzheim, Jan-Erik Svensson
Source
Journal of Power Sources
Volume: 297, Pages: 534–539
Time of Publication: 2015
Abstract A conversion coating of iron and copper was investigated with the purpose of increasing the performance of Sanergy HT as a potential SOFC interconnect material. Samples were exposed to a simulated cathode atmosphere (air, 3 % H2O) for durations of up to 1000 h at 850 C. Their performance in terms of corrosion, chromium evaporation and electrical resistance (ASR) was monitored and compared to uncoated and cobalt-coated Sanergy HT samples. The copper iron coating had no negative effects on corrosion protection and decreased chromium evaporation by about 80%. An Area Specific Resistance (ASR) of 10 mΩcm2 was reached after 1000 h of exposure. Scanning Electron Microscopy revealed well adherent oxide layers comprised of an inner chromia layer and an outer spinel oxide layer.
Keywords Interconnect; Corrosion; Chromium volatilization; Sanergy HT; SOFC; Area specific resistance
Remark doi:10.1016/j.jpowsour.2015.06.139
Link

Atomic structure and ionic conductivity of glassy materials based on silver sulfide

Authors N. V. Melnikova, K. V. Kurochka, O. L. Kheifets, N. I. Kadyrova, Ya. Yu. Volkova
Source
Volume: 79, Issue: 6, Pages: 719-722
Time of Publication: 2015
Abstract The effect of the composition of glassy ionic conductors AgGe1 + x As1–x S3 and the composites based on these materials containing single-walled carbon nanotubes (CNT) AgGe1+x As1–x (S + CNT)3, on the atomic structure and ionic conductivity is analyzed.
Remark Link

Protons in piezoelectric langatate; La3Ga5.5Ta0.5O14

Authors Tor Svendsen Bjrheim, Vijay Shanmugappirabu, Reidar Haugsrud, Truls E. Norby
Source
Solid State Ionics
Volume: 278, Pages: 275–280
Time of Publication: 2015
Abstract This contribution reports the hydration and electrical transport properties of effectively acceptor doped single crystalline and polycrystalline langatate, La3Ga5.5Ta0.5O14. The electrical properties are investigated over wide ranges of pH2OpH2O, pD2OpD2O and pO2pO2 in the temperature range 400 to 1000 C. Acceptor doped langatate is dominated by oxygen vacancies in dry atmospheres and at high temperatures, and by protonic defects in wet atmospheres and at lower temperatures. The corresponding standard hydration enthalpy and entropy are − 90 5 kJ/mol and − 130 5 J/mol K, respectively. Further, all compositions display pure proton conductivity in wet atmospheres below 700 C with a proton mobility enthalpy in the range of 70–75 kJ/mol, depending on doping level and crystallographic direction. Hence, protons are important for the physiochemical properties of langatate even at 1000 C, and could therefore influence the behavior of langatate-based resonator devices. The proton conductivity is slightly anisotropic, being higher in the X- and Y- than in the Z-direction. At high temperatures and under dry conditions, electron holes and oxide ions dominate the conductivity, and the enthalpy of mobility of vacancies is 140 5 kJ/mol.
Keywords Langatate; Piezoelectric; Defects; Protons; Conductivity
Remark doi:10.1016/j.ssi.2015.06.024
Link

Tetragonal tungsten bronzes Nb8−xW9+xO47−δ: optimization strategies and transport properties of a new n-type thermoelectric oxide

Authors Christophe P. Heinrich, Matthias Schrade, Giacomo Cerretti, Ingo Lieberwirth, Patrick Leidich, Andreas Schmitz, Harald Fjeld, Eckhard Mueller, Terje G. Finstad, Truls Norby and Wolfgang Tremel
Source
Materials Horizons
Issue: 5, Pages: 519-527
Time of Publication: 2015
Abstract Engineering of nanoscaled structures may help controlling the electrical and thermal transport in solids, in particular for thermoelectric applications that require the combination of low thermal conductivity and low electrical resistivity. The tetragonal tungsten bronzes Nb8−xW9+xO47 (TTB) allow a continuous variation of the charge carrier concentration while fulfilling at the same time the concept of a “phonon-glass electron-crystal” through a layered nanostructure defined by intrinsic crystallographic shear planes. The thermoelectric properties of the tetragonal tungsten bronzes Nb8−xW9+xO47−δ (0 < x < 2) were studied in the temperature range from 373 to 973 K. Structural defects and the thermal stability under various oxygen partial pressure pO2 were investigated by means of thermogravimetry, HR-TEM, and XRD. Nb8W9O47−δ was found stable at 973 K and a pO2 of ≈10−15 atm. The oxygen nonstoichiometry δ can reach up to 0.3, depending on the applied atmosphere. By increasing the substitution level x, the electrical resistivity ρ and the Seebeck coefficient S decreased. For x = 2, ρ reached 20 mΩ cm at 973 K, combined with a Seebeck coefficient of approximately −120 μV K−1. The thermal conductivity was low for all samples, ranging from 1.6 to 2.0 W K−1 m−1, attributed to the complex crystal structure. The best thermoelectric figure of merit zT of the investigated samples was 0.043, obtained for x = 2 at 973 K, but it is expected to increase significantly upon a further increase of x. The control of the oxygen non-stoichiometry δ opens a second independent optimization strategy for tetragonal tungsten bronzes.
Remark DOI: 10.1039/C5MH00033E
Link

EuBaCo2O5+δ-Ce0.9Gd0.1O2−δ composite cathodes for intermediate-temperature solid oxide fuel cells: high electrochemical performance and oxygen reduction kinetics

Authors Zhan Shi, Tian Xia, Fuchang Meng, Jingping Wang, Shengming Wu, Jie Lian, Hui Zhao, Chunbo Xu
Source
Electrochimica Acta
Volume: 174, Pages: 608–614
Time of Publication: 2015
Abstract The characteristics and electrochemical performance of double perovskite EuBaCo2O5+δ (EBCO) have been investigated as a composite cathode for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The thermal expansion coefficients can be effectively reduced in the case of EBCO-Ce0.9Gd0.1O2−δ (CGO) composite cathodes. No chemical reactions between EBCO cathode and CGO electrolyte are observed after sintering at 1000 C for 24 h. The maximum electrical conductivities of EBCO-CGO materials reach 28-77 S cm−1 with the change of CGO weight ratio from 40 wt. % to 5 wt. %. Among all these components, the EBCO-10 wt. % CGO (EBCO-10CGO) composite cathode gives the lowest area-specific resistance of 0.055 and 0.26 Ω cm2 in air at 700 and 600 C, respectively. The maximum power density of Ni-CGO anode-supported single cell consisted of the EBCO-10CGO composite cathode and CGO electrolyte achieves 0.81 W cm−2 at 700 C. These results indicate that the EBCO-10CGO composite materials can be used as a promising cathode candidate for IT-SOFCs. Furthermore, the rate-limiting steps for the oxygen reduction reaction at the EBCO-10CGO composite cathode interface are determined to be the charge transfer and dissociation of adsorbed molecule oxygen processes.
Keywords Intermediate-temperature solid oxide fuel cells; cathode materials; electrochemical performance; oxygen reduction kinetics
Remark doi:10.1016/j.electacta.2015.06.059
Link

Multilayer ceramic capacitors based on relaxor BaTiO3-Bi(Zn1/2Ti1/2)O3 for temperature stable and high energy density capacitor applications

Authors Nitish Kumar, Aleksey Ionin, Troy Ansell, Seongtae Kwon, Wesley Hackenberger and David Cann
Source
Applied Physics Letters
Volume: 106, Pages: 252901
Time of Publication: 2015
Abstract The need for miniaturization without compromising cost and performance continues to motivate research in advanced capacitor devices. In this report, multilayerceramiccapacitors based on relaxor BaTiO3-Bi(Zn1/2Ti1/2)O3 (BT-BZT) were fabricated and characterized. In bulk ceramic embodiments, BT-BZT has been shown to exhibit relative permittivities greater than 1000, high resistivities (ρ > 1 GΩ-cm at 300 C), and negligible saturation up to fields as high as 150 kV/cm. Multilayercapacitor embodiments were fabricated and found to exhibit similar dielectric and resistivity properties. The energy density for the multilayerceramics reached values of ∼2.8 J/cm3 at room temperature at an applied electric field of ∼330 kV/cm. This represents a significant improvement compared to commercially available multilayercapacitors. The dielectric properties were also found to be stable over a wide range of temperatures with a temperature coefficient of approximately −2000 ppm/K measured from 50 to 350 C, an important criteria for high temperature applications. Finally, the compatibility of inexpensive Ag-Pd electrodes with these ceramics was also demonstrated, which can have implications on minimizing the device cost.
Remark http://dx.doi.org/10.1063/1.4922947
Link

Electrical conductivity of Zn-doped high temperature proton conductor LaNbO4

Authors Yong Cao, Yuan Tan, Dong Yan, , Bo Chi, Jian Pu, Li Jian
Source
Solid State Ionics
Volume: 278, Pages: 152–156
Time of Publication: 2015
Abstract Zn-doped LaNbO4 (La1 − xZnxNbO4 − δ, LZ100x) was prepared by a solid-state reaction method with x = 0, 0.005, 0.01, 0.015, 0.03 and 0.05 and investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and conductivity measurement. There were no XRD and TEM evidences of formed secondary phases in the composition range of x ≤ 0.03 due to the sensitivity. However, the solubility of Zn, less than 1.0 mol.%, was reasonable, according the variety of the grain sizes, conductivity, as well as the activation energy for the conductivity, with the increasing concentration of Zn. The conductivity of LaNbO4 was improved by one to two orders of magnitude with Zn doping in the research range; and the highest conductivity of 9.8 10− 4 S cm− 1 was obtained with LZ0.5 at 900 C in wet air.
Keywords LaNbO4; Conductivity; Zn doping; Grain size
Remark doi:10.1016/j.ssi.2015.06.011
Link

Gd- and Pr-based double perovskite cobaltites as oxygen electrodes for proton ceramic fuel cells and electrolyser cells

Authors Ragnar Strandbakke, Vladimir A. Cherepanov, Andrey Yu. Zuev, Dmitry S. Tsvetkov, Christos Argirusis, Georgia Sourkouni, Stephan Prnte, Truls Norby
Source
Solid State Ionics
Volume: 278, Pages: 120–132
Time of Publication: 2015
Abstract Double perovskite oxides BaGd0.8La0.2Co2O6−δ (BGLC), BaGdCo1.8Fe0.2O6−δ (BGCF), BaPrCo2O6−δ (BPC) and BaPrCo1.4Fe0.6O6−δ (BPCF) were investigated as oxygen electrodes on mixed conducting BaZr0.7Ce0.2Y0.1O3 (BZCY72) electrolyte using impedance spectroscopy vs temperature, pO2, and pH2O. We propose and have applied a novel approach to extract and parameterise the charge transfer and diffusion impedances of the electrode reactions in a system comprising charge transport of protons, oxide ions, and electrons. Given by the properties of the BZCY72, transport of protons dominates at lower temperatures and high pH2O, oxide ions at higher temperatures, and electron holes increasingly at high temperatures and high pO2. The electrodes showed good performance, with the lowest total apparent polarisation resistance for BGLC/BZCY72 being 0.05 and 10 Ωcm2 at 650 and 350 C, respectively. The low temperature rate limiting reaction step is a surface related process, involving protonic species, with an activation energy of approximately 50 kJ mol−1 for BGLC/BZCY72. The oxide ion transport taking over at higher temperatures exhibits a higher activation energy typical of SOFC cathodes. Thermogravimetric studies revealed that BGLC exhibits considerable protonation at 300–400 C, which may be interpreted as hydration with an enthalpy of approximately –50 kJ mol−1. The resulting mixed proton electron conduction may explain its good performance as electrode on BZCY72.
Keywords PCFC; PCEC; P-MIEC; Proton conductor; Mixed conductivity; Double perovskite
Remark doi:10.1016/j.ssi.2015.05.014
Link

Praseodymium-deficiency Pr0.94BaCo2O6-δ double perovskite: A promising high performance cathode material for intermediate-temperature solid oxide fuel cells

Authors Fuchang Meng, Tian Xia, Jingping Wang, Zhan Shi, Hui Zhao
Source
Journal of Power Sources
Volume: 239, Pages: 741–750
Time of Publication: 2015
Abstract Praseodymium-deficiency Pr0.94BaCo2O6-δ (P0.94BCO) double perovskite has been evaluated as a cathode material for intermediate-temperature solid oxide fuel cells. X-ray diffraction pattern shows the orthorhombic structure with double lattice parameters from the primitive perovskite cell in Pmmm space group. P0.94BCO has a good chemical compatibility with Ce0.9Gd0.1O1.95 (CGO) electrolyte even at 1000 C for 24 h. It is observed that the Pr-deficiency can introduce the extra oxygen vacancies in P0.94BCO, further enhancing its electrocatalytic activity for oxygen reduction reaction. P0.94BCO demonstrates the promising cathode performance as evidenced by low polarization are-specific resistance (ASR), e. g. 0.11 Ω cm2 and low cathodic overpotential e. g. −56 mV at a current density of −78 mA cm−2 at 600 C in air. These features are comparable to those of the benchmark cathode Ba0.5Sr0.5Co0.8Fe0.2O3-δ. The fuel cell CGO-Ni|CGO|P0.94BCO presents the attractive peak power density of 1.05 W cm−2 at 600 C. Furthermore, the oxygen reduction kinetics of P0.94BCO material is also investigated, and the rate-limiting steps for oxygen reduction reaction are determined.
Keywords Intermediate-temperature solid oxide fuel cell; Cathode material; Double perovskite; Electrochemical performance; Oxygen reduction reaction
Remark doi:10.1016/j.jpowsour.2015.06.007
Link

Reduced long term electrical resistance in Ce/Co-coated ferritic stainless steel for solid oxide fuel cell metallic interconnects

Authors Anna Magrasa, Hannes Falk-Windisch, Jan Froitzheim, Jan-Erik Svensson, Reidar Haugsrud
Source
International Journal of Hydrogen Energy
Volume: 40, Issue: 27, Pages: 8579–8585
Abstract The present study is focused on the influence of selected coatings on a ferritic stainless steel (Sanergy HT™, Sandvik) on the evolution of the area specific resistance (ASR) as a function of time at high temperature. The samples are exposed in humidified air at 850 C for up to 4200 h. It combines long-term ASR measurements with the thermogravimetric behavior and microstructural analysis of the cross sections by scanning electron microscopy. The results show that uncoated and Co-coated Sanergy HT™ exhibit similar oxidation kinetics and comparable ASRs, while a combined Ce/Co coating improves oxidation resistance and, consequently, reduces the ASR significantly. Other reports have earlier shown that Co- (and Ce/Co)-coated Sanergy HT™ reduces the evaporation of volatile chromium species. Overall, the study indicates that Ce/Co-coatings will render substantially improved performance for ferritic steel interconnects for solid oxide fuel cells.
Keywords Metallic coating; SOFC; Interconnects; Stainless steel; Conductivity; ASR
Remark doi:10.1016/j.ijhydene.2015.04.147
Link

Resistivity Enhancement and Transport Mechanisms in (1 − x)BaTiO3–xBi(Zn1/2Ti1/2)O3 and (1 − x)SrTiO3–xBi(Zn1/2Ti1/2)O3

Author Nitish Kumar* andDavid P. Cann
Source
Journal of the American Ceramic Society
Time of Publication: 2015
Abstract Ceramics of composition (1−x)BaTiO3–xBi(Zn1/2Ti1/2)O3 (BT-BZT) were prepared by solid-state synthesis; they have been shown to exhibit excellent properties suited for high-temperature dielectric applications. The X-ray diffraction data showed a single-phase perovskite structure for all the compositions prepared (x ≤ 0.1 BZT). The compositions with less than 0.075 BZT exhibited tetragonal symmetry at room temperature and pseudo-cubic symmetry above it. Most notably, a significant improvement in insulation properties was measured with the addition of BZT. Both low-field AC impedance and high-field direct DC measurements indicated an increase in resistivity of at least two orders of magnitude at 400C with the addition of just 0.03 BZT (~107 Ω-cm) into the solid solution as compared to pure BT (~105 Ω-cm). This effect was also evident in dielectric loss data, which remained low at higher temperatures as the BZT content increased. In conjunction with band gap measurements, it was also concluded that the conduction mechanism transitioned from extrinsic for pure BT to intrinsic for 0.075 BZT suggesting a change in the fundamental defect equilibrium conditions. It was also shown that this improvement in insulation properties was not limited to BT-BZT, but could also be observed in the paraelectric SrTiO3–BZT system.
Remark DOI: 10.1111/jace.13666, Article first published online
Link

Triode operation for enhancing the performance of H2S-poisoned SOFCs operated under CH4–H2O mixtures

Authors Foteini M. Sapountzi, Michail N. Tsampas, Chunhua Zhao, Antoinette Boreave, Laurence Retailleau, Dario Montinaro, Philippe Vernoux
Source
Solid State Ionics
Volume: 277, Pages: 65–71
Time of Publication: 2015
Abstract Performances of Solid Oxide Fuel Cells (SOFCs) were investigated in triode operation mode under methane steam reforming in the presence of H2S. Both the catalytic performances for methane steam reforming and the electrochemical properties for the electrochemical oxidation of hydrogen of a Ni/GDC anode drastically dropped in the presence of 1 ppm H2S. Poisoned catalytic sites are different from those for the hydrogen electrochemical oxidation. Triode operation, i.e. application of moderate negative currents between the anode and an auxiliary electrode, can improve electrochemical properties, as a result of a local production of H2 coming from H2O electrolysis. Some specific triode operations were found to achieve a thermodynamic efficiency close to the unity to avoid any energy overconsumption.
Keywords SOFC; Triode operation; H2S poisoning; Ni/GDC anode
Remark doi:10.1016/j.ssi.2015.05.003
Link

High-temperature anion and proton conduction in RE3NbO7 (RE = La, Gd, Y, Yb, Lu) compounds

Authors A. Chesnauda, M.-D. Braidab, S. Estradd, F. Peird, A. Tarancnf, A. Morataf, G. Dezanneau
Source
Journal of the European Ceramic Society
Volume: 35, Issue: 11, Pages: 3051–3061
Time of Publication: 2015
Abstract The oxide-ion and proton conduction properties of RE3NbO7 (RE = La, Gd, Y, Yb, Lu) compounds were investigated. For the bigger rare-earth cation, i.e. La3+, the compound crystallises in a weberite-type structure and the oxide-ion conductivity is low owing to the lack of intrinsic oxygen vacancies. Consequently, the resultant proton incorporation and conductivity in La3NbO7 are also low. For small rare-earth cations, i.e. from Gd3+ to Lu3+ and for RE = Y, materials adopt a fluorite-like structure confirmed from X-ray powder diffraction. In this latter case, materials include intrinsic oxygen vacancies leading to a higher oxygen conductivity. For these compounds, a proton incorporation takes place at low temperature under wet conditions giving rise to proton conductivity. Nevertheless, both oxygen and proton conductivities are low in these materials, which can be explained by the ordering of oxygen vacancies observed by Transmission Electron Microscopy.
Keywords Protonic ceramic fuel cell; Rare-earth niobate; Combustion synthesis; Fluorite-type structure; Electrical properties
Remark doi:10.1016/j.jeurceramsoc.2015.04.014
Link

Proton transport properties of the RE3Ga5MO14 (RE = La, Nd and M = Si, Ti, Sn) langasite family of oxides

Authors Tor S. Bjrheim, Reidar Haugsrud
Source
Solid State Ionics
Volume: 275, Pages: 29–34
Time of Publication: 2015
Abstract Hydration and proton transport properties of novel, intrinsically acceptor doped compositions within the RE3Ga5MO14 family of oxides have been addressed by means of measurements of the electrical conductivity. Oxygen vacancies and protons charge compensate the acceptor in dry and wet atmospheres, respectively, and all compositions display significant proton conductivity below 1000 C. The hydration thermodynamics is affected by M-ion substitution, and becomes more favorable in the order Si < Ti < Sn. The enthalpy of proton mobility is also strongly dependent on the M-ion; M = Si, Ti and Sn exhibit enthalpies of proton mobility of 76 3, 61 1 and 80 2 kJ mol− 1, respectively.
Keywords Langasites; Conductivity; Defects; Acceptor; Hydration; Protons
Remark doi:10.1016/j.ssi.2015.03.014
Link

Diffusion of Nd and Mo in lanthanum tungsten oxide

Authors Einar Vllestad, Markus Teusner, Roger A. De Souza, Reidar Haugsrud
Source
Solid State Ionics
Volume: 274, Pages: 128–133
Time of Publication: 2015
Abstract Cation diffusion in functional oxides exposed to electrochemical gradients may lead to kinetic demixing or decomposition and, consequently, determine the life-time of the functional component. Here we present chemical diffusion coefficients of Nd and Mo in the mixed proton–electron conductor lanthanum tungsten oxide, La28 − xW4 + xO54 + 3x/2 (LWO), measured at 1000 to 1200 C in both oxidizing and reducing atmospheres. The bulk diffusivities of Nd and Mo were similar at all temperatures investigated and did not change significantly from oxidizing to reducing conditions. On these bases it is suggested that bulk diffusion of both Nd and Mo occurs via the La2 site on which both cations reside. Based on the low activation energy for bulk transport (~ 200 kJ∙mol− 1) at temperatures below 1200 C it is proposed that the cation defect concentrations are, in effect, frozen in. Preferential diffusion of Nd along the grain boundaries was rationalized based on space charge effects and depletion of W6 + and Mo6 + near the positively charged grain boundary core. Potential implications of kinetic demixing or decomposition of LWO membranes are also evaluated based on the present results.
Keywords Lanthanum tungstate; Cation diffusion; SIMS; Degradation; Tracer diffusion
Remark doi:10.1016/j.ssi.2015.03.011
Link

Crystal structure and high-temperature properties of the Ruddlesden–Popper phases Sr3−xYx(Fe1.25Ni0.75)O7−δ (0≤x≤0.75)

Authors Louise Samain, Philipp Amshoff, Jordi J. Biendicho, Frank Tietz, Abdelfattah Mahmoud, Raphal P. Hermann, Sergey Ya. Istomin, Jekabs Grins, Gunnar Svensson
Source
Journal of Solid State Chemistry
Volume: 227, Pages: 45–54
Time of Publication: 2015
Abstract Ruddlesden–Popper n=2 member phases Sr3−xYxFe1.25Ni0.75O7−δ, 0≤x≤0.75, have been investigated by X-ray and neutron powder diffraction, thermogravimetry and Mssbauer spectroscopy. Both samples as-prepared at 1300 C under N2(g) flow and samples subsequently air-annealed at 900 C were studied. The as-prepared x=0.75 phase is highly oxygen deficient with δ=1, the O1 atom site being vacant, and the Fe3+/Ni2+ ions having a square pyramidal coordination. For as-prepared phases with lower x values, the Mssbauer spectral data are in good agreement with the presence of both 5- and 4-coordinated Fe3+ ions, implying in addition a partial occupancy of the O3 atom sites that form the basal plane of the square pyramid. The air-annealed x=0.75 sample has a δ value of 0.61(1) and the structure has Fe/Ni ions in both square pyramids and octahedra. Mssbauer spectroscopy shows the phase to contain only Fe3+, implying that all Ni is present as Ni3+. Air-annealed phases with lower x values are found to contain both Fe3+ and Fe4+. For both the as-prepared and the air-annealed samples, the Y3+ cations are found to be mainly located in the perovskite block. The high-temperature thermal expansion of as-prepared and air-annealed x=0.75 phases were investigated by high-temperature X-ray diffraction and dilatometry and the linear thermal expansion coefficient determined to be 14.4 ppm K−1. Electrical conductivity measurements showed that the air-annealed samples have higher conductivity than the as-prepared ones.
Keywords Ruddlesden–Popper structure; Oxygen non-stoichiometry; Crystal structure; Mssbauer spectroscopy; Electrical conductivity; Thermal expansion
Remark doi:10.1016/j.jssc.2015.03.018
Link

Atmosphere dependence of anode reaction of intermediate temperature steam electrolysis using perovskite type proton conductor

Authors Takaaki Sakai, Keita Arakawa, Masako Ogushi, Tatsumi Ishihara, Hiroshige Matsumoto, Yuji Okuyama
Source
Journal of Solid State Electrochemistry
Volume: 19, Issue: 6, Pages: 1793-1798
Time of Publication: 2015
Abstract The effect of oxygen partial pressure on anode reaction of steam electrolysis using SrZr0.5Ce0.4Y0.1O3-α (SZCY-541) proton conducting electrolyte was investigated by AC impedance measurement in this work. The anode reaction was enhanced by increasing oxygen partial pressure, and this result was opposite to the expectation from the conventional anode reaction (water splitting reaction). The increase in the electrode reaction conductivity with oxygen chemical potential was proportional to PO21/4 at 600 C and at higher oxygen partial pressure region of 700 and 800 C, suggesting the possibility that the enhancement is caused by the increase in hole concentration on the electrolyte surface near the anode.
Remark Link

FD Electrolysis: Co-electrolysis of steam and CO2 in full-ceramic symmetrical SOECs: A strategy for avoiding the use of Hydrogen as a safe gas

Authors Marc Torrell, Sergio Garca-Rodrguez, Alex Morata, Germn Penelas and Alberto Tarancon
Source
Faraday Discussions
Time of Publication: 2015
Abstract The use of cermets as fuel electrodes for solid oxide electrolysis cells requires permanent circulation of reducing gas, e.g. H2 or CO, so called safe gas, in order to avoid oxidation of the metallic phase. Replacing metallic based electrodes by pure oxides is therefore proposed as an advantage for the industrial application of solid oxide electrolyzers. In this work, full-ceramic symmetrical solid oxide electrolysis cells have been investigated for steam/CO2 co-electrolysis. Electrolyte supported cells with La0.75Sr0.25Cr0.5Mn0.5O3-δ reversible electrodes have been fabricated and tested in co-electrolysis mode using different fuel compositions, from pure H2O to pure CO2, at temperatures of 850C – 900C. Electrochemical impedance spectroscopy and galvanostatic measurements have been carried out for the mechanistic understanding of the symmetrical cells performance. The content of H2 and CO in the product gas has been measured by in-line gas micro-chromatography. The effect of employing H2 as a safe gas has been also investigated. Maximum density currents of 750 mA/cm2 and 620 mA/cm2 have been applied at 1.7 V for pure H2O and for H2O:CO2 ratios of 1:1, respectively. Remarkable results were obtained for hydrogen-free fuel compositions, which confirmed the interest of using ceramic oxides as a fuel electrode candidate to reduce or completely avoid the use of safe gas in operation minimizing the contribution of the reverse water shift reaction (RWSR) in the process. H2:CO ratios close to two were obtained for hydrogen-free tests fulfilling the basic requirements for synthetic fuel production. An important increase of the operation voltage was detected under continuous operation leading to a dramatic failure by delamination of the oxygen electrode.
Remark Accepted Manuscript, DOI: 10.1039/C5FD00018A
Link

Doping strategies for increased oxygen permeability of CaTiO3 based membranes

Authors Jonathan M. Polfus, Wen Xing, Martin F. Sunding, Sidsel M. Hanetho, Paul Inge Dahl, Yngve Larring, Marie-Laure Fontaine, Rune Bredesen
Source
Journal of Membrane Science
Volume: 482, Pages: 137–143
Time of Publication: 2015
Abstract Oxygen permeation measurements are performed on dense samples of CaTi0.85Fe0.15O3−δ, CaTi0.75Fe0.15Mg0.05O3−δ and CaTi0.75Fe0.15Mn0.10O3−δ in combination with density functional theory (DFT) calculations and X-ray photoelectron spectroscopy (XPS) in order to assess Mg and Mn as dopants for improving the O2 permeability of CaTi1−xFexO3−δ based oxygen separation membranes. The oxygen permeation measurements were carried out at temperatures ranging between 700 and 1000 C with feed side oxygen partial pressures between 0.01 and 1 bar. The O2 permeability was experimentally found to be highest for the Mn doped sample over the whole temperature range, reaching 4.210−3 ml min−1 cm−1 at 900 C and 0.21 bar O2 in the feed which corresponds to a 40% increase over the Fe-doped sample and similar to reported values for x=0.2. While the O2 permeability of the Mg doped sample was also higher than the Fe-doped sample, it approached that of the Fe-doped sample above 900 C. According to the DFT calculations, Mn introduces electronic states within the band gap and will predominately exist in the effectively negative charge state, as indicated by XPS measurements. Mn may therefore improve the ionic and electronic conductivity of CTF based membranes. The results are discussed in terms of the limiting species for ambipolar transport and O2 permeability, i.e., oxygen vacancies and electronic charge carriers.
Keywords Dense ceramic oxygen membrane; Ambipolar transport; Mixed ionic-electronic conduction; CaTiO3; Calcium titanate
Remark doi:10.1016/j.memsci.2015.02.036
Link

Coated stainless steel 441 as interconnect material for solid oxide fuel cells: Evolution of electrical properties

Authors Jan Gustav Grolig , Jan Froitzheim, Jan-Erik Svensson
Source
Journal of Power Sources
Volume: 284, Pages: 321–327
Time of Publication: 2015
Abstract AISI 441 coated with a double layer coating of 10 nm cerium (inner layer) and 630 nm cobalt was investigated and in addition the uncoated material was exposed for comparison. The main purpose of this investigation was the development of a suitable ASR characterization method. The material was exposed to a simulated cathode atmosphere of air with 3% water at 850 C and the samples were exposed for up to 1500 h. We compared two methods of ASR measurements, an in-situ method where samples were measured with platinum electrodes for longer exposure times and an ex-situ method where pre-oxidized samples were measured for only very short measurement times. It was found that the ASR of ex-situ characterized samples could be linked to the mass gain and the electrical properties could be linked to the evolving microstructure during the different stages of exposure. Both the degradation of the electric performance and the oxygen uptake (mass gain) followed similar trends. After about 1500 h of exposure an ASR value of about 15 mΩcm2 was reached. The in-situ measured samples suffered from severe corrosion attack during measurement. After only 500 h of exposure already a value of 35 mΩcm2 was obtained.
Keywords ASR; Interconnect; AISI 441; SOFC; Corrosion; Platinum
Remark doi:10.1016/j.jpowsour.2015.03.029
Link

Steam-promoted CO2 flux in dual-phase CO2 separation membranes

Authors Wen Xing, Thijs Peters, Marie-Laure Fontaine, Anna Evans, Partow Pakdel Henriksen, Truls Norby, Rune Bredesen
Source
Journal of Membrane Science
Volume: 482, Pages: 115–119
Time of Publication: 2015
Abstract Steam dissolving into molten carbonates through the formation of hydroxide ions could contribute to the permeation of CO2 in dual-phase membranes under certain conditions. In this work, ceria (CeO2) supported dual-phase membranes was fabricated and the effect of steam on the transport properties has been investigated by means of flux measurements. The results show an approximate 30% increase of the CO2 flux when 2.5% steam is introduced to the feed side, while an approximate 250–300% increase of the CO2 flux is observed when introducing the same amount of steam to the sweep side. These phenomena and transport mechanisms are explained by the theory of ambipolar permeation of CO2 via various combinations of charged species.
Keywords Dual-phase; CO2 separation membrane; Steam; Flux
Remark doi:10.1016/j.memsci.2015.02.029
Link

Electrical conductivity and thermopower of (1 − x) BiFeO3 – xBi0.5K0.5TiO3 (x = 0.1, 0.2) ceramics near the ferroelectric to paraelectric phase transition

Authors E. T. Wefring, M.-A. Einarsrud and T. Grande
Source
Physical Chemistry Chemical Physics
Volume: 17, Issue: 14, Pages: 9420-9428
Time of Publication: 2015
Abstract Ferroelectric BiFeO3 has attractive properties such as high strain and polarization, but a wide range of applications of bulk BiFeO3 are hindered due to high leakage currents and a high coercive electric field. Here, we report on the thermal behaviour of the electrical conductivity and thermopower of BiFeO3 substituted with 10 and 20 mol% Bi0.5K0.5TiO3. A change from p-type to n-type conductivity in these semi-conducting materials was demonstrated by the change in the sign of the Seebeck coefficient and the change in the slope of the isothermal conductivity versus partial pressure of O. A minimum in the isothermal conductivity was observed at [similar]10−2 bar O2 partial pressure for both solid solutions. The strong dependence of the conductivity on the partial pressure of O2 was rationalized by a point defect model describing qualitatively the conductivity involving oxidation/reduction of Fe3+, the dominating oxidation state of Fe in stoichiometric BiFeO3. The ferroelectric to paraelectric phase transition of 80 and 90 mol% BiFeO3 was observed at 648 15 and 723 15 C respectively by differential thermal analysis and confirmed by dielectric spectroscopy and high temperature powder X-ray diffraction.
Remark DOI: 10.1039/C5CP00266D
Link

Structure and conductivity of acceptor doped La2BaZnO5 and Nd2BaZnO5

Authors Md. Khairul Hoque, Reidar Haugsrud, Christopher S. Knee
Source
Solid State Ionics
Volume: 272, Pages: 160–165
Time of Publication: 2015
Abstract The effect of calcium substitution on the structure and electrical conductivity of Ln2 − xCaxBaZnO5 − δ, Ln = La and Nd, has been studied. Differing trends with respect to dependence of the unit cell volume were observed as a function of Ca substitution. For both series of materials the limit of Ca substitution was estimated to be x ≈ 0.2. The electrical conductivity was studied in the temperature range of 1000–350 C using electrochemical impedance spectroscopy in argon and oxygen atmospheres and via isotherms between 400 and 1000 C as function of oxygen pressure and the water vapour pressure. A marked increase in conductivity of approx. two orders of magnitude was explained by the presence of oxygen vacancies in the calcium doped samples. At pO2 < 10− 12 atm the x = 0.15 materials are predominantly oxygen ion conductors, and La1.85Ca0.15BaZnO5 − δ displays a peak conductivity of 0.002 S cm− 1 at 1000 C. The materials display a rise in conductivity in oxidizing conditions, indicating a significant p-type contribution.
Keywords Oxide ion conductor; Mixed conductor; Synthesis; Impedance spectroscopy; SOFC
Remark doi:10.1016/j.ssi.2015.02.001
Link

Dual atmosphere study of the K41X stainless steel for interconnect application in high temperature water vapour electrolysis

Authors M.R. Ardigo, I. Popa, L. Combemale, S. Chevalier, F. Herbst, P. Girardon
Source
International Journal of Hydrogen Energy
Volume: 40, Issue: 15, Pages: 5305–5312
Time of Publication: 2015
Abstract High temperature water vapour electrolysis (HTE) is one of the most efficient technologies for mass hydrogen production. A major technical difficulty related to high temperature water vapour electrolysis is the development of interconnects working efficiently for a long period. Working temperature of 800 C enables the use of metallic materials as interconnects. High temperature corrosion behaviour and electrical conductivity of a commercial stainless steel, K41X (AISI 441), were tested in HTE dual atmosphere (95%O2-5%H20/10%H2-90%H2O) at 800 C. The alloy exhibits a very good oxidation resistance compared to single atmosphere tests. However, a supplied electrical current significantly changes the nature of the oxides that form during the test. A very good Area Specific Resistance (ASR) parameter was measured in dual atmosphere, much lower than the values obtained in single atmosphere tests.
Remark doi:10.1016/j.ijhydene.2015.01.116
Link

Solid oxide fuel cells with (La,Sr)(Ga,Mg)O3-δ electrolyte film deposited by radio-frequency magnetron sputtering

Authors Sea-Fue Wang, His-Chuan Lu, Yung-Fu Hsu, Yi-Xuan Hu
Source
Journal of Power Sources
Volume: 281, Pages: 258–264
Time of Publication: 2015
Abstract In this study, solid oxide fuel cells (SOFCs) containing a high quality La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) film deposited on anode supported substrate using RF magnetron sputtering are successfully prepared. The anode substrate is composed of two functional NiO/Sm0.2Ce0.8O2-δ (SDC) composite layers with ratios of 60/40 wt% and 50/50 wt% and a current collector layer of pure NiO. The as-deposited LSGM film appears to be amorphous in nature. After post-annealing at 1000 C, a uniform and dense polycrystalline film with a composition of La0.87Sr0.13Ga0.85Mg0.15O3-δ and a thickness of 3.8 μm is obtained, which was well adhered to the anode substrate. A composite LSGM/La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) layer, with a ratio of 30/70 wt%, is used as the cathode. The SOFC prepared reveals a good mechanical integrity with no sign of cracking, delamination, or discontinuity among the interfaces. The total cell resistance of a single cell with LSGM electrolyte film declines from 0.60 to 0.10 Ω cm2 as the temperature escalates from 600 to 800 C and the open circuit voltage (OCV) ranges from 0.85 to 0.95 V. The maximum power density (MPD) of the single cell is reported as 0.65, 1.02, 1.30, 1.42, and 1.38 W cm−2 at 600, 650, 700, 750, and 800 C, respectively. The good cell performance leads to the conclusion that RF magnetron sputtering is a feasible deposition method for preparing good quality LSGM films in SOFCs.
Keywords Solid oxide fuel cell; Sputtering; Electrolyte; Doped lanthanum gallate
Remark doi:10.1016/j.jpowsour.2015.01.185
Link

Phase equilibria in the Cs2MoO4–ZnMoO4–Zr(MoO4)2 system, Crystal structures and properties of new triple molybdates Cs2ZnZr(MoO4)4 and Cs2ZnZr2(MoO4)6

Authors Galina D. Tsyrenova, Sergey F. Solodovnikov, Nadezhda N. Popova, Zoya A. Solodovnikova, Erzhena T. Pavlova, Dmitry Yu. Naumov, Bogdan I. Lazoryak
Source
Volume: 81, Pages: 93–99
Time of Publication: 2015
Abstract Subsolidus phase relations in the Cs2MoO4–ZnMoO4–Zr(MoO4)2 system were determined and two new compounds, Cs2ZnZr(MoO4)4 and Cs2ZnZr2(MoO4)6, were obtained. The structure of Cs2ZnZr(MoO4)4 (a=5.7919(1) , c=8.0490(3) ; space group P View the MathML source3m1; Z=0.5; R=0.0149) belongs to the layered glaserite-like KAl(MoO4)2 structure type where the octahedral Al3+ positions are statistically occupied by 0.5 Zn2++0.5 Zr4+. The second triple molybdate, Cs2ZnZr2(MoO4)6 (a=13.366(1) , c=12.253(3) , space group R View the MathML source3, Z=3, R=0.0324), is isostructural to Cs2MnZr2(MoO4)6 and Cs2M2Zr(MoO4)6 (M=Al, Fe) and contains a mixed 3D framework built of МоO4 tetrahedra and (Zn, Zr)O6 octahedra sharing common vertices. Cesium cations are located in large channels of the framework. The latter compound undergoes a first-order phase transition at 723 K with considerable increasing its ionic conductivity.
Keywords Cesium; Zinc; Zirconium; Triple molybdates; Crystal structure; X-ray diffraction; IR and Raman spectra; Conductivity
Remark doi:10.1016/j.jpcs.2015.01.015
Link

Binder Jetting: A Novel Solid Oxide Fuel-Cell Fabrication Process and Evaluation

Authors Guha Manogharan, Meshack Kioko, Clovis Linkous
Source
JOM
Volume: 67, Issue: 3, Pages: 660-667
Time of Publication: 2015
Abstract With an ever-growing concern to find a more efficient and less polluting means of producing electricity, fuel cells have constantly been of great interest. Fuel cells electrochemically convert chemical energy directly into electricity and heat without resorting to combustion/mechanical cycling. This article studies the solid oxide fuel cell (SOFC), which is a high-temperature (100C to 1000C) ceramic cell made from all solid-state components and can operate under a wide range of fuel sources such as hydrogen, methanol, gasoline, diesel, and gasified coal. Traditionally, SOFCs are fabricated using processes such as tape casting, calendaring, extrusion, and warm pressing for substrate support, followed by screen printing, slurry coating, spray techniques, vapor deposition, and sputter techniques, which have limited control in substrate microstructure. In this article, the feasibility of engineering the porosity and configuration of an SOFC via an additive manufacturing (AM) method known as binder jet printing was explored. The anode, cathode and oxygen ion-conducting electrolyte layers were fabricated through AM sequentially as a complete fuel cell unit. The cell performance was measured in two modes: (I) as an electrolytic oxygen pump and (II) as a galvanic electricity generator using hydrogen gas as the fuel. An analysis on influence of porosity was performed through SEM studies and permeability testing. An additional study on fuel cell material composition was conducted to verify the effects of binder jetting through SEM–EDS. Electrical discharge of the AM fabricated SOFC and nonlinearity of permeability tests show that, with additional work, the porosity of the cell can be modified for optimal performance at operating flow and temperature conditions.
Remark DOI 10.1007/s11837-015-1296-9
Link

Hydrogen separation membranes based on dense ceramic composites in the La27W5O55.5–LaCrO3 system

Authors Jonathan M. Polfus, Wen Xing, Marie-Laure Fontaine, Christelle Denonville, Partow P. Henriksen, Rune Bredesen
Source
Journal of Membrane Science
Volume: 479, Pages: 39–45
Time of Publication: 2015
Abstract Some compositions of ceramic hydrogen permeable membranes are promising for integration in high temperature processes such as steam methane reforming due to their high chemical stability in large chemical gradients and CO2 containing atmospheres. In the present work, we investigate the hydrogen permeability of densely sintered ceramic composites (cercer) of two mixed ionic-electronic conductors: La27W3.5Mo1.5O55.5−δ (LWM) containing 30, 40 and 50 wt% La0.87Sr0.13CrO3−δ (LSC). Hydrogen permeation was characterized as a function of temperature, feed side hydrogen partial pressure (0.1–0.9 bar) with wet and dry sweep gas. In order to assess potentially limiting surface kinetics, measurements were also carried out after applying a catalytic Pt-coating to the feed and sweep side surfaces. The apparent hydrogen permeability, with contribution from both H2 permeation and water splitting on the sweep side, was highest for LWM70-LSC30 with both wet and dry sweep gas. The Pt-coating further enhances the apparent H2 permeability, particularly at lower temperatures. The apparent H2 permeability at 700 C in wet 50% H2 was 1.110−3 mL min−1 cm−1 with wet sweep gas, which is higher than for the pure LWM material. The present work demonstrates that designing dual-phase ceramic composites of mixed ionic-electronic conductors is a promising strategy for enhancing the ambipolar conductivity and gas permeability of dense ceramic membranes.
Keywords Hydrogen separation; Dense ceramic membrane; Ceramic–ceramic composite; Lanthanum tungstate; Lanthanum chromite
Remark doi:10.1016/j.memsci.2015.01.027
Link

Bi1−xNbxO1.5+x (x=0.0625, 0.12) fast ion conductors: Structures, stability and oxide ion migration pathways

Authors Matthew L. Tate, Jennifer Hack, Xiaojun Kuang, Garry J. McIntyre, Ray L. Withers, Mark R. Johnson, Ivana Radosavljevic Evans
Source
Journal of Solid State Chemistry
Volume: 225, Pages: 383–390
Time of Publication: 2015
Abstract A combined experimental and computational study of Bi1−xNbxO1.5+x (x=0.0625 and 0.12) has been carried out using laboratory X-ray, neutron and electron diffraction, impedance measurements and ab-initio molecular dynamics. We demonstrate that Bi0.9375Nb0.0625O1.5625, previously reported to adopt a cubic fluorite-type superstructure, can form two different polymorphs depending on the synthetic method: a metastable cubic phase is produced by quenching; while slower cooling yields a stable material with a tetragonal √2√21 superstructure, which undergoes a reversible phase transition into the cubic form at ~680 C on subsequent reheating. Neutron diffraction reveals that the tetragonal superstructure arises mainly from ordering in the oxygen sublattice, with Bi and Nb remaining disordered, although structured diffuse scattering observed in the electron diffraction patterns suggests a degree of short-range ordering. Both materials are oxide ion conductors. On thermal cycling, Bi0.88Nb0.12O1.62 exhibits a decrease in conductivity of approximately an order of magnitude due to partial transformation into the tetragonal phase, but still exhibits conductivity comparable to yttria-stabilised zirconia (YSZ). Ab-initio molecular dynamics simulations performed on Bi0.9375Nb0.0625O1.5625 show that oxide ion diffusion occurs by O2− jumps between edge- and corner-sharing OM4 groups (M=Bi, Nb) via tetrahedral □M4 and octahedral □M6 vacancies.
Keywords Functional oxides; Fast ion conductors; Complex superstructures
Remark doi:10.1016/j.jssc.2015.01.006
Link

Functional properties of La0.99X0.01Nb0.99Al0.01O4−δ and La0.99X0.01Nb0.99Ti0.01O4−δ proton conductors where X is an alkaline earth cation

Authors Mariya E. Ivanova, Wilhelm A. Meulenberg, Justinas Palisaitis, Doris Sebold, Cecilia Sols, Mirko Ziegner, Jose M. Serra, Joachim Mayer, Michael Hnsel, Olivier Guillon
Source
Journal of the European Ceramic Society
Volume: 35, Issue: 4, Pages: 1239–1253
Time of Publication: 2015
Abstract Lanthanum niobates with general formulas of La0.99X0.01Nb0.99Al0.01O4−δ and La0.99X0.01Nb0.99Ti0.01O4−δ (X = Mg, Ca, Sr or Ba) were synthesized via the conventional solid state reaction. Specimens with relative density above 96% were produced after sintering. Structural and phase composition studies revealed predominant monoclinic Fergusonite structure for the majority of samples. SEM and TEM studies elucidated the effect of the used dopant combinations on grain growth, micro-crack formation and secondary phase formation. Results from microstructural study were correlated to the grain interior and grain boundary conductivities for selected samples (La0.99Sr0.01Nb0.99Al0.01O4−δ and La0.99Sr0.01Nb0.99Ti0.01O4−δ). The majority of co-doped niobates exhibited appreciable protonic conductivity under humid atmospheres at intermediate temperatures. Sr- or Ca-doped compounds displayed the highest total conductivities with values for LSNA equal to 6 10−4 S/cm and 3 10−4 S/cm in wet air and in wet 4% H2–Ar (900 C), respectively. Additionally, thermal expansion was studied to complete functional characterization of co-doped LaNbO4.
Keywords Proton-conducting ceramic materials; Hydrogen transport ceramic membranes; Rare earth ortho-niobates; Acceptor-doped lanthanum niobates
Remark doi:10.1016/j.jeurceramsoc.2014.11.009
Link

Hydrogen permeation, water splitting and hydration kinetics in Nd5.4Mo0.3W0.7O12−δ

Authors Zuoan Li, Christian Kjlseth, Reidar Haugsrud
Source
Journal of Membrane Science
Volume: 476, Pages: 105–111
Time of Publication: 2015
Abstract To investigate transport properties of Mo-substituted Nd5.4Mo0.3W0.7O12−δ for hydrogen separation application, hydrogen fluxes of Nd5.4Mo0.3W0.7O12−δ have been measured in both dry and wet sweep gases. The fluxes in dry sweep gas show lower temperature dependence at high temperatures than at low temperatures. Comparing the hydrogen permeability among rare earth tungstates, it has been revealed that the larger the RE-site cation radius, the higher the hydrogen permeation. Water splitting effect for the wet sweep gas has been confirmed by mass spectrometry. Oxygen surface kinetics under oxidizing conditions has been studied by ToF-SIMS measurements, and is significantly faster under wet conditions than dry. Hydration kinetics has been studied by conductivity relaxation measurements under reducing conditions for the first time, showing a two-fold non-monotonic behavior.
Keywords Hydrogen permeation; Hydration kinetics; Water splitting; Oxygen surface kinetics; Nd5.4Mo0.3W0.7O12−δ
Remark doi:10.1016/j.memsci.2014.11.013
Link

Savitha Thayumanasundaram, Vijay Shankar Rangasamy, Niels De Greef, Jin Won Seo andJean-Pierre Locquet

Author Hybrid Polymer Electrolytes Based on a Poly(vinyl alcohol)/Poly(acrylic acid) Blend and a Pyrrolidinium-Based Ionic Liquid for Lithium-Ion Batteries
Source
European Journal of Inorganic Chemistry
Volume: 2015, Issue: 7, Pages: 1290–1299
Time of Publication: 2014
Abstract Polymer blends of poly(vinyl alcohol) (PVA) and poly(acrylic acid) (PAA) were prepared with different molar ratios by a solvent-casting technique. The XRD patterns of the blends show that the degree of crystallinity of the PVA membranes decreases with the addition of PAA owing to the formation of interpenetrating polymer chains. The vibrational spectra of the blend membranes reveal the formation of strong hydrogen bonding between PVA and PAA. Dynamic mechanical analysis (DMA) reveals that the storage modulus of a 25 mol-% PAA sample is comparable to that of pure PVA and, therefore, confirms the mechanical stability of the blend membranes. Significant changes in the peak areas and chemical shifts of the PVA hydroxyl signal (δ = 4–5 ppm) in the 1H NMR spectra of the blend membranes confirm the strong hydrogen bonding between the OH groups of PVA and PAA. The ionic liquid (IL) 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI) with 0.2 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was added to the polymer blend to prepare flexible, nonvolatile hybrid polymer electrolytes for lithium-ion batteries. A maximum ionic conductivity of 1 mS cm–1 is observed at 90 C for the membrane with 70 mol-% IL.
Keywords Polymers;Ionic liquids;Hybrid membranes;Hydrogen bonds;Lithium batteries
Remark DOI: 10.1002/ejic.201402603
Link

Pure and Mn-doped La4SrTi5O17 layered perovskite as potential solid oxide fuel cell material: Structure and anodic performance

Authors Cdric Prillat-Merceroz, Pascal Roussel, Marielle Huv, Edouard Capoen, Sbastien Rosini, Patrick Glin, Rose-Nolle Vannier, Gilles H. Gauthier
Source
Journal of Power Sources
Volume: 274, Pages: 806–815
Time of Publication: 2015
Abstract Pure and 5% Mn doped layered perovskites La4SrTi5O17, members of the La4Srn-4(Ti,Mn)nO3n+2 series with n = 5, have been synthesized and investigated as anode materials for Solid Oxide Fuel Cells. The use of XRD, neutron and electron diffraction techniques allows clarifying some divergences concerning the structural characterization within the family, not only in air but also in anodic-like N2/H2(97/3) atmosphere. The electrical conductivity of both compounds is very low in air but those values increase by two orders of magnitude in diluted hydrogen. The study of catalytic properties for methane steam reforming as well as in-depth analysis of the SOFC anodic behaviour of both materials are described, for which a microstructure optimization of the electrode allows to demonstrate the potential interest of the lamellar materials upon the classical three-dimensional cubic-like LSTs.
Keywords SOFC; Anode; Layered perovskite; Titanate; Methane steam reforming; Electrochemical impedance spectroscopy
Remark doi:10.1016/j.jpowsour.2014.10.131
Link

Electrochemical performance and carbon deposition resistance of Ce-doped La0.7Sr0.3Fe0.5Cr0.5O3-δ anode materials for solid oxide fuel cells fed with syngas

Authors Yi-Fei Sun, Jian-Hui Li, Kart T. Chuang, Jing-Li Luo
Source
Journal of Power Sources
Volume: 254, Pages: 483–487
Time of Publication: 2015
Abstract Ce-doped La0.7Sr0.3Fe0.5Cr0.5O3-δ (Ce-LSFC) perovskite anode catalysts for solid oxide fuel cells are successfully synthesized by a modified combustion method for the first time. The pure perovskite structure without formation of CeO2 is obtained when the content of Ce ≤ 10%. Compared with La0.7Sr0.3Fe0.5Cr0.5O3-δ anode, Ce-LSFC anode not only shows much higher catalytic activity towards the oxidation of syngas with less carbon deposition, but also displays better regeneration from coking. The enhanced performance is attributed to the more available oxygen vacancies in lattice and better oxygen mobility after doping with Ce.
Keywords SOFC; Ce-doped LSFC; Perovskite
Remark doi:10.1016/j.jpowsour.2014.10.090
Link

Visualization of conduction pathways in a lanthanum lithium titanate superionic conductor synthesized by rapid cooling

Authors Kazuhiro Mori, Shogo Tomihira, Kenji Iwase, Toshiharu Fukunaga
Source
Solid State Ionics
Volume: 268, Issue: A, Pages: 76-81
Time of Publication: 2014
Abstract Three-dimensional structure and conduction pathways of the lithium ions in 7Li0.4La0.53TiO3 quenched with liquid nitrogen were studied using reverse Monte Carlo modeling and the bond valence sum approach using neutron diffraction data. The lithium ions were primarily located in the region between the off-center positions of the A-sites and bottlenecks defined by four coordinating oxygen ions. The bottlenecks in the predicted conduction pathways of the lithium ions were classified into three types (I, II, and III) by their size. The type II bottlenecks were the most accessible to lithium-ion migration and more than 70% of the bottlenecks were type II.
Keywords Lithium-ion conductor; Lanthanum lithium titanate; Local structure; Neutron diffraction; Reverse Monte Carlo modeling; Bond valence sum
Remark doi:10.1016/j.ssi.2014.09.030
Link

Functional properties of La0.99X0.01Nb0.99Al0.01O4−δ and La0.99X0.01Nb0.99Ti0.01O4−δ proton conductors where X is an alkaline earth cation

Authors Mariya E. Ivanovaa, Wilhelm A. Meulenberga, Justinas Palisaitisb, Doris Sebolda, Cecilia Solsd, Mirko Ziegnere, Jose M. Serrad, Joachim Mayerb, Michael Hnsele, Olivier Guillona
Source
Journal of the European Ceramic Society
Time of Publication: 2014-12
Abstract Lanthanum niobates with general formulas of La0.99X0.01Nb0.99Al0.01O4−δ and La0.99X0.01Nb0.99Ti0.01O4−δ (X = Mg, Ca, Sr or Ba) were synthesized via the conventional solid state reaction. Specimens with relative density above 96% were produced after sintering. Structural and phase composition studies revealed predominant monoclinic Fergusonite structure for the majority of samples. SEM and TEM studies elucidated the effect of the used dopant combinations on grain growth, micro-crack formation and secondary phase formation. Results from microstructural study were correlated to the grain interior and grain boundary conductivities for selected samples (La0.99Sr0.01Nb0.99Al0.01O4−δ and La0.99Sr0.01Nb0.99Ti0.01O4−δ). The majority of co-doped niobates exhibited appreciable protonic conductivity under humid atmospheres at intermediate temperatures. Sr- or Ca-doped compounds displayed the highest total conductivities with values for LSNA equal to 6 10−4 S/cm and 3 10−4 S/cm in wet air and in wet 4% H2–Ar (900 C), respectively. Additionally, thermal expansion was studied to complete functional characterization of co-doped LaNbO4.
Keywords Proton-conducting ceramic materials, Hydrogen transport ceramic membranes, Rare earth ortho-niobates, Acceptor-doped lanthanum niobates, ProGasMix
Remark Link

Versatile apparatus for thermoelectric characterization of oxides at high temperatures

Authors Matthias Schrade, Harald Fjeld, Truls Norby and Terje G. Finstad
Source
Review of Scientific Instruments
Volume: 85, Pages: 103906
Time of Publication: 2014
Abstract An apparatus for measuring the Seebeck coefficient and electrical conductivity is presented and characterized. The device can be used in a wide temperature range from room temperature to 1050 C and in all common atmospheres, including oxidizing, reducing, humid, and inert. The apparatus is suitable for samples with different geometries (disk-, bar-shaped), allowing a complete thermoelectric characterization (including thermal conductivity) on a single sample. The Seebeck coefficient α can be measured in both sample directions (in-plane and cross-plane) simultaneously. Electrical conductivity is measured via the van der Pauw method. Perovskite-type CaMnO3 and the misfit cobalt oxide (Ca2CoO3) q (CoO2) are studied to demonstrate the temperature range and to investigate the variation of the electrical properties as a function of the measurement atmosphere.
Remark http://dx.doi.org/10.1063/1.4897489
Link

Electrochemical behavior of the pyrochlore- and fluorite-like solid solutions in the Pr2O3–ZrO2 system. Part I

Authors D.A. Belov, A.V. Shlyakhtina, J.C.C. Abrantes, S.A. Chernyak, G.A. Gasymova, O.K. Karyagina, L.G. Shcherbakova
Source
Solid State Ionics
Time of Publication: 2014
Abstract We have studied the structure, microstructure, and electrochemical properties in air of (Pr2 − xZrx)Zr2O7 + x/2 (x = 0.15, 0.32, 0.78), Pr2Zr2O7, and Pr2(Zr2 − xPrx)O7 − x/2 (x = 0.1, 0.4, 1) materials. The solid solutions were prepared through coprecipitation followed by heat treatment of the precursors at 1550 C for 4 h. According to XRD data, the extent of the pyrochlore-like Pr2 xZr2 xO7 x/2 solid solutions at 1550 C is ~ 6 mol.%, which is considerably smaller than that in the NdZrO and SmZrO systems at this temperature. Among the pyrochlores, the highest bulk conductivity was offered by the (Pr2 − xZrx)Zr2O7 + x/2 (x = 0.15): 7.15 10− 3 S/cm at 800 C (Ea = 0.66 eV). The pyrochlore-like Pr2(Zr2 − xPrx)O7 − x/2 (x = 0.1) had lower conductivity (3.97 10− 3 S/cm at 800 C). The highest bulk conductivity among the materials studied was found in the Pr2O3-rich fluorite-like Pr2(Zr2 − xPrx)O7 − x/2 with x = 1: ~ 0.217 S/cm at 800 C (Ea = 0.0.31 eV). The temperature-dependent conductivity of the Pr2O3-rich fluorite-like solid solutions Pr2(Zr2 − xPrx)O7 − x/2 with x = 0.4 and 1 had a break at 560 C, suggesting a change in the mechanism of ion transport at this temperature.
Remark DOI: 10.1016/j.ssi.2014.09.035
Link

Thermal Depolarization in the High-Temperature Ternary Piezoelectric System xPbTiO3–yBiScO3–zBi(Ni1/2Ti1/2)O3

Authors Troy Y. Ansell, David P. Cann, Eva Sapper and Jrgen Rdel
Source
Journal of the American Ceramic Society
Time of Publication: 2014
Abstract In the high-temperature ternary perovskite piezoelectric system xPbTiO3–yBiScO3–zBi(Ni1/2,Ti1/2)O3 (PT–BS–BNiT), the addition of bismuth to the A site and nickel to the B site leads to compositions that exhibit diffuse relaxor-like behavior. For these, depolarization temperature, not Curie point, is the critical value of temperature. Depolarization temperature (Td) is defined as the temperature at which the steepest loss in polarization occurs. This temperature is observed in poled materials through two different methods: loss tangent measurements and in situ d33. Across the ternary system, multiple dielectric anomalies occurred which was observed in dielectric tests where the dielectric peak broadens and becomes frequency dependent as BNiT content increased. For different compositions, the value of Td ranged between 275C–375C. Values for the piezoelectric coefficient increased with temperature up to d33 = 1000 pC/N during in situ d33. High temperature (up to 190C) and high field (up to 40 kV/cm) were also applied to test ferroelectric properties in these regimes.
Remark DOI: 10.1111/jace.13268
Link

Characterization and Modeling of La 1 − x Sr x CoO 3 − δ Solid Oxide Fuel Cell Cathodes Using Nonlinear Electrochemical Impedance Techniques

Author Timothy James McDonald
Source
Time of Publication: 2014
Remark Dissertation
Link

Structural and electrical study of samarium doped cerium oxide thin films prepared by e-beam evaporation

Authors Darius Virbukas, Mantas Sriubas, Giedrius Laukaitis
Source
Solid State Ionics
Time of Publication: 2014
Abstract Samarium doped cerium oxide (Sm0.15Ce0.85O1.925, SDC) thin films were grown on the Alloy 600 (Fe–Ni–Cr) and optical quartz (SiO2) substrates using e-beam deposition technique. Formed SDC thin films were characterized using different X-ray diffraction (XRD) techniques, scanning electron microscope (SEM), energy-dispersive spectrometry (EDS) and impedance spectroscopy. The deposition rate of formed SDC thin films was changed from 2 /s to 16 /s. XRD analysis shows that all thin films have a cubic (FCC) structure and repeat the crystallographic orientation of the initial powders evaporated with different deposition rate and on different substrates. The crystallite size increases from 7.7 nm to 10.3 nm and from 7.2 nm to 9.2 nm on Alloy 600 substrate and optical quartz (SiO2) substrate respectively as the thin film deposition rate increases. SEM images indicate a dense and homogeneous structure of all formed SDC thin films. The ionic conductivity depends on thin films density and blocking factor. The best ionic conductivity (σg = 1.34 Sm− 1 and σgb = 2.29 Sm −1 at 873 K temperature, activation energy ΔEg = 0.91 eV and ΔEgb = 0.99 eV) was achieved for SDC thin films formed at 4 /s deposition rate. It was found that the highest density (5.25 g/cm3) and the lowest relaxation time in grain (τg = 9.83 10− 7 s), and the lowest blocking factor (0.39) is in SDC thin films formed at 4 /s deposition rate. The deposition rate influences the stoichiometry of the formed SDC thin ceramic films.
Keywords Electron beam deposition; Samarium doped ceria oxide (SDC); Solid oxide fuel cells (SOFC); Ionic conductivity
Remark DOI: 10.1016/j.ssi.2014.09.036
Link

Electrical conductivity and TG-DSC study of hydration of Sc-doped CaSnO3 and CaZrO3

Authors Andreas Lken, Christian Kjlseth, Reidar Haugsrud
Source
Solid State Ionics
Volume: 267, Pages: 61–67
Time of Publication: 2014
Abstract Correlations linking hydration thermodynamics to materials parameters can be of vital importance for further development of proton conducting oxides. However, the currently proposed correlations are troubled by scattering limiting their predictive power. As such, the present contribution has investigated Sc-doped CaSnO3 and CaZrO3 in an attempt to further elucidate the trends in the thermodynamics of hydration for perovskites. Conductivity and impedance spectroscopy on 5 and 10% Sc-doped CaSnO3 demonstrated that it is primarily an oxygen ion conductor with a small protonic contribution at lower temperatures (below 500 C) under wet conditions. Simultaneous thermogravimetry (TG) and differential scanning calorimetry (DSC), TG-DSC, was applied to measure the standard molar hydration enthalpy of CaSn1−xScxO3−δ and CaZr1−xScxO3−δ (x = 0.05, 0.10, 0.15 and 0.20) as a function of the Sc concentration. The hydration enthalpy becomes increasingly negative with increasing Sc substitution, which is discussed on the basis of changes in electronegativity, basicity and tolerance factor.
Keywords Defects; Protons; Hydration; Thermodynamics; Perovskites
Remark DOI: 10.1016/j.ssi.2014.09.006
Link

Synthesis, crystal structure and properties of alluaudite-like triple molybdate Na25Cs8Fe5(MoO4)24

Authors Aleksandra A. Savina, Sergey F. Solodovnikov, Dmitry A. Belov, Olga M. Basovich, Zoya A. Solodovnikova, Konstantin V. Pokholok, Sergey Yu. Stefanovich, Bogdan I. Lazoryak, Elena G. Khaikina
Source
Journal of Solid State Chemistry
Volume: 220, Pages: 217–220
Time of Publication: 2014
Abstract A new triple molybdate Na25Cs8Fe5(MoO4)24 was synthesized using solid state reactions and studied with X-ray powder diffraction, second harmonic generation (SHG) technique, differential scanning calorimetry, Mssbauer and dielectric impedance spectroscopy. Single crystals of Na25Cs8Fe5(MoO4)24 were obtained and its structure was solved (the space group P View the MathML source1, a=12.5814(5), b=13.8989(5), c=28.4386(9) , α=90.108(2), β=90.064(2), γ=90.020(2), V=4973.0(3) 3, Z=2, R=0.0440). Characteristic features of the structure are polyhedral layers composed of pairs of edge-shared FeO6 and (Fe, Na)O6 octahedra, which are connected by bridging МоО4 tetrahedra. The layers share common vertices with bridging МоО4 tetrahedra to form an open 3D framework with the cavities occupied by the Cs+ and Na+ cations. The compound undergoes first-order phase transformation at 642 K and above this phase transition, electrical conductivity reaches 10−3–10−2 S cm−1. Thus, Na25Cs8Fe5(MoO4)24 may be considered as a promising compound for developing new materials with high ionic conductivity.
Keywords Triple molybdate; Sodium; Synthesis; Crystal structure; Phase transition; Ionic conductivity
Remark DOI: 10.1016/j.jssc.2014.09.004
Link

Hydrogen permeability of SrCe0.7Zr0.25Ln0.05O3−δ membranes (Ln=Tm and Yb)

Authors Wen Xing, Paul Inge Dahl, Lasse Valland Roaas, Marie-Laure Fontaine, Yngve Larring, Partow P. Henriksen, Rune Bredesen
Source
Journal of Membrane Science
Volume: 473, Pages: 327–332
Time of Publication: 2015
Abstract Zr substituted acceptor doped SrCeO3 materials were synthesized by citric acid route and characterized by XRD and SEM. The hydrogen flux of the materials was measured as a function of temperature and hydrogen partial pressure on the feed side. The hydrogen permeability for SrCe0.7Zr0.25Tm0.05O3−δ and SrCe0.7Zr0.25Yb0.05O3−δ is similar under our measurement window and shows the same hydrogen partial pressure dependency. Under short circuit condition, the hydrogen permeability increased significantly by more than one order of magnitude indicating that the hydrogen transport is limited by electronic conduction under open circuit conditions. The observed data were discussed by applying defect chemistry and the conventional ambipolar transport theory. After the hydrogen permeation measurements, the indication of kinetic cation de-mixing was found by XRD analysis.
Keywords Co-substitution of B site; Hydrogen flux; Permeability; Acceptor doping; SrCeO3
Remark DOI: 10.1016/j.memsci.2014.09.027
Link

Superior electrochemical performance and oxygen reduction kinetics of layered perovskite PrBaxCo2O5+δ (x = 0.90–1.0) oxides as cathode materials for intermediate-temperature solid oxide fuel cells

Authors Jingping Wang, Fuchang Meng, Tian Xia, Zhan Shi, Jie Lian, Chunbo Xu, Hui Zhao, Jean-Marc Bassat, Jean-Claude Grenier
Source
International Journal of Hydrogen Energy
Time of Publication: 2014
Abstract The layered perovskite PrBaxCo2O5+δ (PBxCO, x = 0.90–1.0) oxides have been synthesized by a solid-state reaction technique, and evaluated as the potential cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). Room temperature X-ray diffraction patterns show the orthorhombic structures which double the lattice parameters from the perovskite cell parameter as a ≈ ap, b ≈ ap and c ≈ 2ap (ap is the cell parameter of the primitive perovskite) in the Pmmm space group. There is a good chemical compatibility between the PBxCO cathode and the Ce0.9Gd0.1O1.95 (CGO) electrolyte at 1000 C. The electrical conductivity and thermal expansion coefficient of PBxCO are improved due to the increased amount of electronic holes originated from the Ba-deficiency. The results demonstrate the high electrochemical performance of PBxCO cathodes, as evidenced by the super low polarization resistances (Rp) over the intermediate temperature range. The lowest Rp value, 0.042 Ω cm2, and the cathodic overpotential, −15 mV at a current density of −25 mA cm−2, are obtained in the PrBa0.94Co2O5+δ cathode at 600 C in air, which thus allow to be used as a highly promising cathode for IT-SOFCs. A CGO electrolyte fuel cell with the PrBa0.94Co2O5+δ cathode presents the attractive peak power density of ∼1.0 W cm−2 at 700 C. Furthermore, the oxygen reduction kinetics of the PrBa0.94Co2O5+δ cathode is also studied, and the rate-limiting steps for oxygen reduction reaction are determined at different temperatures.
Remark DOI: 10.1016/j.ijhydene.2014.09.041
Link

Organic–Inorganic Hybrid Membranes Based on Sulfonated Poly(ether ether ketone) and Tetrabutylphosphonium Bromide Ionic Liquid for PEM Fuel Cell Applications

Authors Vijay Shankar Rangasamy, Savitha Thayumanasundaram, Niels de Greef, Jin Won Seo and Jean-Pierre Locquet
Source
European Journal of Inorganic Chemistry
Time of Publication: 2014
Abstract Ionic liquids (ILs), with their inherent ionic conductivity and negligible vapor pressure, can be exploited in proton exchange membrane (PEM) fuel cells for which thermal management is a major problem and the cell operation temperature is limited by the boiling point of water. In this work, sulfonated poly(ether ether ketone) (SPEEK) membranes were modified by the incorporation of tetrabutylphosphonium bromide ([P4 4 4 4]Br) by solvent-casting. Electrochemical impedance spectroscopy (EIS) was used to study the electrical properties of the modified membranes. Simultaneous TGA and FTIR studies were used to evaluate the thermal stability and chemical structure of the modified membranes, respectively. 1H NMR spectroscopy was applied to probe the changes in the chemical environment due to the interaction between the ionic liquid and the polymer. Mechanical properties were studied by dynamic mechanical analysis. The temperature-dependent behavior of the viscosity of the [P4 4 4 4]Br ionic liquid was observed to obey the Vogel–Fulcher–Tammann (VFT) equation, and was correlated to the ion-conducting properties of the IL-doped SPEEK membranes.
Remark DOI: 10.1002/ejic.201402558
Link

Crystal Structure and electrical properties of complex perovskite solid solutions based on (1-x) NaNbO3-xBi (Zn0.5Ti0.5) O3

Authors Sasiporn Prasertpalichat, David P. Cann
Source
Journal of Electroceramics
Time of Publication: 2014
Abstract Ceramics based on the perovskite solid solution (1-x) NaNbO3-xBi (Zn0.5Ti0.5) O3 were prepared using conventional solid state synthesis. The crystal structure, electrical, and optical properties were examined. According to diffraction data, a single perovskite phase could be identified up to the composition x = 0.09. As the Bi (Zn0.5Ti0.5) O3 content increased the crystal structure transitioned from orthorhombic to pseudocubic symmetry. Furthermore, dielectric data showed that the dielectric maximum shifted to lower temperatures with the addition of Bi (Zn0.5Ti0.5) O3. Polarization hysteresis data revealed a slim linear loop across the whole range of solid solutions. Optical data also showed a decrease in the optical band gap from 3.4 eV for pure NaNbO3 to 2.9 eV for the x = 0.09 composition. Using impedance spectroscopy, an electrically inhomogeneous microstructure was observed for compositions with increased Bi (Zn0.5Ti0.5) O3 content. Finally, the substitution of Ta on the B-site was shown to shift the dielectric maximum to temperatures as low as 100 K.
Remark DOI 10.1007/s10832-014-9953-x
Link

A family of oxide ion conductors based on the ferroelectric perovskite Na0.5Bi0.5TiO3

Authors Ming Li, Martha J. Pietrowski, Roger A. De Souza, Huairuo Zhang, Ian M. Reaney, Stuart N. Cook, John A. Kilner & Derek C. Sinclair
Source
Nature Materials
Volume: 13, Pages: 31-35
Time of Publication: 2014
Abstract Oxide ion conductors find important technical applications in electrochemical devices such as solid-oxide fuel cells (SOFCs), oxygen separation membranes and sensors1, 2, 3, 4, 5, 6, 7, 8, 9. Na0.5Bi0.5TiO3 (NBT) is a well-known lead-free piezoelectric material; however, it is often reported to possess high leakage conductivity that is problematic for its piezo- and ferroelectric applications10, 11, 12, 13, 14, 15. Here we report this high leakage to be oxide ion conduction due to Bi-deficiency and oxygen vacancies induced during materials processing. Mg-doping on the Ti-site increases the ionic conductivity to ~0.01 S cm−1 at 600 C, improves the electrolyte stability in reducing atmospheres and lowers the sintering temperature. This study not only demonstrates how to adjust the nominal NBT composition for dielectric-based applications, but also, more importantly, gives NBT-based materials an unexpected role as a completely new family of oxide ion conductors with potential applications in intermediate-temperature SOFCs and opens up a new direction to design oxide ion conductors in perovskite oxides.
Remark doi:10.1038/nmat3782
Link

Thermoelectric Properties of A-site Deficient Lanthanum Substituted Strontium Titanate

Author Thomas Emdal Loland
Source
Time of Publication: 2014
Remark Link

Grain Size Dependent Comparison of ZnO and ZnGa2O4 Semiconductors by Impedance Spectrometry

Authors Shalima Shawuti, Musa Mutlu Can, Mehmet Ali Glgn,Tezer Fırat
Source
Electrochimica Acta
Time of Publication: 2014
Abstract We investigated the electrical properties of ZnGa2O4 via AC (alternating current) Impedance Spectroscopy method comparing with ZnO reference material. Experimentally, AC electrical conductivity of ZnO and ZnGa2O4 were found to be a function of temperature and grain size; i.e., the increase in grain size of the ZnO led a decrease in room temperature conductivity from 1.35 10−7 S cm−1 to 9.9 10−8 S cm−1. The temperature dependent resistivity variation of ZnGa2O4 and ZnO were similar to each other with varied responding temperature. Likewise, the conductivity for ZnGa2O4 decrease from 2.2 10−8 S cm−1 to 3.8 10−9 S cm−1 upon an increase in grain size from ∼0.5 μm to 100 μm, accordingly. In addition, a rise in temperature caused an increase in conductivity and led to a corresponding shift in the relaxation time towards the lower values. The semicircles in Nyquist plots disappeared at temperature above 250 C and 700 C for ZnO and ZnGa2O4, respectively. The AC measurements were also correlated with the size dependent activation energies (171 meV for 0.5 μm ZnO and 1200 meV for 0.5 μm ZnGa2O4).
Keywords Activation energy; Nyquist plots; AC Impedance spectrometry; Oxide semiconductors
Remark DOI: 10.1016/j.electacta.2014.08.084
Link

Effect of thermobaric treatment on the structure and properties of CaCu3Ti4O12

Authors N. I. Kadyrova, Y. G. Zainulin, N. V. Mel’nikova, I. S. Ustinova, I. G. Grigorov
Source
Bulletin of the Russian Academy of Sciences: Physics
Volume: 78, Issue: 8, Pages: 719-722
Time of Publication: 2014
Abstract CaCu3Ti4O12 is prepared by means of solid-state sintering. The effect of thermobaric treatment (P = 8.0 GPa and T = 1100C) and partial replacement of titanium by vanadium on the microstructure and dielectric properties of CaCu3Ti4O12 are investigated.
Remark Link

Conductivity and oxygen reduction activity changes in lanthanum strontium manganite upon low-level chromium substitution

Authors George Tsekouras, Artur Braun
Source
Solid State Ionics
Volume: 266, Pages: 19-24
Time of Publication: 2014
Abstract On the timescale of solid oxide fuel cell (SOFC) system lifetime requirements, the thermodynamically predicted low-level substitution of chromium on the B-site of (La,Sr)MnO3 could be a source of cathode degradation underlying more overt and well-known chromium poisoning mechanisms. To study this phenomenon in isolation, electronic conductivity (σ) and electrochemical oxygen reduction activity of the (La0.8Sr0.2)0.98CrxMn1−xO3 model series (x = 0, 0.02, 0.05 or 0.1) were measured in air between 850 and 650 C. Depending on the extent of chromium substitution and the measurement temperature, electrochemical impedance spectroscopy (EIS) results could be deconvoluted into a maximum of three contributions reflecting possible limiting processes such as oxide ion transport and dissociative adsorption. Chromium substitution resulted in lowered σ (from 174 S cm− 1 (x = 0) to 89 S cm− 1 (x = 0.1) at 850 C) and a steady rise in associated activation energy (Ea) (from 0.105 0.001 eV (x = 0) to 0.139 0.001 eV (x = 0.1)). From EIS analyses, ohmic and polarisation resistances increased, whilst Ea for the overall oxygen reduction reaction also increased from 1.39 0.04 eV (x = 0) to 1.48–1.54 0.04 eV upon chromium substitution.
Keywords Solid oxide fuel cell; Lanthanum strontium manganite; Chromium poisoning; Electronic conductivity; Electrochemical impedance spectroscopy
Remark Link

The effect of calcination temperature on the electrochemical properties of La0.3Sr0.7Fe0.7Cr0.3O3−x (LSFC) perovskite oxide anode of solid oxide fuel cells (SOFCs)

Authors Yifei Sun, Ning Yan, Jianhui Li, Huayi Wu, Jing-Li Luo, Karl T. Chuang
Source
Sustainable Energy Technologies and Assessments
Volume: 8, Pages: 92-98
Time of Publication: 2014
Abstract A series of perovskite structure anode materials, LSFC, was successfully prepared by a glycine combustion process and further calcined at different temperatures. The electrochemical properties of anodes prepared at various calcination temperatures (1100 C, 1200 C and 1300 C) were investigated. The calcination temperature had no significant influence on the morphology of the material but showed obvious influences on the particle sizes and electrochemical properties of the materials. Higher calcination temperature results in sharper X-ray diffractometer (XRD) diffraction peaks of the materials with larger particle sizes and higher electrical conductivity. However materials calcined at higher temperature had much smaller BET surface area resulting in lower triple phase boundary (TPB). The electrochemical performance test exhibited that LSFC anode material sintered at 1100 C exhibited the smallest area specific resistance (ASR) value in H2 at operating temperatures from 700 to 900 C. For proton conducting SOFCs (PC-SOFCs) fed by syngas, the cell with anode calcined at 1100 C also showed highest power density output of 120 mW/cm2 at 750 C, which was almost three times higher than that of the cell with anode calcined at 1300 C.
Keywords Solid oxide fuel cell; Calcination temperature; Electrochemical properties; Perovskite
Remark Link

Oxygen interstitial and vacancy conduction in symmetric Ln2 x Zr2 x O7 x/2 (Ln = Nd, Sm) solid solutions

Authors A. V. Shlyakhtina, D. A. Belov, A. V. Knotko, I. V. Kolbanev, A. N. Streletskii, O. K. Karyagina, L. G. Shcherbakova
Source
Inorganic Materials
Volume: 50, Issue: 10, Pages: 1035-1049
Time of Publication: 2014
Abstract We have compared (Ln2 − x Zr x )Zr2O7 + x/2 (Ln = Nd, Sm) pyrochlore-like solid solutions with interstitial oxide ion conduction and Ln2(Zr2 − x Ln x )O7 − δ (Ln = Nd, Sm) pyrochlore-like solid solutions with vacancy-mediated oxide ion conduction in the symmetric systems Nd2O3-ZrO2 (NdZrO) and Sm2O3-ZrO2 (SmZrO). We have studied their structure, microstructure, and transport properties and determined the excess oxygen content of the (Sm2 − x Zr x )Zr2O7 + x/2 (x = 0.2) material using thermal analysis and mass spectrometry in a reducing atmosphere (H2/Ar-He). The Ln2 x Zr2 x O7 x/2 (Ln = Nd, Sm) solid solutions have almost identical maximum oxygen vacancy and interstitial conductivities: (3–4) 10−3 S/cm at 750C. The lower oxygen vacancy conductivity of the Ln2(Zr2 − x Ln x )O7 − δ (Ln = Nd, Sm; 0 < x ≤ 0.3) solid solutions is due to the sharp decrease in it as a result of defect association processes, whereas the interstitial oxide ion conductivity of the (Ln2 − x Zr x )Zr2O7 + x/2 (Ln = Nd, Sm; 0.2 ≤ x < 0.48) pyrochlore-like solid solutions is essentially constant in a broad range of Ln2O3 concentrations.
Remark Link

MICROWAVE SINTERING OF Sr AND Mg-DOPED LANTHANUM GALLATE (LSGM) SOLID ELECTROLYTES

Authors Cristian Andronescu, Victor Fruth, Enikoe Volceanov, Rares Scurtu, Cornel Munteanu, Maria Zaharescu
Source
Romanian journal of materials
Time of Publication: 2014-01
Abstract Sr2+ and Mg2+ simultaneously doped lanthanum gallate (LSGM) powders, prepared by a modified Pechini route using polyvinyl alcohol (PVA) as polymeric alcohol, were densified using an activated microwave technique at 2.45 GHz, to develop a dense stable electrolyte for application in intermediate temperatures solid oxide fuel cells (IT-SOFC). Thermal behaviour of precursors was investigated by means of differential thermal analysis combined with thermogravimetric analysis (DTA/TGA). The powders and sintered samples were characterized using scanning electron microscopy and energy dispersive analysis (SEM-EDAX), X-ray diffraction (XRD) and infrared spectroscopy (FT-IR). The thermal expansion coefficient (TEC) and ionic conductivity of the sintered samples were also evaluated. Fine, homogeneous and high density pellets of almost pure LSGM phase were obtained after sintering at 14000C for a short period time in an activated microwave field. Using activated microwave field, due to the volumetric in situ heating, the sintering process is highly specific and instantaneous, leading to a faster kinetics compared to the conventional process (electric oven). With an optimized sintering schedule, a fine grained and dense microstructure of the samples were obtained.
Remark Link

Magnetron formation of Ni/YSZ anodes of solid oxide fuel cells

Authors A. A. Solov’ev, N. S. Sochugov, I. V. Ionov, A. V. Shipilova, A. N. Koval’chuk
Source
Russian Journal of Electrochemistry
Volume: 50, Issue: 7, Pages: 647-655
Time of Publication: 2014
Abstract Physico-chemical and structural properties of nanocomposite NiO/ZrO2:Y2O3 (NiO/YSZ) films applied using the reactive magnetron deposition technique are studied for application as anodes of solid oxide fuel cells. The effect of oxygen consumption and magnetron power on the discharge parameters is determined to find the optimum conditions of reactive deposition. The conditions for deposition of NiO/YSZ films, under which the deposition rate is maximum (12 μm/h), are found and the volume content of Ni is within the range of 40–50%. Ni-YSZ films reduced in a hydrogen atmosphere at the temperature of 800C have a nanoporous structure. However, massive nickel agglomerates are formed in the course of reduction on the film surface; their amount grows at an increase in Ni content in the film. Solid oxide fuel cells with YSZ supporting electrolyte and a LaSrMnO3 cathode are manufactured to study electrochemical properties of NiO/YSZ films. It is shown that fuel cells with a nanocomposite NiO/YSZ anode applied using a magnetron sputtering technique have the maximum power density twice higher than in the case of fuel cells with an anode formed using the high-temperature sintering technique owing to a more developed gas-anode-electrolyte three-phase boundary.
Remark Link

Full ceramic micro solid oxide fuel cells: towards more reliable MEMS power generators operating at high temperatures

Authors I. Garbayo, D. Pla, A. Morata, L. Fonseca, N. Sabat and A. Tarancn
Source
Energy Environ. Sci.
Time of Publication: 2014
Abstract Batteries, with a limited capacity, have dominated the power supply of portable devices for decades. Recently, the emergence of new types of highly efficient miniaturized power generators like micro fuel cells has opened up alternatives for continuous operation on the basis of unlimited fuel feeding. This work addresses for the first time the development of a full ceramic micro solid oxide fuel cell fabricated in silicon technology. This full-ceramic device represents a new generation of miniaturized power generators able to operate at high temperatures, and therefore able to work with a hydrocarbon fuel supply. Dense yttria-stabilized zirconia free-standing large-area membranes on micromachined silicon were used as the electrolyte. Thin-film porous electrodes of La0.6Sr0.4CoO3−δ and gadolinia-doped ceria were employed as cathode and anode materials, respectively. The electrochemical performance of all the components was evaluated by partial characterization using symmetrical cells, yielding excellent performance for the electrolyte (area specific resistance of 0.15 Ω cm2 at temperatures as low as 450 C) and the electrodes (area specific resistance of the cathode and anode below 0.3 Ω cm2 at 700 C). A micro solid oxide fuel cell with an active area of 2 mm2 and less than 1 micrometer in thickness was characterized under fuel cell conditions, using hydrogen as a fuel and air as an oxidant. A maximum power density of 100 mW cm−2 and 2 mW per single membrane was generated at 750 C, having an open circuit voltage of 1.05 V. Impedance spectroscopy of the all-ceramic membrane showed a total area-specific resistance of [similar]3.5 Ω cm2.
Remark DOI: 10.1039/C4EE00748D
Link

Proton conductivity of hexagonal and cubic BaTi1−xScxO3−δ (0.1 ≤ x ≤ 0.8)

Authors Seikh M. H. Rahman, Stefan T. Norberg, Christopher S. Knee, Jordi J. Biendicho, Stephen Hull and Sten G. Eriksson
Source
Dalton Transactions
Time of Publication: 2014
Abstract BaTi1−xScxO3−δ (x = 0.1–0.8) was prepared via solid state reaction. High resolution X-ray powder diffraction was used to characterise the synthesised materials. It was found that low substitution (x = 0.1 and 0.2) of Ti4+ for Sc3+ gives a hexagonal perovskite structure, whereas high substitution (x = 0.5–0.7) results in a cubic perovskite structure. Thermogravimetric analysis revealed significant levels of protons in both as-prepared and hydrated samples. Electrical conductivity was measured by AC impedance methods under oxygen, argon and under dry and humid, both H2O and D2O, conditions for BaTi1−xScxO3−δ (x = 0.2, 0.6 and 0.7). In the temperature range of 150–600 C, under humid conditions, the conductivity is significantly higher than that under the dry conditions. The increase in conductivity is especially prominent for the cubic phases, indicating that protons are the dominant charge carriers. The proton conductivity of hexagonal BaTi0.8Sc0.2O3−δ is approx. two orders of magnitude lower than that of the more heavily substituted cubic phases. Conductivity is also found to be higher in dry O2 than in Ar in the whole temperature range of 150–1000 C, characteristic of a significant contribution from p-type charge carriers under oxidising atmospheres. Greater Sc3+ substitution leads to a higher proton concentration and the highest proton conductivity (σ [similar] 2 10−3 S cm−1 at 600 C) is found for the BaTi0.3Sc0.7O3−δ composition.
Remark DOI: 10.1039/C4DT01280A
Link

Protons in acceptor doped langasite, La3Ga5SiO14

Authors Tor Svendsen Bjrheim, Reidar Haugsrud, Truls Norby
Source
Solid State Ionics
Volume: 264, Pages: 76–84
Time of Publication: 2014
Abstract The electrical and defect chemical properties of acceptor doped langasite have been investigated over wide ranges of pH2O, pO2 and temperature. All compositions are pure proton conductors up to 800 C in wet atmospheres and mixed oxide ion-p-type conductors at higher temperatures. The enthalpy of mobility of protons is 75 3 kJ/mol, while that of oxygen vacancies is 125 7 kJ/mol. The standard enthalpy and entropy of hydration are -100 3 kJ/mol and -157 5 J/mol K, respectively. Langasite based sensors may therefore be affected by dissolution of protons from H2O in the bulk crystal lattice up to temperatures as high as 1000 C.
Keywords Langasite; Piezoelectric; DFT; Defects; Hydrogen; Conductivity

Solid-State Synthesis and Properties of Relaxor (1−x)BKT–xBNZ Ceramics

Authors Espen T. Wefring, Maxim I. Morozov, Mari-Ann Einarsrud and Tor Grande
Source
J. of American Ceramic Society
Time of Publication: 2014
Abstract Conventional solid-state synthesis was used to synthesize dense and phase pure ceramics in the (1−x) Bi0.5K0.5TiO3–xBi0.5Na0.5ZrO3 (BKT–BNZ) system. Structural characterization was done using X-ray diffraction at both room temperature and elevated temperatures, identifying a transition from tetragonal xBi0.5Na0.5ZrO3 (xBNZ, x = 0–0.10) to pseudo cubic xBNZ for x = 0.15–0.80. Dielectric properties were investigated with respect to both temperature (RT = 600C) and frequency (1–106 Hz). Relaxor-like behavior was retained for all the materials investigated, evident by the broadening of the relative dielectric permittivity peaks at transition temperatures as well as frequency dispersion at their maximum. The maximum dielectric constant at elevated temperature was found for 0.15 BNZ. Electric field-induced strain and polarization response were also investigated for several compositions at RT and the largest field-induced strain was observed for the 0.10 BNZ ceramics. The composition range with best performance coincides with the transition from tetragonal to cubic crystal structure.
Remark DOI: 10.1111/jace.13066
Link

Ceramic–carbonate dual-phase membrane with improved chemical stability for carbon dioxide separation at high temperature

Authors Tyler T. Norton, Y.S. Lin
Source
Solid State Ionics
Volume: 263, Pages: 172–179
Time of Publication: 2014
Abstract This study examines membrane synthesis, structural stability, permeation properties, and long-term permeation stability of a new dense dual-phase membrane of composition La0.85Ce0.1Ga0.3Fe0.65Al0.05O3 − δ (LCGFA)–carbonate for high temperature CO2 separation. Porous ceramic supports made by sintering pressed powder at a temperature below its densification temperature resulted in a desired support with an open porosity ranging between 40 and 50%. The dual-phase membranes was prepared by direct infiltration of the ceramic supports in molten carbonate at 600 C, resulting in a four order of magnitude decrease in permeance when compared to the support. LCGFA–carbonate membranes are stable when exposed to gases ranging from gas mixtures containing N2 and various concentrations of CO2 to simulated syngas, and exhibit a stable long term CO2 permeation flux of 0.025 mLmin− 1cm− 2 for more than 275 h at 900 C. The CO2 permeation results show exponential dependence to increasing system temperature as well as a linear dependence to logarithmic change in CO2 partial pressure gradients across the membrane in the CO2 pressure range studied.
Keywords Ceramic–carbonate; Carbon dioxide permeation; Dual-phase membrane; Perovskite
Remark Link

Hydrogen flux in La0.87Sr0.13CrO3–δ

Authors Camilla K. Vigen, Reidar Haugsrud
Source
Journal of Membrane Science
Volume: 468, Pages: 317–323
Time of Publication: 2014
Abstract Acceptor doped LaCrO3 is a promising material for dense, ceramic hydrogen permeable membranes, displaying hydrogen flux in the order of 10−4 ml min−1 cm−1 in a 10% H2+2.5% H2O/dry Ar gradient at 1000 C. In this work we have characterized the ambipolar proton electron hole conductivity in La0.87Sr0.13CrO3–δ by means of hydrogen flux measurements. Proton transport parameters were extracted, yielding a pre-exponential factor of 3 cm2 K V−1 s−1 and an enthalpy of mobility of 65 kJ mol−1. Hydrogen flux measurements showed that applying a layer of Pt on both feed and sweep side surfaces significantly altered the temperature dependency and increased the hydrogen flux in a 550 μm thick membrane. This indicates that surface kinetics will limit the hydrogen flux in uncoated membranes. From hydrogen surface exchange measurements, a surface exchange coefficient ranging from 10−10 to 10−8 mol cm−2 s−1 at 325–600 C was obtained.
Keywords Hydrogen permeation; LaCrO3; Proton conductivity; Surface kinetics
Remark Link

Carbon dioxide permeation properties and stability of samarium-doped-ceria carbonate dual-phase membranes

Authors Tyler T. Norton, Bo Lu, Y.S. Lin
Source
Journal of Membrane Science
Volume: 467, Pages: 244–252
Time of Publication: 2014
Abstract This study examines high temperature carbon dioxide permeation properties and long-term permeation stability of samarium doped ceria (SDC)-carbonate dual-phase membranes. Hermetic SDC-carbonate membranes were prepared by infiltrating porous SDC ceramic support with Li/K/Na molten carbonate. Carbon permeation experiments on the SDC-carbonate membranes were conducted with either atmospheric or high pressure feed of CO2:N2 mixture or simulated syngas with composition of 50% CO, 35% CO2, 10% H2, and 5% N2. The SDC-carbonate membranes exhibit CO2 permeation flux in the range of 0.2–0.8 mL(STP) cm−2 min−1 in 700–950 C with measured CO2 to N2 separation factor above 1000. The CO2 permeation flux shows power function dependence with CO2 partial pressure and exponential dependence with temperature. The activation energy for CO2 permeation is 63 kJ mol−1, similar to that for oxygen ionic conduction in SDC. Essentially the same CO2 permeation characteristics are observed for the membranes with CO2:N2 and simulated syngas feeds. The membranes exhibit stable long-term permeation flux in 700–900 C with either CO2:N2 or simulated gas feed at atmospheric pressure or high pressure (5 atm) for various periods of testing time (as long as 35 days). The membranes, with remarkable permeation stability in the presence of H2, show only slight decomposition of the ceramic phase after long-term exposure to feed gas mixtures at high temperature.
Keywords Ceramic-carbonate; Samarium doped ceria; Carbon dioxide permeation; Fluorite; Membrane stability
Remark Link

Hydrogen permeation characteristics of La27Mo1.5W3.5O55.5

Authors Einar Vllestad, Camilla K. Vigen, Anna Magras, Reidar Haugsrud
Source
Journal of Membrane Science
Volume: 461, Pages: 81–88
Time of Publication: 2014
Abstract Hydrogen permeation in 30% Mo-substituted lanthanum tungsten oxide membranes, La27Mo1.5W3.5O55.5 (LWMo), has been measured as a function of temperature, hydrogen partial pressure gradient, and water vapor pressure in the sweep gas. Transport of hydrogen by means of ambipolar proton–electron conductivity and – with wet sweep gas – water splitting contributes to the measured hydrogen content in the permeate. At 700 C under dry sweep conditions, the H2 permeability in LWMo was 610−4610−4 mL min−1 cm-1, which is significantly higher than that for state-of-the-art SrCeO3-based membranes. Proton conductivity was identified as rate limiting for ambipolar bulk transport across the membrane. On these bases it is evident that Mo-substitution is a successful doping strategy to increase the n-type conductivity and H2 permeability compared to nominally unsubstituted lanthanum tungsten oxide. A steady-state model based on the Wagner transport theory with partial conductivities as input parameters predicted H2 permeabilities in good agreement with the measured data. LWMo is a highly competitive mixed proton–electron conducting oxide for hydrogen transport membrane applications provided that long term stability can be ensured.
Remark http://dx.doi.org/10.1016/j.memsci.2014.03.011
Link

Mesoporous NiO-Samaria Doped Ceria for Low-Temperature Solid Oxide Fuel Cells

Authors Kim, Jin-Yeop; Kim, Ji Hyeon; Choi, Hyung Wook; Kim, Kyung Hwan; Park, Sang Joon
Source
Journal of Nanoscience and Nanotechnology
Volume: 14, Issue: 8, Pages: 6399-6403(5)
Time of Publication: 2014
Abstract In order to prepare anode material for low-temperature solid oxide fuel cells (SOFCs), the mesoporous NiO-SDC was synthesized using a cationic surfactant (cetyltrimethyl-ammonium bromide; CTAB) for obtaining wide triple-phase boundary (TPB). In addition, Ni-SDC anode-supported SOFC single cells with YSZ electrolyte and LSM cathode were fabricated and the performance of single cells was evaluated at 600 C. The microstructure of NiO-SDC was characterized by XRD, EDX, SEM, and BET, and the results showed that the mesoporous NiO-SDC with 10 nm pores could be obtained. It was found that the surface area and the electrical performance were strongly influenced by the Ni content in Ni-SDC cermets. After calcined at 600 C, the surface area of NiO-SDC was between 90–117 m2/g at 35–45 Ni wt%, which was sufficiently high for providing large TPB in SOFC anode. The optimum Ni content for cell performance was around 45 wt% and the corresponding MPD was 0.36 W/cm2. Indeed, the mesoporous NiO-SDC cermet may be of interest for use as an anode for low-temperature SOFCs.
Remark DOI: http://dx.doi.org/10.1166/jnn.2014.8452
Link

Oxide ion transport in (Nd2−xZrx)Zr2O7+δ electrolytes by an interstitial mechanism

Authors A.V. Shlyakhtina, D.A. Belov, A.V. Knotko, M. Avdeev, I.V. Kolbanev, G.A. Vorobieva, O.K. Karyagina, L.G. Shcherbakova
Source
Journal of Alloys and Compounds
Volume: 603, Issue: 5, Pages: 274–281
Time of Publication: 2014
Abstract We have studied the structure and transport properties of ten (Nd2−xZrx)Zr2O7+x/2 (x = 0–1.27) solid solutions, which lie in the ZrO2–Nd2Zr2O7 isomorphous miscibility range. Major attention has been focused on the pyrochlore-like (Nd2−xZrx)Zr2O7+x/2 solid solutions with x = 0–0.78, which are thought to be potential interstitial oxide ion conductors. The X-ray and neutron diffraction results demonstrate that the (Nd2−xZrx)Zr2O7+x/2 (x = 0–1.27) solid solutions undergo an order–disorder (pyrochlore–defect fluorite) structural phase transition. The (Nd2−xZrx)Zr2O7+x/2 (x = 0.2–0.78) have the bulk conductivity, ∼(1.2–4) 10–3 S/cm at 750 C, which is two orders of magnitude higher than that of the ordered pyrochlore Nd2Zr2O7. An attempt has been made to determine the interstitial oxygen content of (Nd2−xZrx)Zr2O7+x/2 (x = 0.2; 0.67) in a reducing atmosphere using thermogravimetry and mass spectrometry. It has been shown that no reduction occurs in the NdZrO system, where neodymium has only one oxidation state, 3+.
Keywords Fuel cells; Ionic conduction; Electrochemical impedance spectroscopy; Neutron diffraction; X-ray diffraction; SEM
Remark http://dx.doi.org/10.1016/j.jallcom.2014.03.068
Link

Application of PVD methods to solid oxide fuel cells

Authors A.A. Solovyeva, N.S. Sochugov, S.V. Rabotkin, A.V. Shipilova, I.V. Ionov, A.N. Kovalchuk, A.O. Borduleva
Source
Applied Surface Science
Time of Publication: 2014
Abstract In this paper, attention is paid to the application of such a method of vacuum physical vapor deposition (PVD) as magnetron sputtering for fabrication of a solid oxide fuel cell (SOFC) materials and structures. It is shown that the YSZ (yttria-stabilized zirconia) electrolyte and Ni–YSZ anode layers with required thickness, structure and composition can be effectively formed by PVD methods. The influence of parameters of pulsed power magnetron discharge on the deposition rate and the microstructure of the obtained YSZ electrolyte films were investigated. It is shown that the deposition rate of the oxide layers by magnetron sputtering can be significantly increased by using asymmetric bipolar power magnetrons, which creates serious prerequisites for applying this method on the industrial scale. Porous Ni–YSZ anode films were obtained by reactive co-sputtering of Ni and Zr–Y targets and subsequent reduction in the H2 atmosphere at a temperature of 800 C. The Ni–YSZ films comprised small grains and pores of tens of nanometers.
Keywords Solid oxide fuel cell; Metal support; Magnetron sputtering; Thin film; YSZ electrolyte; NiO/YSZ anode
Remark http://dx.doi.org/10.1016/j.apsusc.2014.03.163
Link

Proton conduction in oxygen deficient Ba3In1.4Y0.3M0.3ZrO8 (M = Ga3+ or Gd3+) perovskites

Authors Francis G. Kinyanjui, Stefan T. Norberg, Christopher S. Knee, Sten-G. Eriksson
Source
Journal of Alloys and Compounds
Volume: 605, Pages: 56-62
Time of Publication: 2014
Abstract B -site disordered, oxygen deficient Ba3In1.4Y0.3M 0.3ZrO8 (M = Gd3+ or Ga3+) perovskites of space group View the MathML sourcePm3‾m, were prepared by a solid-state reactive sintering method. Thermogravimetric analysis of the as-prepared samples revealed 79.3% and 55.5% protonation of the available oxygen vacancies by OH groups in the Gd3+ and Ga3+ containing samples, respectively. Conductivity was found to be in the range of 0.3–1.1 10−3 S cm−1 (M = Gd3+) and 1.1–4.6 10−4 S cm−1 (M = Ga3+) for the temperature interval 300–600 C in wet Argon. Ba3In1.4Y0.3Ga0.3ZrO8 shows an approximate one order of magnitude increase in conductivity at T > 600 C under dry oxygen indicating a significant p-type contribution whereas Ba3In1.4Y0.3Gd0.3ZrO8 reveals a smaller enhancement. Ba3In1.4Y0.3Ga0.3ZrO8 displays considerable mixed proton–electronic conduction in the interval 400–800 C under wet oxidising conditions suggesting possibility of Ga-containing compositions as a cathode materials in a proton conducting fuel cell.
Keywords Proton conducting electrolyte; Oxygen deficient perovskite; Mixed conductor; Cathode material; Impedance spectroscopy

Role of point defects in bipolar fatigue behavior of Bi(Mg1/2Ti1/2)O3 modified (Bi1/2K1/2)TiO3-(Bi1/2Na1/2)TiO3 relaxor ceramics

Authors Nitish Kumar, Troy Y. Ansell and David P. Cann
Source
J. Applied Physics
Volume: 115, Pages: 154104
Time of Publication: 2014
Abstract Lead-free Bi(Mg1/2Ti1/2)O3-(Bi1/2K1/2)TiO3-(Bi1/2 Na 1/2)TiO3 (BMT-BKT-BNT) ceramics have been shown to exhibit large electromechanical strains under high electric fields along with negligible fatigue under strong electric fields. To investigate the role of point defects on the fatigue characteristics, the composition 5BMT-40BKT-55BNT was doped to incorporate acceptor and donor defects on the A and B sites by adjusting the Bi/Na and Ti/Mg stoichiometries. All samples had pseudo-cubic symmetries based on x-ray diffraction, typical of relaxors. Dielectric measurements showed that the high and low temperature phase transitions were largely unaffected by doping. Acceptor doping resulted in the observation of a typical ferroelectric-like polarization with a remnant polarization and strain hysteresis loops with significant negative strain. Donor-doped compositions exhibited characteristics that were indicative of an ergodic relaxor phase. Fatigue measurements were carried out on all of the compositions. While the A-site acceptor-doped composition showed a small degradation in maximum strain after 106 cycles, the other compositions were essentially fatigue free. Impedance measurements were used to identify the important conduction mechanisms in these compositions. As expected, the presence of defects did not strongly influence the fatigue behavior in donor-doped compositions owing to the nature of their reversible field-induced phase transformation. Even for the acceptor-doped compositions, which had stable domains in the absence of an electric field at room temperature, there was negligible degradation in the maximum strain due to fatigue. This suggests that either the defects introduced through stoichiometric variations do not play a prominent role in fatigue in these systems or it is compensated by factors like decrease in coercive field, an increase in ergodicity, symmetry change, or other factors.
Remark http://dx.doi.org/10.1063/1.487167
Link

Structure and transport properties in un-doped and acceptor-doped gadolinium tungstates

Authors Wen Xing, Protima Rauwel, Charles H. Hervoches, Zuoan Li, Reidar Haugsrud
Source
Solid State Ionics
Volume: 261, Pages: 87-94
Time of Publication: 2014
Abstract Nominal Gd6WO12, Gd5.94Ca0.06WO12 − δ, Gd5.7Ca0.3WO12 − δ and Gd5.7WO12 − δ were synthesized by solid state reaction and wet chemistry methods. The structure and morphology of the materials were analyzed by XRD, SEM and TEM and the electrical conductivity was measured as a function of temperature in reducing and oxidizing atmospheres under wet and dry conditions. The total conductivity is essentially independent of composition above 700 C. Below 700 C, the conductivity of Ca-doped samples is higher than that of Gd6WO12 and Gd5.7WO12 − δ and increases with increasing doping concentration. The conductivity below 700 C is also higher under wet compared to dry conditions and, moreover, the H–D isotope effect on the conductivity is significant. Based on this, and on conductivity characterization as a function of pO2pO2 and pH2OpH2O, it was concluded that the materials are mixed ionic and electronic conductors where electrons and holes dominate at high temperatures and intermediate temperatures under sufficiently reducing and oxidizing conditions, respectively. Protons are the predominating ionic charge carriers below approximately 700 C. The hydrogen flux through Gd5.7Ca0.3WO12 − δ was measured as a function of temperature under wet and dry sweep gas conditions, as well as with varying pH2pH2 on the feed side, confirming the picture outlined by the conductivity measurements. A defect chemical model has been derived to which the conductivity data were fitted yielding thermodynamic and transport parameters describing the functional characteristics of the materials.
Keywords Proton; Structure; Gd6WO12; Ambipolar conductivity; Hydrogen flux
Remark Link

Solid Oxide-Molten Carbonate Nano-composite Fuel Cells: Particle Size Effect

Authors Shalima Shawuti, Mehmet A. Gulgun
Source
Journal of Power Sources
Time of Publication: 2014
Abstract Varying the amount of specific interface area in the CeO2-Na2CO3 nano-composite fuel cell electrolyte helped reveal the role of interfaces in ionic conductivity. We mixed ceria particles with micrometer or nanometer size distributions to obtain a specific surface area (SSA) in the composite from 47 m2/g to 203 m2/g. Micro-structural investigations of the nano-composite showed that the Na2CO3 phase serves as the glue in the microstructure, while thermal analysis revealed a glass transition-like behavior at 350 C. High SSA enhanced the ionic conductivity significantly at temperatures below 400 C. Moreover, the activation energy for the Arrhenius conductivity (σT) of the composites was lower than that of the Na2CO3 phase. This difference in the activation energies is consistent with the calculated dissociation energy of the carbonate phase. The strong dependence of conductivity on the SSA, along with differences in the activation energies, suggests that the oxide surface acted as a dissociation agent for the carbonate phase. A model for the solid composite electrolyte is proposed: in the nano-composite electrolyte, the oxide surface helps Na2CO3 dissociate, so that the "liberated" ions can move more easily in the interaction region around the oxide particles, thus giving rise to high ionic conductivities.
Keywords composite electrolyte; ionic conductivity; impedance spectroscopy; SOFC; interphase; activation energy
Remark in press, http://dx.doi.org/10.1016/j.jpowsour.2014.05.010
Link

Hydrogen permeation characteristics of La27Mo1.5W3.5O55.5

Authors Einar Vllestad, Camilla K. Vigen, Anna Magras, Reidar Haugsrud
Source
Journal of Membrane Science
Time of Publication: 2014
Abstract Hydrogen permeation in 30 % Mo-substituted lanthanum tungsten oxide membranes, La27Mo1.5W3.5O55.5 (LWMo), has been measured as a function of temperature, hydrogen partial pressure gradient, and water vapour pressure in the sweep gas. Transport of hydrogen by means of ambipolar proton-electron conductivity and – with wet sweep gas – water splitting contribute to the measured hydrogen content in the permeate. At 700 C under dry sweep conditions, the H2 permeability in LWMo was 610−4610−4 mL min−1 cm-1, which is significantly higher than for state-of-the-art SrCeO3-based membranes. Proton conductivity was identified as rate limiting for ambipolar bulk transport across the membrane. On these bases it is evident that Mo-substitution is a successful doping strategy to increase the n-type conductivity and H2 permeability compared to nominally unsubstituted lanthanum tungsten oxide. A steady-state model based on Wagner transport theory with partial conductivities as input parameters predicted H2 permeabilities in good agreement with the measured data. LWMo is a highly competitive mixed proton-electron conducting oxide for hydrogen transport membrane applications provided that long term stability can be ensured.
Remark Available online 14 March 2014
Link

Performance Variability and Degradation in Porous La1-xSrxCoO3-δ Electrodes

Authors Yunxiang Lu, Cortney R. Kreller, Stuart B. Adler, James R. Wilson, Scott A. Barnett, Peter W. Voorhees, Hsun-Yi Chen and Katsuyo Thornton
Source
J. of the Electrochemical Society
Volume: 161, Issue: 4, Pages: F561-F568
Time of Publication: 2014
Abstract Porous La1-xSrxCoO3-δ (LSC) electrodes with Sr composition x = 0.2 (LSC-82) and x = 0.4 (LSC-64) were prepared by screenprinting LSC powders onto rare-earth doped ceria electrolytes, followed by sintering at 950 ∼ 1100C, and characterization using scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) surface-area analysis, 3-D morphological imaging based on focused ion beam scanning electron microscopy (FIB-SEM), and energy dispersion X-ray spectroscopy (EDX/EDS). The batch-to-batch variability and degradation (over 1000 ∼ 2000 hours) of the electrochemical performance of these cells were studied using electrochemical impedance spectroscopy (EIS) and measurements of nonlinear electrochemical impedance (NLEIS). These measurements reveal a strong correlation between the characteristic frequency (ωc) and characteristic resistance (Rc) of the electrodes, which, when analyzed in light of microstructural data, indicates that performance variability and degradation are caused primarily by variations in the surface rate coefficient k(T) for O2 exchange.
Remark doi: 10.1149/2.101404jes
Link

Doped Germanate-Based Apatites as Electrolyte for Use in Solid Oxide Fuel Cells

Authors S.-F. Wang, Y.-F. Hsu, W.-J. Lin and K. Kobayashi
Source
Fuel Cells
Time of Publication: 2014
Abstract Apatite ceramics, known for their good electrical conductivities, have garnered substantial attention as an alternative electrolyte for solid oxide fuel cells (SOFCs). However, studies focusing on the electrochemical performances of SOFCs with apatities as electrolytes remain rare, partly due to their high sintering temperature. In this study, the effects of Mg2+, Al3+, Ga3+, and Sn4+ dopants on the characteristics of La9.5Ge6O26  δ are examined and their potential for use as SOFC electrolytes evaluated. The results indicate that La9.5Ge5.5Al0.5O26 is stabilized into a hexagonal structure, while the La9.5Ge5.5Sn0.5O26.25, La9.5Ge5.5Ga0.5O26, and La9.5Ge5.5Mg0.5O25.75 ceramics reveal triclinic cells accompanied with the second phase La2Sn2O7 or La2GeO5. The study further demonstrates that a high sintering temperature is needed for both the La9.5Ge5.5Mg0.5O25.75 and the La9.5Ge5.5Sn0.5O26.25 ceramics, and the worst electrical conductivity among the examined systems appears in the La9.5Ge5.5Ga0.5O26 ceramic. The La9.5Ge5.5Al0.5O26 ceramic is accordingly selected for cell evaluation due to its ability to reach densification at 1,350 C, its good electrical conductivity of 0.026 S cm–1 at 800 C, and its acceptable thermal expansion coefficient of 10.1  10–6 K–1. The maximum power densities of the NiO-SDC/La9.5Ge5.5Al0.5O26/LSCF-SDC single cell are found to be respectively 0.22, 0.16, 0.11, and 0.07 W cm–2 at 950, 900, 850, and 800 C.
Keywords Apatites; Cell Performance; Electrolyte; Impedance; Solid Oxide Fuel Cell
Remark Article first published online: 19 FEB 2014 DOI: 10.1002/fuce.201300093
Link

Effect of Nb substitution for Ti on the electrical properties of Yb2Ti2O7-based oxygen ion conductors

Authors L.G. Shcherbakova, J.C.C. Abrantes, D.A. Belov, E.A. Nesterova, O.K. Karyagina, A.V. Shlyakhtina
Source
Solid State Ionics
Time of Publication: 2014
Abstract We have studied the effect of niobium doping on the electrical conductivity of Yb2Ti2O7-based oxygen ion conductors. Yb2[Ti1 − xNbx]2O7 (x = 0.01, 0.04, 0.1) and (Yb0.8Tb0.1Ca0.1)2[Ti1 − xNbx]2O6.9 (x = 0; 0.05; 0.1) pyrochlore solid solutions were synthesized through coprecipitation followed by firing at 1550 C for 4 h. The materials were examined by XPS, XRD, scanning electron microscopy and impedance spectroscopy. Yb2(Ti0.99Nb0.01)2O7 was shown to have the highest oxygen ion conductivity in air (2.3 10− 3 S/cm at 750 C), which is however markedly lower than that of undoped Yb2Ti2O7. In the (Yb0.8Tb0.1Ca0.1)2[Ti1 − xNbx]2O6.9 (x = 0; 0.05; 0.1) system, the highest conductivity is offered by (Yb0.8Tb0.1Ca0.1)2[Ti0.95Nb0.05]2O6.9 (σ = 4.44 10− 3 S/cm at 650 C). Additional oxygen vacancies created by Ca doping in pyrochlore structure reduce the detrimental effect of Nb4 + doping on the oxide ion transport up to 5% Nb. The conductivity of the Yb2(Ti0.99Nb0.01)2O7 and (Yb0.8Tb0.1Ca0.1)2[Ti0.95Nb0.05]2O6.9 solid solutions was measured both in air and under reducing conditions (5% H2 in N2 and CO2 atmospheres). A comparative study of both these compositions under 5% H2 in N2 atmosphere showed that the transport mechanism was not affected by complex doping of the lanthanide and titanium sublattices in the Yb2Ti2O7-based materials and was related to oxygen vacancies. Conductivity measurements in CO2 were done to ensure correct evaluation of the ionic conductivity of (Yb0.8Tb0.1Ca0.1)2[Ti0.95Nb0.05]2O6.9, because in air it seems to be a mixed p-type and ionic conductor.
Keywords Oxide ion conductivity; Pyrochlore; Acceptor doping; Donor doping; Impedance spectroscopy
Remark Available online 1 February 2014; http://dx.doi.org/10.1016/j.ssi.2014.01.019
Link

Zr-doped samarium molybdates — potential mixed electron–proton conductors

Authors S.N. Savvin, A.V. Shlyakhtina, I.V. Kolbanev, A.V. Knotko, D.A. Belov, L.G. Shcherbakova, P. Nuez
Source
Solid State Ionics
Time of Publication: 2014
Abstract Two Zr-doped samarium molybdates View the MathML sourceSm6−x7Zrx7Mo17O127+x24−δ corresponding to x = 0.6 and 1 (SZMO) have been synthesized at 1600 C for 3 h using mechanically activated mixtures of starting oxides. Fluorite-like Sm0.771Zr0.086Mo0.143O1.739 − δ (06SZMO) and Sm0.714Zr0.143Mo0.143O1.756 − δ (10SZMO) have similar total conductivity of about 4 10− 4 S/cm at 800 C in air. Below 600 C, the total conductivity of 06SZMO in air exceeds that of 10SZMO. An increase in bulk and grain boundary conductivity of 06SZMO observed at low temperate under wet conditions suggests there may be a proton contribution to the total conductivity. Under reducing conditions (5% H2–Ar) 06SZMO becomes essentially an electronic conductor. Its conductivity reaches 0.25 S/cm at 800 C and the activation energy decreases to 0.3 eV.
Keywords Rare-earth; Sm molybdate; Fluorite; Oxide ion conductivity; Proton conductivity; Electron conductivity; Impedance spectroscopy
Remark Available online 6 February 2014; http://dx.doi.org/10.1016/j.ssi.2014.01.031
Link

Interstitial oxide ion conduction in (Sm2 − xZrx)Zr2O7 + δ

Authors A.V. Shlyakhtina, D.A. Belov, A.V. Knotko, I.V. Kolbanev, A.N. Streletskii
Source
Solid State Ionics
Time of Publication: 2014
Abstract The crystal structure and transport properties of (Sm2 − xZrx)Zr2O7 + x/2 (x = 0; 0.2; 0.32; 0.39; 0.48; 0.67; 0.78; 0.96; 1.14; 1.27) solid solutions have been investigated by X-ray techniques and impedance spectroscopy, respectively. The excess oxygen content of the composition with x = 0.2 has been determined by thermal analysis and mass spectrometry in a reducing atmosphere. The SmZrO system includes a two-phase (fluorite + pyrochlore) region for the (Sm2 − xZrx)Zr2O7 + x/2 (0.48 ≤ x < 0.96) solid solutions. The interstitial oxide ion conductivity of the (Sm2 − xZrx)Zr2O7 + x/2 (0.2 ≤ x < 0.48), 3 10− 3 S/cm at 750 C, is comparable to the vacancy-mediated conductivity of undoped Sm2Zr2O7. The bulk conductivity of the interstitial oxide ion conductors (Sm2 − xZrx)Zr2O7 + x/2 (0.2 ≤ x < 0.48) was shown to vary little in a wide range of Sm2O3 concentrations in contrast to the vacancy mediated oxide ion conductors Sm2(Zr2 − xSmx)O7 − δ (0 ≤ x < 0.29).
Remark Available online 2 February 2014; http://dx.doi.org/10.1016/j.ssi.2014.01.028
Link

Atmosphere controlled conductivity and Maxwell-Wagner relaxation in Bi0.5K0.5TiO3—BiFeO3 ceramics

Authors Morozov, Maxim I.; Einarsrud, Mari-Ann; Grande, Tor
Source
Journal of Applied Physics
Volume: 115, Issue: 4, Pages: 044104 - 044104-6
Time of Publication: 2014
Abstract Here, we report on a giant dielectric relaxation in (1 − x)Bi0.5K0.5TiO3—xBiFeO3 ceramics below ∼300 C, which becomes more pronounced with increasing BiFeO3 content. The relaxation was shown to be of Maxwell-Wagner type and associated with charge depletion at the electroded interfaces. It was also shown that the relaxation could be controlled or, eventually, removed by heat treatment in controlled partial pressure of oxygen. This was rationalized by the relationship between the electrical conductivity and variation in the oxidation state of Fe, which is strongly coupled to the partial pressure of oxygen. The results are discussed with emphasis on oxygen diffusion and point defect equilibria involving oxygen vacancies and iron in divalent and tetravalent state. Finally, the barrier-free dielectric properties of the (1 − x)Bi0.5K0.5TiO3—xBiFeO3 ceramics are reported.
Remark Link

Atmosphere controlled conductivity and Maxwell-Wagner relaxation in Bi0.5K0.5TiO3—BiFeO3 ceramics

Authors Maxim I. Morozov, Mari-Ann Einarsrud and Tor Grande
Source
J. Appl. Phys.
Volume: 115, Pages: 044104
Time of Publication: 2014
Abstract Here, we report on a giant dielectric relaxation in (1 − x)Bi0.5K0.5TiO3 — xBiFeO3 ceramics below ∼300 C, which becomes more pronounced with increasing BiFeO3 content. The relaxation was shown to be of Maxwell-Wagner type and associated with charge depletion at the electroded interfaces. It was also shown that the relaxation could be controlled or, eventually, removed by heat treatment in controlled partial pressure of oxygen. This was rationalized by the relationship between the electrical conductivity and variation in the oxidation state of Fe, which is strongly coupled to the partial pressure of oxygen. The results are discussed with emphasis on oxygen diffusion and point defect equilibria involving oxygen vacancies and iron in divalent and tetravalent state. Finally, the barrier-free dielectric properties of the (1 − x)Bi0.5K0.5TiO3 — xBiFeO3 ceramics are reported.
Remark Link

Characterisation of structure and conductivity of BaTi0.5Sc0.5O3 − δ

Authors S.M.H. Rahman, I. Ahmed, R. Haugsrud, S.G. Eriksson, C.S. Knee
Source
Solid State Ionics
Volume: 225, Pages: 140–146
Time of Publication: 2014
Abstract BaTi0.5Sc0.5O3 − δ was prepared via solid state reaction route and final sintering at 1550 C. High resolution X-ray powder diffraction on the as-prepared material reveals a cubic perovskite structure with a unit cell parameter, a = 4.1343(1) . Thermogravimetric analysis revealed the presence of significant levels of protons in the as-prepared material and 74% of the theoretically achievable protonation through filling of oxide ion vacancies was attained on exposure to a humid environment at 185 C. Infrared spectroscopy revealed a broad Osingle bondH stretching band confirming the presence of OHO• defects. Electrical conductivity was measured with variable frequency AC impedance methods in oxygen, argon, and hydrogen under dry, hydrated (H2O) and heavy water (D2O) conditions. In the temperature range of 150–550 C in a wet gas atmosphere the conductivity is significantly higher than that observed for dry conditions, indicating that protons are the dominant charge carriers. Conductivity is also found to be higher in dry oxygen in comparison with dry argon over the whole temperature range of 150–1000 C, characteristic of contribution from p-type charge carriers under oxidising atmospheres. At 550 C the proton conductivity was estimated to be 2.89 10− 4 S cm− 1 in wet Ar. Fitting of conductivity data provides a hydration enthalpy change (ΔHhydr0) of − 100 5 kJ/mol and hydration entropy change (ΔShydr0) of − 160 10 J/mol K.
Keywords Barium titanate; BaTiO3; Perovskite; Proton conductivity; X-ray diffraction; Hydration
Remark Link

Stability of La-Sr-Co-Fe Oxide-Carbonate Dual-Phase Membranes for Carbon Dioxide Separation at High Temperatures

Authors Tyler Norton , Jose Ortiz-Landeros , and Jerry Y.S. Lin
Source
Ind. Eng. Chem. Res.
Time of Publication: 2014
Abstract Dual-phase membranes consisting of a mixed ionic and an electronic conducting ceramic phase and an ionically conductive molten carbonate phase have the ability to selectively separate CO2 at high temperature with or without the presence of O2. This study examines the stability of a dual-phase ceramic-carbonate membrane consisting of La0.6Sr0.4Co0.8Fe0.2O3-δ (LSCF) and an eutectic molten carbonate phase composed of Li2CO3, Na2CO3, and K2CO3. LSCF-carbonate membranes exposed to a CO2/He gradient at temperatures between 800-900oC result in a drastic decrease in CO2 permeation before reaching steady-state after more than 60 hours of exposure to the permeating gases due to surface reaction between CO2 and the LSCF ceramic phase of the membrane, resulting in decomposition of the membrane surface. The introduction of O2 in the feed gas, however, helps maintain the LSCF ceramic phase structure and results in stable CO2 permeation flux at much higher value due to a change in transport mechanism in the membrane. The results suggest finding oxygen ionic or mixed-conducting ceramic material stable in CO2 for the dual-phase membrane is critical to ensure stability of the membrane for CO2 permeation.
Remark DOI: 10.1021/ie4033523
Link

Synthesis and characterization of the micro-mesoporous anode materials and testing of the medium temperature solid oxide fuel cell single cells

Author Kadi Tamm
Source
Time of Publication: 2013
Remark Dissertation
Link

Polymorphism and properties of Bi2WO6 doped with pentavalent antimony

Authors E.P. Kharitonova, D.A. Belov, A.B. Gagor, A.P. Pietraszko, O.A. Alekseeva, V.I. Voronkova
Source
Journal of Alloys and Compounds
Time of Publication: 2014
Abstract Antimony-containing solid solutions isostructural with bismuth tungstate, Bi2WO6, have been prepared in air as polycrystalline samples by solid-state reactions and as single crystals by unseeded flux growth. The antimony in the solid solutions is in a pentavalent state and substitutes for tungsten in the structure of Bi2WO6. The Bi2W1–xSbxO6–y solid solutions have been shown to exist in the composition range 0 ⩽ x ⩽ 0.05. We have examined the effect of Sb5+ doping on the polymorphism and properties of Bi2WO6. In contrast to undoped Bi2WO6, antimony-substituted bismuth tungstate does not completely transform into its high-temperature, monoclinic phase at 960 C and remains two-phase up to temperatures approaching its melting point. Antimony substitution for tungsten has a weak effect on the temperatures of the ferroelectric phase transitions. Heterovalent substitution of Sb5+ for W6+ is accompanied by the formation of extra oxygen vacancies and an increase in the electrical conductivity of the solid solutions by one to two orders of magnitude relative to undoped Bi2WO6.
Keywords Aurivillius phases; Bi2WO6; Ceramics; Phase transitions; Electrophysical properties; Differential scanning calorimetry
Remark Available online 3 January 2014
Link

Effect of Ni Concentration on Phase Stability, Microstructure and Electrical Properties of BaCe0.8Y0.2O3-δ - Ni Cermet SOFC Anode and its application in proton conducting ITSOFC

Authors Pooja Sawant, S. Varma, M.R. Gonal, B.N. Wani, Deep Prakash, S.R. Bharadwaj
Source
Electrochimica Acta
Time of Publication: 2013
Abstract In this work we have studied the effect of Ni concentration on phase stability, microstructure and electrical properties of BaCe0.8Y0.2O3-δ (BCY)-Ni cermet SOFC anode. It has been seen that Ni forms composite with BCY without forming any solid solution in both oxidized and reduced state. Also, microstructural analysis reveals the effect of Ni on porosity and triple phase boundaries necessary for electrochemical reactions during cell operation. Electrical conductivity values obtained from dc four probe technique in H2 atmosphere increase with an increase in Ni content. Composites with low vol% of Ni contents i.e. 19% (Ni19) and 26% (Ni26) show predominantly semiconductor-like behaviour whereas higher vol% viz. 35% (Ni35), 45% (Ni45) and 56% (Ni56) composites show electronic conductivity behaviour. This confirms that electronic conduction occurs through metallic Ni phase. Also, anode supported single cell for proton conducting SOFC has been fabricated using Ni35 composition and its current-potential characteristics measured at different temperatures.
Keywords Cermet; X-ray diffraction; Electrical conductivity; Four probe; Single Cell
Remark Available online 25 December 2013
Link

Cathode compatibility, operation, and stability of LaNbO4-based proton conducting fuel cells

Authors Anna Magras, Marie-Laure Fontaine, Rune Bredesen, Reidar Haugsrud, Truls Norby
Source
Solid State Ionics
Time of Publication: 2013
Abstract Cathodes compatible with Ca-doped LaNbO4 (LCNO) and the operation of a complete proton conducting fuel cell based on this electrolyte are presented. The best performing cathode was a 50 vol.% La0.8Sr0.2MnO3 (LSM)–50 vol.% LCNO composite, with an overall area specific resistance (ASR) of ~ 10 Ω cm2 at 800 C in wet air. Pt and La0.8Sr0.2(Cr0.5Mn0.5)O3-based cathodes exhibit higher ASRs. The performance of a complete Ni–LCNO//LCNO//LSM–LCNO fuel cell shows a high open circuit voltage but with relatively low performance, in agreement with the modest proton conductivity of LaNbO4-based materials and cathode performances. The cell exhibits stable operation with CO2 containing atmosphere on the cathode side, confirming the chemical robustness of LaNbO4-based electrolytes.
Keywords Proton conducting fuel cells; Manufacturing; Impedance spectroscopy; LaNbO4; Characterization; Cathode performance
Remark Available online 22 December 2013;
Link

Determination of Oxygen Diffusion Coefficients in La1-xSrxFe1-yGayO3-δ Perovskites Using Oxygen Semi-Permeation and Conductivity Relaxation Methods

Authors P. M. Geffroy, Y. Hu, A. Vivet, T. Chartier and G. Dezanneau
Source
Journal of the Electrochemical Society
Volume: 161, Issue: 3, Pages: F153-F160
Time of Publication: 2014
Abstract This paper reports new evidence that oxygen surface exchange and bulk diffusion in a mixed conductor can be simultaneously determined via the oxygen semi-permeation method. Herein, we report the use of an original apparatus for oxygen activity measurements at both membrane surfaces to evaluate the oxygen surface exchange and bulk diffusion coefficients. Oxygen surface exchange and bulk diffusion in the La1-xSrxFe1-yGayO3-δ perovskite series are also determined and compared with the results from three different methods: isotopic exchange, conductivity relaxation, and oxygen semi-permeation. Although the thermodynamic conditions for these methods are not exactly the same, the values obtained for the oxygen surface exchange and bulk diffusion coefficients are in good agreement.
Remark Link

Entwicklung protonenleitender Werkstoffe und Membranen auf Basis von Lanthan-Wolframat fr die Wasserstoffabtrennung aus Gasgemischen

Author J Seeger
Source
Book of its own
Time of Publication: 2013
Remark Link

Porous La 0.6 Sr 0.4 CoO 3-δ thin film cathodes for large area micro solid oxide fuel cell MEMS power generators

Authors I. Garbayo, V. Esposito, S. Sanna, A. Morata, D. Pla, L. Fonseca, N. Sabat, A. Tarancn
Source
Journal of Power Sources
Time of Publication: 2013
Abstract Porous La0.6Sr0.4CoO3-δ thin films were fabricated by pulsed laser deposition for being used as a cathode for micro solid oxide fuel cell applications as MEMS power generators. Symmetrical La0.6Sr0.4CoO3-δ/yttria-stabilized zirconia/La0.6Sr0.4CoO3-δ free-standing membranes were fabricated using silicon as a substrate. A novel large-area membrane design based on grids of doped-silicon slabs. Thermo-mechanical stability of the tri-layer membranes was ensured in the intermediate range of temperatures up to 700C. In-plane conductivity of ca. 300 S/cm was measured for the cathode within the whole range of application temperatures. Finally, area specific resistance values below 0.3 Ωcm2 were measured for the cathode/electrolyte bi-layer at 700C in the exact final micro solid oxide fuel cell device configuration, thus presenting La0.6Sr0.4CoO3-δ as a good alternative for fabricating reliable micro solid oxide fuel cells for intermediate temperature applications.
Keywords Micro Solid Oxide Fuel Cell, thin film cathode, self-supported electrolyte
Remark DOI: 10.1016/j.jpowsour.2013.10.038

Nanocrystalline Sm0.5Sr0.5CoO3−δ synthesized using a chelating route for use in IT-SOFC cathodes: microstructure, surface chemistry and electrical conductivity

Authors Rares Scurtu, Simona Somacescu, Jose Maria Calderon-Moreno, Daniela Culita, Ion Bulimestru, Nelea Popa, Aurelian Gulea, Petre Osiceanu
Source
Journal of Solid State Chemistry
Time of Publication: 2013
Abstract Nanocrystalline Sm0.5Sr0.5CoO3−δ powders were synthesized by a chelating route using different polyfunctional HxAPC acids (APC=aminopolycarboxylate; x= 3, 4, 5). Different homologous aminopolycarboxylic acids, namely nitrilotriacetic (H3nta), ethylenediaminetetraacetic (H4edta), 1,2-cyclohexanediaminetetracetic (H4cdta) and diethylenetriaminepentaacetic (H5dtpa) acid, were used as chelating agents to combine Sm, Sr, Co elements into a perovskite structure. The effects of the chelating agents on the crystalline structure, porosity, surface chemistry and electrical properties were investigated. The electrical properties of the perovskite-type materials emphasized that their conductivities in the temperature range of interest (600–800 C) depend on the nature of the precursors as well as on the presence of a residual Co oxide phase as shown by XRD and XPS analysis. The surface chemistry and the surface stoichiometries were determined by XPS revealing a complex chemical behavior of Sr that exhibits a peculiar „surface phase” and „bulk phase” chemistry within the detected volume (<10 nm).
Keywords Cathode; Perovkites; Electrical Conductivity; XPS; IT-SOFC
Remark Available online 5 November 2013
Link

Effects of temperature, triazole and hot-pressing on the performance of TiO2 photoanode in a solid-state photoelectrochemical cell

Authors Kingsley O. Iwu, Augustinas Galeckas, Spyros Diplas, Frode Seland, Andrej Yu. Kuznetsov,Truls Norby
Source
Electrochimica Acta
Time of Publication: 2013
Abstract The photocurrent of hydrogen generating solid-state photoelectrochemical cell utilising a polybenzimidazole proton-conducting membrane and gaseous anode reactants has been enhanced by operation at higher temperatures. With a bias of 0 V for example, photocurrent increased from 15 to 30 μA/cm2 on moving from 25 C to 45 C. The increase in photocurrent, which was limited by the dehydration of the cell, was shown to have contribution from improved electrode kinetics. Modification of TiO2 surface with triazole, a conjugated heterocyclic compound, led to significant increase in photocurrent - up to 4 fold increase at 0 V and 25 C. This was attributed to improved separation of photogenerated charge carriers, as confirmed by correspondingly increased carrier lifetimes from 50 ns to 90 ns for triazole-modified TiO2. Assembly of the photoelectrochemical cell by hot-pressing induced a ̴ 0.3 eV red shift in optical absorption edge of TiO2, in agreement with a shift of its valence band maximum to higher binding energy.
Keywords Solid-state; photoelectrochemical; XPS; carrier lifetime; triazole
Remark Available online 28 October 2013
Link

Synthesis and Investigation of Porous Ni–Al Substrates for SolidOxide Fuel Cells

Authors A. A. Solov’ev, N. S. Sochugov , I. V. Ionov , A. I. Kirdyashkin , V. D. Kitler , A. S. Maznoi , Yu. M. Maksimov , and T. I. Sigfusson
Source
Materials of power engineering and radiationresistant materials
Time of Publication: 2013-10
Abstract Selfpropagating hightemperature synthesis (SHS) is applied for the production of porous supporting Ni–Al bases of solidoxide fuel cells. The effect of synthesis onditions and the composition of source powders on the phase composition, microstructure, gas permeability, corrosion resistance, and other proper ties of obtained Ni–Al samples is investigated. The possibility is shown for the formation of solidoxide fuel cells (SOFCs) on the surface of porous Ni–Al plates. The cells have the structure Ni–ZrO3:Y2O3 anode/ZrO3:Y2O3 electrolyte/La0.8Mn0.2SrO3 cathode and provide a specific power of 400 mW/cm2 at a temperature of 800C.
Keywords selfpropagating hightemperature synthesis, Ni–Al, solidoxide fuel cells, ZrO3:Y2O3 electrolyte, magnetron sputtering.
Remark Link

Galliosilicate glasses for viscous sealants in solid oxide fuel cell stacks: Part III: Behavior in air and humidified hydrogen

Authors T. Jin, M.O. Naylor, J.E. Shelby, S.T. Misture
Source
International Journal of Hydrogen Energy
Time of Publication: 2013
Abstract Optimized boro-galliosilicate glasses were selected to evaluate their viscous sealing performance in both air and humidified hydrogen atmospheres. Selected low-alkali and alkali-free glasses show excellent performance, with viscous behavior maintained for more than 1000 h in wet hydrogen. Candidate sealants were thermally treated at 850 and 750 C for up to 1000 h in contact with alumina coated 441 stainless steel (Al-SS) and 8 mol% yttria-stabilized zirconia (8YSZ). Each sealant crystallizes appreciably by 1000 h, and their coefficients of thermal expansion range from 10.2 to 11.7 10−6 K−1, 100–400 C. The remnant amorphous phases in most of the partially crystallized sealants show softening points near or below the target operating temperatures, thus enabling viscous sealing. Humidified hydrogen in general increases the rate of crystallization but does not change the crystalline phases formed or interactions with 8YSZ. For the low-alkali GaBA series, wet H2 enhances the interfacial interaction between potassium in the glass phase and the protective alumina coating on the stainless steel.
Keywords Solid oxide fuel cell; Sealing glass; Galliosilicate; Thermal expansion; Hydrogen
Remark Available online 25 October 2013
Link

Porous La0.6Sr0.4CoO3-δ thin film cathodes for large area micro solid oxide fuel cell MEMS power generators

Authors I. Garbayo, V. Esposito, S. Sanna, A. Morata, D. Pla, L. Fonseca, N. Sabat, A. Tarancn
Source
Journal of Power Sources
Time of Publication: 2013
Abstract Porous La0.6Sr0.4CoO3-δ thin films were fabricated by pulsed laser deposition for being used as a cathode for micro solid oxide fuel cell applications as MEMS power generators. Symmetrical La0.6Sr0.4CoO3-δ/yttria-stabilized zirconia/La0.6Sr0.4CoO3-δ free-standing membranes were fabricated using silicon as a substrate. A novel large-area membrane design based on grids of doped-silicon slabs. Thermo-mechanical stability of the tri-layer membranes was ensured in the intermediate range of temperatures up to 700C. In-plane conductivity of ca. 300 S/cm was measured for the cathode within the whole range of application temperatures. Finally, area specific resistance values below 0.3 Ωcm2 were measured for the cathode/electrolyte bi-layer at 700C in the exact final micro solid oxide fuel cell device configuration, thus presenting La0.6Sr0.4CoO3-δ as a good alternative for fabricating reliable micro solid oxide fuel cells for intermediate temperature applications.
Remark Available online 18 October 2013
Link

Nano Coated Interconnects for SOFC (NaCoSOFC)

Authors Jan Froitzheim, Anna Magraso, Tobias Holt, Mats W Lundberg, Hannes Falk Windisch, Robert Berger, Rakshith Nugehalli Sachitanand, Jrgen Westlinder, Jan-Erik Svensson and Reidar Haugsrud
Source
ECS Transactions
Volume: 57, Issue: 1, Pages: 2187-2193
Time of Publication: 2013
Abstract The NaCoSOFC project is focused on the development of nano coatings for SOFC interconnects. The project is sponsored by the Nordic Top Level Research Initiative and has four project partners: Sandvik Materials Technology which is producing coated interconnects, Chalmers University of Technology and the University of Oslo that characterize samples with respect to e.g. corrosion, Cr evaporation and ASR as well as Topsoe Fuel Cell that is testing the developed interconnects in its stacks. The developed coatings are based on a combination of Co with RE elements and exhibit high corrosion resistance, 10 fold decrease in Cr evaporation and ASR values that are approximately 50% of the uncoated material.
Remark Link

Nano Coated Interconnects for SOFC (NaCoSOFC)

Source
Time of Publication: 2013

Application of FIB-TOF-SIMS and FIB-SEM-EDX Methods for the Analysis of Element Mobility in Solid Oxide Fuel Cells

Authors Rait Kanarbik, Priit Mller, Indrek Kivi and Enn Lust
Source
ECS Transactions
Volume: 57, Issue: 1, Pages: 581-587
Time of Publication: 2013
Abstract The solid oxide fuel cell single cells with porous Pr0.6Sr0.4CoO3-δ and La0.6Sr0.4CoO3-δ (PSCO, LSCO respectively) cathodes on compact Ce0.9Gd0.1O2-δ|Zr0.85Y0.15O2-δ or Ce0.9Gd0.1O2-δ|Zr0.85Sc0.15O2-δ bi-layered electrolytes deposited onto Ni-Zr0.85Y0.15O2-δ (Ni-ZYO) or Ni- Ce0.9Gd0.1O2-δ (Ni-CGO) supporting anode were prepared for ion (element) mobility studies. Focused ion beam - time of flight - secondary ion mass spectrometry (FIB-TOF-SIMS) method in addition to FIB-SEM, SEM-EDX and XRD methods has been used for analysis of mass-transfer (interlayer diffusion) of cathode electrode elements, demonstrating that during PSCO and LSCO sintering at 1100C on to CGO|ZYO or CGO|ZScO bilayered electrolyte, noticeable mass-transfer of Sr2+ cations through the partially microporous CGO has been verified using FIB-TOF-SIMS and SEM-EDX methods. The single cells have been additionally studied using cyclic voltammetry, electrochemical impedance and chronoamperometry methods and high power densities have been demonstrated.
Remark Link

Chromium Poisoning of La2NiO4+δ Cathodes

Authors Soo-Na Lee, Alan Atkinson and John A. Kilner
Source
ECS Transactions
Volume: 57, Issue: 1, Pages: 605-613
Time of Publication: 2013
Abstract It has been reported that Sr-containing materials (such as LSCF) are susceptible to Cr-poisoning by the formation of SrCrO4 and therefore there is interest in Sr-free cathodes such as La2NiO4+δ (LNO). In this study, La2NiO4+δ electrodes were deposited symmetrically onto Ce0.9Gd0.1O1.95 electrolytes by screen printing. The LNO electrodes were solution impregnated with targeted amounts of chromium and then characterised by impedance spectroscopy (520- 800C). XRD of LNO/Cr2O3 powder mixtures annealed at 900C showed that there is a reaction between them. Nevertheless, the impedance results indicate that LNO is less prone to chromium deactivation than LSCF.
Remark Link

Effect of Steam-to-Carbon Ratio on Degradation of Ni-YSZ Anode Supported Cells

Authors Hossein Madi, Stefan Diethelm, Jan Van herle and Nathalie Petigny
Source
ECS Transaction
Volume: 57, Issue: 1, Pages: 1517-1525
Time of Publication: 2013
Abstract Internal steam reforming (IR) of methane was investigated on Ni-YSZ anode supported cells, looking in particular at the effect of the steam to carbon (S/C) ratio on the degradation rate. The cells were fed with different H2O/CH4 mixtures during 100 hours sequences, alternating with sequences of dry H2 feeding. V-I characterization was performed before and after each sequence, and EIS measurements were performed regularly. A marked degradation was observed during the IR sequences while it was negligible under dry H2 feed. The observed degradation, attributed to carbon deposition on the anode active sites, was partially reversible for S/C >1.5, whereas it became irreversible at lower S/C.
Remark Link

Synthesis, properties and phase transitions of pyrochlore- and fluorite-like Ln2RMO7 (Ln=Sm, Ho; R=Lu, Sc; M= Nb, Ta)

Authors A.V. Shlyakhtina, D.A. Belov, K.S. Pigalskiy, A.N. Shchegolikhin, I.V. Kolbanev, O.K. Karyagina
Source
Materials Research Bulletin
Time of Publication: 2013
Abstract We have studied the new compounds with fluorite-like (Ho2RNbO7 (R = Lu, Sc)) and pyrochlore-like (Sm2ScTaO7) structure as potential oxide ion conductors. The phase formation process (from 1200 to 1600 C) and physical properties (electrical, thermo mechanical, and magnetic) for these compounds were investigated. Among the niobate materials the highest bulk conductivity is offered by the fluorite-like Ho2ScNbO7 synthesized at 1600 C: 3.8 10−5 S/cm at 750 C, whereas in Sm system the highest bulk conductivity, 7.3 10−6 S/cm at 750 C, is offered by the pyrochlore Sm2ScTaO7 synthesized at 1400 C. In Sm2ScTaO7 pyrochlore we have observed the first-order phase transformation at ∼650–700 C is related to rearrangement process in the oxygen sublattice of the pyrochlore structure containing B-site cations in different valence state and actually is absent in the defect fluorites. The two holmium niobates show Curie–Weiss paramagnetic behavior, with the prevalence of antiferromagnetic coupling. The magnetic susceptibility of Sm2ScTaO7 is a weak function of temperature, corresponding to Van Vleck paramagnetism.
Keywords Pyrochlore; Fluorite; Phase transition; Ionic conductivity; Thermo mechanical analysis; Dielectric permittivity; Loss tangent; Magnetic susceptibility
Remark Available online 11 October 2013
Link

Proton Conductivity in Solid Solution 0.7(CaWO4)–0.3(La0.99Ca0.01NbO4) and Ca(1−x)LaxW(1−y)TayO4

Authors Camilla K. Vigen, Reidar Haugsrud
Source
Journal of the American Ceramic Society
Time of Publication: 2013
Abstract The conductivity of nominal CaWO4, CaW0.99Ta0.01O4–δ, 0.7(CaWO4)–0.3(La0.99Ca0.01NbO4–δ), and Ca0.9La0.1WO4+δ has been studied by means of a.c. impedance measurements. Proton conductivity was observed for CaW0.99Ta0.01O4–δ, which displayed exothermic hydration with enthalpy and entropy of –82 kJ/mol and –120 J/molK, respectively. The proton mobility in CaW0.99Ta0.01O4–δ was low, with enthalpy and preexponential factor of mobility of 82 kJ/mol and 0.7 cm2K/Vs. The high enthalpy of mobility is interpreted to reflect association between the acceptor dopant and protonic defects, whereas the low preexponential factor of mobility may reflect a lower proton concentration than assumed. Rietveld refinement indicated low solubilities of La on Ca-site and Ta on W-site. Proton conductivity was also observed in undoped CaWO4, however, not in Ca0.9La0.1WO4+δ. The conductivity of 0.7(CaWO4)–0.3(La0.99Ca0.01NbO4–δ) behaved much like that of undoped LaNbO4, likely due to a very low acceptor dopant concentration.
Remark Article first published online: 1 OCT 2013. DOI: 10.1111/jace.12587
Link

The Investigation of E-beam Deposited Titanium Dioxide and Calcium Titanate Thin Films

Authors Kristina BOČKUTĖ, Giedrius LAUKAITIS, Darius VIRBUKAS, Darius MILČIUS
Source
MATERIALS SCIENCE (MEDIAGOTYRA)
Volume: 19, Issue: 3, Pages: 245-249
Time of Publication: 2013
Abstract Thin titanium dioxide and calcium titanate films were deposited using electron beam evaporation technique. The substrate temperature during the deposition was changed from room temperature to 600 C to test its influence on TiO2 film formation and optical properties. The properties of CaTiO3 were investigated also. For the evaluation of the structural properties the formed thin ceramic films were studied by X-ray diffraction (XRD), energy dispersive spectrometry (EDS), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Optical properties of thin TiO2 ceramics were investigated using optical spectroscope and the experimental data were collected in the ultraviolet-visible and near-infrared ranges with a step width of 1 nm. Electrical properties were investigated by impedance spectroscopy.It was found that substrate temperature has influence on the formed thin films density. The density increased when the substrate temperature increased. Substrate temperature had influence on the crystallographic, structural and optical properties also.
Keywords electron beam evaporation; titanium oxide; calcium titanate; optical properties
Remark DOI: http://dx.doi.org/10.5755/j01.ms.19.3.1805
Link

Synthesis and Characterization of Nonsubstituted and Substituted Proton-Conducting La6–xWO12–y

Authors Janka Seeger, Mariya E. Ivanova, Wilhelm A. Meulenberg, Doris Sebold, Detlev Stver, Tobias Scherb, Gerhard Schumacher, Sonia Escolstico, Cecilia Sols, and Jos M. Serra
Source
Inorganic Chemistry
Publisher: ACS Publications, Time of Publication: 2013
Abstract Mixed proton–electron conductors (MPEC) can be used as gas separation membranes to extract hydrogen from a gas stream, for example, in a power plant. From the different MPEC, the ceramic material lanthanum tungstate presents an important mixed protonic–electronic conductivity. Lanthanum tungstate La6–xWO12–y (with y = 1.5x + δ and x = 0.5–0.8) compounds were prepared with La/W ratios between 4.8 and 6.0 and sintered at temperatures between 1300 and 1500 C in order to study the dependence of the single-phase formation region on the La/W ratio and temperature. Furthermore, compounds substituted in the La or W position were prepared. Ce, Nd, Tb, and Y were used for partial substitution at the La site, while Ir, Re, and Mo were applied for W substitution. All substituents were applied in different concentrations. The electrical conductivity of nonsubstituted La6–xWO12–y and for all substituted La6–xWO12–y compounds was measured in the temperature range of 400–900 C in wet (2.5% H2O) and dry mixtures of 4% H2 in Ar. The greatest improvement in the electrical characteristics was found in the case of 20 mol % substitution with both Re and Mo. After treatment in 100% H2 at 800 C, the compounds remained unchanged as confirmed with XRD, Raman, and SEM.
Keywords ProGasMix
Remark lanthanum tungstate
La6–xWO12–y
Link

Synthesis and Characterization of Nonsubstituted and Substituted Proton-Conducting La6–xWO12–y

Authors Janka Seeger, Mariya E. Ivanova, Wilhelm A. Meulenberg, Doris Sebold, Detlev Stver, Tobias Scherb, Gerhard Schumacher, Sonia Escolstico, Cecilia Sols, and Jos M. Serra
Source
Inorg. Chem.
Time of Publication: 2013
Abstract Mixed proton–electron conductors (MPEC) can be used as gas separation membranes to extract hydrogen from a gas stream, for example, in a power plant. From the different MPEC, the ceramic material lanthanum tungstate presents an important mixed protonic–electronic conductivity. Lanthanum tungstate La6–xWO12–y (with y = 1.5x + δ and x = 0.5–0.8) compounds were prepared with La/W ratios between 4.8 and 6.0 and sintered at temperatures between 1300 and 1500 C in order to study the dependence of the single-phase formation region on the La/W ratio and temperature. Furthermore, compounds substituted in the La or W position were prepared. Ce, Nd, Tb, and Y were used for partial substitution at the La site, while Ir, Re, and Mo were applied for W substitution. All substituents were applied in different concentrations. The electrical conductivity of nonsubstituted La6–xWO12–y and for all substituted La6–xWO12–y compounds was measured in the temperature range of 400–900 C in wet (2.5% H2O) and dry mixtures of 4% H2 in Ar. The greatest improvement in the electrical characteristics was found in the case of 20 mol % substitution with both Re and Mo. After treatment in 100% H2 at 800 C, the compounds remained unchanged as confirmed with XRD, Raman, and SEM.
Remark DOI: 10.1021/ic401104m; Publication Date (Web): September 3, 2013
Link

Defects and Transport Properties in TiNb2O7

Authors Wen Xing, Liv-Elisif Kalland, Zuoan Li, Reidar Haugsrud
Source
Journal of the American Ceramic Society
Time of Publication: 2013
Abstract The electrical conductivity of TiNb2O7 was characterized as a function of temperature, inline image and inline image. The total conductivity was independent of inline image in the low oxygen partial pressure regime, while a dependency of inline image was observed at higher oxygen partial pressures. The conductivity increased with increasing inline image under oxidizing conditions below 700C. Mixed electronic and protonic conduction was indicated by H/D isotope exchange and transport number measurements. A defect model based on interstitial type of hydration was established and fitted to the conductivity data allowing for determination of physicochemical parameters of hydration and electron migration.
Remark Article first published online. DOI: 10.1111/jace.12558
Link

CO2 removal at high temperature from multi-component gas stream using porous ceramic membranes infiltrated with molten carbonates

Authors M.-L. Fontaine, T.A. Peters, M.T.P. McCann, I. Kumakiri, R. Bredesen
Source
Energy Procedia
Volume: 37, Pages: 941–951
Time of Publication: 2013-09
Abstract This work reports on the investigation of CO2 selective membranes for pre-combustion and post- combustion processes, in which CO2 is extracted from multi-component gas streams at intermediate temperature (400 – 600 C). The dual-phase membranes developed in this work are designed as a porous oxide ion conducting ceramic matrix, which is infiltrated with a molten carbonate phase. Both ex-situ and in-situ characterization methods were used to study disk shaped and tubular membranes. The gas transport properties of disk-shaped membranes were further investigated under various operating conditions relevant for both post-combustion and pre-combustion applications.
Keywords Membrane; CO2 separation; molten carbonate; dual-phase membrane; ionic conductor
Remark Link

Preparation and electrical properties of Li–Si–Al–O–N ceramics

Authors Eiichirou Narimatsu∗, Takashi Takeda, Toshiyuki Nishimura, Naoto Hirosaki
Source
Journal of Asian Ceramic Societies
Volume: 1, Pages: 191–196
Time of Publication: 2013
Abstract Ceramic samples were synthesized by hot pressing mixtures of Li3N, Si3N4, AlN, Al2O3, and Li2CO3withnominal compositions of LiSi2−xAlxOxN3−x(x = 0–0.75) at 20 MPa and 1773–2073 K in a N2atmosphere of0.10 MPa. The samples prepared with nominal compositions, x = 0.25 and 0.50, showed electronic con-ductivities of 2.2 and 4.2 S m−1at room temperature with activation energies of 3.8 and 3.9 kJ mol−1,respectively. Electronic conductive parts were detected in the sample of x = 0.50 by conductive atomicforce microscopy (AFM). In this sample, a glassy thin layer, having a Si/Al atomic ratio of 3.8, was observedbetween the grains of LiSi2−xAlxOxN3−xsolid solution by high-resolution transmission electron microscopy(HRTEM). It was expected that the glassy phase of grain boundaries is an electronic conductive pathwaybesides the conductive parts observed by AFM.

Effects of Nb5+, Mo6+, and W6+ dopants on the germanate-based apatites as electrolyte for use in solid oxide fuel cells

Authors Sea-Fue Wang, Yung-Fu Hsu, Wan-Ju Lin
Source
International Journal of Hydrogen Energy
Volume: 38, Issue: 27, Pages: 12015–12023
Time of Publication: 2013-09
Abstract Rare information is available in the literature on the cell performance of the solid oxide fuel cells (SOFCs) using apatites known for their good electrical conductivity as electrolyte materials. In this study, La9.5Ge5.5Nb0.5O26.5, La9.5Ge5.5Mo0.5O26.75, and La9.5Ge5.5W0.5O26.75 ceramics were prepared and characterized. The results indicated that the La9.5Ge5.5Nb0.5O26.5 and La9.5Ge5.5W0.5O26.75 ceramics reported hexagonal phase, while the La9.5Ge5.5Mo0.5O26.75 ceramic demonstrated triclinic symmetry. Among the apatities evaluated, La9.5Ge5.5Nb0.5O26.5 sintered at 1450 C showed the best conduction with an electrical conductivity value of 0.045 S/cm at 800 C. Button cells of NiO–SDC/La9.5Ge5.5Nb0.5O26.5/LSCF–SDC were built and revealed good structural integrity. The total ohmic resistance (R0) and interfacial polarization resistance (RP) of the cell read 0.428 and 0.174 Ω cm2 and 0.871 and 1.164 Ω cm2, respectively at 950 and 800 C. The maximum power densities (MPD) of the single cell at 950 and 800 C were respectively 0.363 and 0.095 W cm−2. Without optimizing the anode and cathode as well as hermetic sealing of the cell against the gas, the study found the performance of the single cell with the pure La9.5Ge5.5Nb0.5O26.5 as its electrolyte material superior to those of the SOFC cells with a YSZ electrolyte of comparable thickness shown in the literature.
Keywords Solid oxide fuel cell; Apatite; Impedance; Cell performance
Remark Link

Transformation from insulating p-type to semiconducting n-type conduction in CaCu3Ti4O12-related Na(Cu5/2Ti1/2)Ti4O12 ceramics

Authors Li, Ming, Sinclair, Derek C.
Source
Journal of Applied Physics
Volume: 114, Issue: 3, Pages: 034106 - 034106-8
Time of Publication: 2013-07
Abstract A double doping mechanism of Na+ + ½ Ti4+ → Ca2+ + ½ Cu2+ on the general formula Ca1-xNax(Cu3-x/2Tix/2)Ti4O12 has been used to prepare a series of isostructural CaCu3Ti4O12 (CCTO)-type perovskites. A complete solid solution exists for 0 ≤ x ≤ 1 and all compositions exhibit incipient ferroelectric behaviour with higher than expected intrinsic relative permittivity. Although CCTO ceramics typically exhibit n-type semiconductivity (room temperature, RT, resistivity of ∼10–100 Ω cm), Na(Cu5/2Ti1/2)Ti4O12 (NCTO) ceramics sintered at 950 C consist of two insulating bulk phases (RT resistivity > 1 GΩ cm), one p-type and the other n-type. With increasing sintering temperature/period, the p-type phase transforms into the n-type phase. During the transformation, the resistivity and activation energy for electrical conduction (Ea ∼ 1.0 eV) of the p-type phase remain unchanged, whereas the n-type phase becomes increasingly conductive with Ea decreasing from ∼ 0.71 to 0.11 eV with increasing sintering temperature. These changes are attributed to small variations in stoichiometry that occur during high temperature ceramic processing with oxygen-loss playing a crucial role.
Remark Link

New double molybdate Na9Fe(MoO4)6: Synthesis, structure, properties

Authors Aleksandra A. Savina, Sergey F. Solodovnikov, Olga M. Basovich, Zoya A. Solodovnikova, Dmitry A. Belov, Konstantin V. Pokholok, Irina A. Gudkova, Sergey Yu. Stefanovich, Bogdan I. Lazoryak, Elena G. Khaikina
Source
Journal of Solid State Chemistry
Volume: 205, Pages: 149–153
Time of Publication: 2013-09
Abstract A new double molybdate Na9Fe(MoO4)6 was synthesized using solid state reactions and studied with X-ray powder diffraction, second harmonic generation (SHG) technique, differential scanning calorimetry, X-ray fluorescence analysis, Mssbauer and dielectric impedance spectroscopy. Single crystals of Na9Fe(MoO4)6 were obtained and its structure was solved (the space group RView the MathML source3, a=14.8264(2), c=19.2402(3) , V=3662.79(9) 3, Z=6, R=0.0132). The structure is related to that of sodium ion conductor II-Na3Fe2(AsO4)3. The basic structure units are polyhedral clusters composed of central FeО6 octahedron sharing edges with three Na(1)О6 octahedra. The clusters share common vertices with bridging МоО4 tetrahedra to form an open 3D framework where the cavities are occupied by Na(2) and Na(3) atoms. The compound melts incongruently at 904.70.2 K. Arrhenius type temperature dependence of electric conductivity σ has been registered in solid state (σ=6.810−2 S сm−1 at 800 K), thus allowing considering Na9Fe(MoO4)6 as a new sodium ion conductor.
Keywords Sodium–iron molybdate; Crystal structure; Solid-state electrolyte
Remark Link

Study of bulk and grain-boundary conductivity of Ln2+xHf2−xO7−δ (Ln = Sm-Gd; x = 0, 0.096) pyrochlores

Authors A. V. Shlyakhtina, S. N. Savvin, A. V. Levchenko, A. V. Knotko, Petra Fedtke, Andreas Busch, Torsten Barfels, Marion Wienecke, L. G. Shcherbakova
Source
Journal of Electroceramics
Volume: 24, Issue: 4, Pages: 300-307
Time of Publication: 2010-06
Abstract The electrical conductivity of new solid electrolytes Eu2.096Hf1.904O6.952 and Gd2Hf2O7 have been compared with those for different pyrochlores including titanates and zirconates Ln2+xМ2−xO7−δ (Ln = Sm-Lu; M = Ti, Zr; x = 0−0.81). Impedance spectroscopy data demonstrate that Eu2.096Hf1.904O6.952 and Gd2Hf2O7 synthesized from mechanically activated oxides have high ionic conductivity, comparable to that of their zirconate analogues. The bulk and grain-boundary components of conductivity in Sm2.096Hf1.904O6.952 (Тsynth = 1600С), Eu2.096Hf1.904O6.952 and Gd2Hf2O7 (Тsynth = 1670С) have been determined. The highest bulk conductivity is offered by the disordered pyrochlores prepared at 1600C and 1670C: ~1.5  10−4 S/cm for Sm2.096Hf1.904O6.952, 5  10−3 S/cm for Eu2.096Hf1.904O6.952 and 3  10−3 S/cm for Gd2Hf2O7 at 780С, respectively. The conductivity of the fluorite-like phases at the phase boundaries of the Ln2+xМ2−xO7−δ (Ln = Eu, Gd; M = Zr, Hf; x ~ 0.286) solid solutions, as well as that of the high-temperature fluorite-like phases Ln2+xМ2−xO7−δ (Ln = Eu, Gd; M = Zr, Hf; x = 0−0.286), is lower than the conductivity of the disordered pyrochlores Ln2+xМ2−xO7−δ (Ln = Eu, Gd; M = Zr, Hf; x = 0−0.096).
Remark Link

Ionic conduction in glasses in the MnNbOF5-BaF2-BiF3 system

Authors S. A. Polyshchuk, L. N. Ignat’eva, S. L. Sinebryukhov, S. V. Gnedenkov, A. B. Podgorbunsky, N. N. Savchenko, A. B. Slobodyuk, V. M. Bouznik
Source
Russian Journal of Inorganic Chemistry
Volume: 58, Issue: 4, Pages: 387-391
Time of Publication: 2013-04
Abstract The electrical conductivity of oxyfluoride glasses in the MnNbOF5-BaF2-BiF3 system in the temperature range 299–550 K was studied by impedance spectroscopy. It was shown that the conductivity is mainly caused by fluoride ions forming fluorobismuth polyhedra in the glass structure, being as high as 7.46 10−3 S/cm (533 K) in the 20MnNbOF5-30BaF2-50BiF3 system reaches, which is at the level of the best values for fluoride glasses.
Remark Link

Solid-state photoelectrochemical H2 generation with gaseous reactants

Authors Kingsley O. Iwu, Augustinas Galeckas, Andrej Yu. Kuznetsov, Truls Norby
Source
Electrochimica Acta
Volume: 97, Pages: 320–325
Time of Publication: 2013-05
Abstract Photocurrent and H2 production were demonstrated in an all solid-state photoelectrochemical cell employing gaseous methanol and water vapour at the photoanode. Open circuit photovoltage of around -0.4 V and short circuit photocurrent of up to 250 μA/cm2 were obtained. At positive bias, photocurrent generation was limited by the irradiance, i.e., the amount of photogenerated charge carriers at the anode. Time constants and impedance spectra showed an electrochemical capacitance of the cell of about 15 μF/cm2 in the dark, which increased with increasing irradiance. With only water vapour at the anode, the short circuit photocurrent was about 6% of the value with gaseous methanol and water vapour. The photoanode and electrocatalyst on carbon paper support were affixed to the proton conducting membrane using Nafion as adhesive, an approach that yielded photocurrents up to 15 times better than that of a cell assembled by hot-pressing, in spite of the overall cell resistance of the latter being up to 5 times less than that of the former. This is attributed, at least partially, to reactants being more readily available at the photoanode of the better performing cell.
Keywords Photoelectrochemical; hydrogen; TiO2; solid-state; Nafion
Remark Link

Metallic Interconnects for Proton Ceramic Fuel Cells. Oxidation behavior and transport properties under simulated fuel cell conditions

Author Anders Werner Bredvei Skilbred
Source
Time of Publication: 2013-03
Remark Dissertation for the degree of Philosophiae Doctor
Link

Synthesis and characterization of perovskite-type SrxY1−xFeO3−δ (0.63≤x<1.0) and Sr0.75Y0.25Fe1−yMyO3−δ (M= Cr, Mn, Ni), (y=0.2, 0.33, 0.5)

Authors J.J. Biendicho, S. Shafeie, L. Frenck, D. Gavrilova, S. Bhme, A.M. Bettanini, P. Svedlindh, S. Hull, Z. Zhao, S.Ya. Istomin, J. Grins, G. Svensson
Source
Journal of Solid State Chemistry
Volume: 200, Pages: 30-38
Time of Publication: 2013-04
Abstract Abstract Oxygen-deficient ferrates with the cubic perovskite structure SrxY1−xFeO3−δ were prepared in air (0.71≤x≤0.91) as well as in N2 (x=0.75 and 0.79) at 1573 K. The oxygen content of the compounds prepared in air increases with increasing strontium content from 3-δ=2.79(2) for x=0.75 to 3-δ=2.83(2) for x=0.91. Refinement of the crystal structure of Sr0.75Y0.25FeO2.79 using TOF neutron powder diffraction (NPD) data shows high anisotropic atomic displacement parameter (ADP) for the oxygen atom resulting from a substantial cation and anion disorder. Electron diffraction (ED) and high-resolution electron microscopy (HREM) studies of Sr0.75Y0.25FeO2.79 reveal a modulation along <1 0 0>p with G ~0.4<1 0 0>p indicating a local ordering of oxygen vacancies. Magnetic susceptibility measurements at 5–390 K show spin-glass behaviour with dominating antiferromagnetic coupling between the magnetic moments of Fe cations. Among the studied compositions, Sr0.75Y0.25FeO2.79 shows the lowest thermal expansion coefficient (TEC) of 10.5 ppm K−1 in air at 298–673 K. At 773–1173 K TEC increases up to 17.2 ppm K−1 due to substantial reduction of oxygen content. The latter also results in a dramatic decrease of the electrical conductivity in air above 673 K. Partial substitution of Fe by Cr, Mn and Ni according to the formula Sr0.75Y0.25Fe1−yMyO3−δ (y=0.2, 0.33, 0.5) leads to cubic perovskites for all substituents with y=0.2. Their TECs are higher in comparison with un-doped Sr0.75Y0.25FeO2.79. Only M=Ni has increased electrical conductivity compared to un-doped Sr0.75Y0.25FeO2.79.
Keywords Perovskites; Neutron diffraction; Electron diffraction; High-temperature conductivity; Thermal expansion; Magnetic susceptibility
Remark Link

Optimization of synthesis conditions for rare-earth titanate based oxygen ion conductors

Authors A.V. Shlyakhtina, D.A. Belov, S.Yu. Steafanovich, E.A. Nesterova, O.K. Karyagina, L.G. Shcherbakova
Source
Solid State Ionics
Volume: 230, Pages: 52-58
Time of Publication: 2013-01
Abstract High-density (Yb0.9Ca0.1)2Ti2O6.9, (Yb0.8Ca0.1Tb0.1)2Ti2O7 − δ, and (Dy0.8Ca0.1Tb0.1)2Ti2O7 − δ solid solutions have been prepared through co-precipitation followed by firing for 4 h at 1500 and 1550 C, and their crystal structure (XRD), microstructure (SEM), and oxygen ion conductivity (impedance spectroscopy) have been studied in relation to the firing temperature and precipitant used. As in the case of (Yb0.9Ca0.1)2Ti2O6.9 and (Yb0.8Ca0.1Tb0.1)2Ti2O7 − δ, the optimal synthesis temperature for (Dy0.8Ca0.1Tb0.1)2Ti2O7 − δ is 1500 C. The bulk oxygen ion conductivity of the pyrochlore-like solid solutions (Yb0.9Ca0.1)2Ti2O6.9 is a stronger function of synthesis temperature than that of the (Dy0.8Ca0.1Tb0.1)2Ti2O7 − δ and (Yb0.8Ca0.1Tb0.1)2Ti2O7 − δ solid solutions with more complex A sublattice. The rise of the synthesis temperature from 1500 to 1550 C has detrimental effect on the grain boundary conductivity of the (Yb0.9Ca0.1)2Ti2O6.9 and (Dy0.8Ca0.1Tb0.1)2Ti2O7 − δ ceramics. That effect is connected with a considerable grain-boundary segregation of a calcium-containing phase in the (Yb0.9Ca0.1)2Ti2O6.9 and (Dy0.8Ca0.1Tb0.1)2Ti2O7 − δ. The bulk and grain boundary conductivity of (Dy0.8Ca0.1Tb0.1)2Ti2O7 − δ are independent of the precursor synthesis conditions (homogeneous and non-homogeneous co-precipitation).
Keywords Synthesis; Co-precipitation; Pyrochlore; Doping; Oxide ion conductivity; Impedance spectroscopy
Remark Link

Multilayered thin films for oxidation protection of Mg2Si thermoelectric material at middle–high temperatures

Authors S. Battiston, S. Boldrini, S. Fiameni, A. Famengo, M. Fabrizio, S. Barison
Source
Thin Solid Films
Volume: 526, Pages: 150–154
Time of Publication: 2012-12
Abstract Multilayered molybdenum silicide-based thin films were deposited via radio frequency magnetron sputtering in order to obtain efficient barrier against oxidation process which affected Mg2Si thermoelectric materials at middle–high temperatures. X ray diffraction, energy dispersive spectroscopy, secondary ion mass spectroscopy, field emission scanning electron microscopy (FE-SEM) and electrical measurements at high temperature were carried out in order to obtain, respectively, the structural, compositional, morphological and electrical characterization of coatings. Furthermore, the mechanical behavior of the thin film/Mg2Si-pellet system was observed in situ as a function of temperature by FE-SEM employing a heating module. Moreover, the barrier properties for oxygen protection after thermal treatment in air at high temperature were qualitatively evaluated.
Keywords Thin film; Thermoelectric material; Magnesium silicide; Molybdenum silicide; Middle–high temperature
Remark Link

Thin films of SnO2-CeO2 binary oxides obtained by pulsed laser deposition for sensing application

Authors Simona Somacescua, Rares Scurtu, George Epurescu, Rovena Pascu, Bogdana Mitu, Petre Osiceanu, Maria Dinescu
Source
Applied Surface Science
Time of Publication: 2012-11
Abstract Binary tin oxide – cerium oxide thin films with ceria concentrations in the range 10- 30% have been obtained by pulsed laser deposition technique, with or without additional oxygen RF plasma beam assistance. A good preservation of the Ce/Sn atomic concentration and Ce3+ content on the film surface of about 30% was obtained for almost all the investigated conditions of substrate temperature and RF powers. The sharp decrease of the electrical resistance in hydrogen environment at temperatures above 300 C indicates a direct interaction between hydrogen and metal oxides surfaces leading to OH groups formation, as evidenced by XPS measurements. The highest sensitivity (∼40) was attained for the sample with 10% ceria and RF assistance, while the lowest operating temperature (∼250-320 C) was encountered for that with 30% ceria deposited in the presence of RF discharge.
Keywords RF assisted pulsed laser deposition; SnO2-CeO2 binary oxides; Ce3+ and Ce4+ concentration; sensitivity in H2 atmosphere
Remark Available online
Link

Phase formation, electrical properties and morphotropic phase boundary of 0.95Pb(ZrxTi1−x)O3–0.05Pb(Mn1/3Nb2/3)O3 ceramics

Authors Anurak Prasatkhetragarna, Rattikorn Yimnirun
Source
Ceramics International
Volume: 39, Pages: S91–S95
Time of Publication: 2013-05
Abstract Ferroelectric ceramics in specific composition of 0.95Pb(ZrxTi1−x)O3–0.05Pb(Mn1/3Nb2/3)O3 or PZT–PMnN (with x=0.46, 0.48, 0.50, 0.52, and 0.54) have been investigated in order to identify the morphotropic phase boundary (MPB) composition. The effects of Zr/Ti ratio on phase formation, dielectric and ferroelectric properties of the specimens have also been investigated and discussed. X-ray diffraction patterns indicate that the MPB of the tetragonal and rhombohedral phase lies in x=0.52. The crystal structure of PZT–PMnN appeared to change gradually from tetragonal to rhombohedral phase with increasing Zr content. The dielectric and ferroelectric properties measurements also show a maximum value (εr, tan δ and Pr) at Zr/Ti=52/48, while the transition temperature decreases with increasing Zr content.
Keywords Dielectric properties; Ferroelectric properties; MPB
Remark Link

Oxygen ion conductivity of (Yb0.9 − xTbxCa0.1)2Ti2O7 − δ solid solutions

Authors A. V. Shlyakhtina, D. A. Belov, S. Yu. Stefanovich, O. K. Karyagina and L. G. Shcherbakova
Source
Inorganic Materials
Volume: 48, Issue: 11, Pages: 1126-1130
Time of Publication: 2012-11
Abstract We have studied terbium substitution for ytterbium in (Yb0.9 − x Tb x Ca0.1)2Ti2O7 − δ (x = 0.1, 0.2, 0.3, 0.4) pyrochlore solid solutions synthesized through coprecipitation followed by firing at 1550C. The results indicate that only a small amount of terbium (less than 10%) can be incorporated into the pyrochlore structure of (Yb0.9Ca0.1)2Ti2O6.9 because of the large difference in ionic radius between the terbium and ytterbium cations: Δr = r(TbCN 83+) − r(YbCN 83+) = 0.055 . The oxygen ion conductivity of the (Yb0.9 − x Tb x Ca0.1)2Ti2O7 − δ solid solutions has been determined by impedance spectroscopy in air in the temperature range 300 to 900C. At high temperatures (t > 640C), their bulk conductivity was essentially independent of the Yb/Tb ratio. The observed decrease in density and microstructural changes were insignificant. At relatively low temperatures (t < 640C), the bulk conductivity decreased slightly, and the decrease depended little on terbium concentration.
Remark Link

H and Li Related Defects in ZnO and their Effect on Electrical Properties

Authors Tor Svendsen Bjrheim , Skjalg Erdal , Klaus Magnus Johansen , Knut Erik Knutsen , and Truls Norby
Source
J. Phys. Chem. C
Volume: 166, Issue: 44, Pages: 23764–23772
Time of Publication: 2012-10
Abstract Li and H are important electrically active impurities in ZnO and this work presents a detailed experimental and computational study of the behavior of H and Li in ZnO, and their effect on its defect structure. We employ AC conductivity measurements as a function of temperature and partial pressure of O2, H2O and D2O, which is combined with first principles density functional theory (DFT) calculations and thermodynamic modeling (TDM) of finite temperature defect structures in undoped and Li doped ZnO. Undoped ZnO is dominated by protons as hydroxide defects (OH_O^•), oxygen vacancies (v_O^(••)) and electrons under a large variety of atmospheric conditions, and we also predict from DFT and TDM the substitutional hydride ion (H_O^•) to dominate concentration-wise under the most reducing conditions at temperatures above 500 C. The equilibrium concentrations of defects in ZnO are small, and dopants such as Li strongly affect the electrical properties. Experimentally, Li doped ZnO is found to be n-type under all available atmospheric conditions and temperatures, with a n-type conductivity significantly lower than that of as-grown ZnO. The n-type conductivity also increases with decreasing p_(O_2 ) and with increasing p_(H_2 O). The observed electrical properties of Li doped ZnO are attributed to dominance of the ionic defects Li_Zn^/, OH_O^•, Li_i^•, v_O^(••), and the neutral complexes (Li_Zn OH_O)^ and (Li_Zn Li_i)^. Although Li doping lowers the Fermi level of as-grown ZnO significantly, low formation energy of the ionic donors, and passivation of Li_Zn^/ in the form of (Li_Zn OH_O)^ and (Li_Zn Li_i)^, prevents realization of significant/stable p-type activity in Li doped ZnO under equilibrium conditions.
Remark Link

Crystal structure, hydration and ionic conductivity of the inherently oxygen-deficient La2Ce2O7

Authors Vasileios Besikiotis, Christopher S. Knee, Istaq Ahmed, Reidar Haugsrud, Truls Norby
Source
Solid State Ionics
Volume: 228, Pages: 1–7
Time of Publication: 2012-11
Abstract The crystal structure, hydration and ionic conductivity of the inherently oxygen deficient La2Ce2O7 system have been investigated. On the basis of Rietveld analysis of neutron diffraction data, the material is found to adopt a cation disordered oxygen-deficient fluorite structure. Impedance spectroscopy, performed in the temperature range 1000–200 C and as a function of water vapor and oxygen partial pressure, suggests that oxide ion conductivity dominates at high temperatures, while protons are the main charge carrier at temperatures below approximately 450 C. Proton conductivity was confirmed by isotope shifts under H2O and D2O. The dissolution of water was measured by means of thermogravimetry (TG). A defect chemical model is developed to derive hydration thermodynamic parameters based on TG and conductivity data. The hydration enthalpy was, moreover, determined directly by simultaneous TG and differential scanning calorimetry (TG–DSC). The TG–DSC values were in good agreement with those modeled from conductivity and TG data.
Keywords La2Ce2O7; Proton conductivity; Pyrochlore structure; Fluorite structure; Nonstoichiometric oxides
Remark Link

Microstructure and electrical properties of zirconia and composite nanostructured ceramics sintered by different methods

Authors Bogdan Stefan Vasile, Ecaterina Andronescu, Cristina Ghitulica, Otilia Ruxandra Vasile, Lavinia Curechiu, Rares Scurtu, Eugeniu Vasile, Roxana Trusca, Livia Pall, Virgil Aldica
Source
Ceramics International
Volume: 39, Issue: 3, Pages: 2535–2543
Time of Publication: 2013-04
Abstract The aim of this study is the preparation and characterization of dense cubic zirconia ceramics and zirconia nanocomposites (reinforced with 5 wt% alumina). The powders were obtained through sol–gel methods and densified using classical sintering and spark plasma sintering (SPS) methods. The obtained ceramics were characterized through X-ray diffraction, scanning electron microscopy and impedance spectroscopy at room and high temperature. The average grain size of cubic zirconia particles was found to be approximately 8 and 2.5 μm for the classical sintering and 99 nm for SPS. The alumina particles in composites have an average grain size of 0.7 μm for classical sintering and 53 nm for SPS ones. The total conductivity for nanocomposites sintered through both methods was also determined.
Remark Link

Characteristics of SrCo1 − xSnxO3 − δ cathode materials for use in solid oxide fuel cells

Authors Sea-Fue Wang, Yung-Fu Hsu, Chun-Ting Yeh, Chien-Chung Huang, Hsi-Chuan Lu
Source
Solid State Ionics
Volume: 227, Pages: 10–16
Time of Publication: 2012-10
Abstract In this study, introduction of tin ions in the SrCoO3 − δ oxide is attempted to modify its electrochemical behavior for serving as a cathode of intermediate-temperature solid oxide fuel cells (IT-SOFCs). Doping of tin ions appears to stabilize the cubic Pm-3m phase of the SrCo1 − ySnyO3 − δ ceramics but generates SrSnO3 precipitates and inhibits the grain growth as y value rises to a level greater than 10%. Obtained at 550 C, the maximum electrical conductivity of SrCo0.95Sn0.05O3 − δ reads 545 S cm− 1. Single cells with a structure of NiO–Sm0.2Ce0.8O2 − δ (SDC)/SDC/SrCo0.95Sn0.05O3 − δ–SDC are built and characterized. Though SrCo0.95Sn0.05O3 − δ is regarded as an MIEC (mixed ionic/electronic conductivity material), adding SDC to SrCo0.95Sn0.05O3 − δ guarantees good adhesion to and fine electrical contact with the electrolyte layer, thereby contributing to the reduction in R0 and RP values. The single cell with the SrCo0.95Sn0.05O3 − δ–SDC composite cathode at 700 C registers respectively an R0 value of 0.044 Ω cm2 and an RP value of 0.109 Ω cm2. In the absence of microstructure optimization and hermetic sealing of cells, a high power density of 0.847 W cm− 2 is reached. SrCo1 − ySnyO3 − δ thus emerges to be a promising cathode material for IT-SOFCs applications.
Keywords Solid oxide fuel cell; Cathode; Impedance; Cell performance
Remark Link

Investigation of La1−xSrxCrO3−∂ (x ~ 0.1) as Membrane for Hydrogen Production

Authors Yngve Larring, Camilla Vigen, Florian Ahouanto, Marie-Laure Fontaine, Thijs Peters, Jens B. Smith, Truls Norby and Rune Bredesen
Source
Membranes
Volume: 2, Issue: 3, Pages: 665-686
Time of Publication: 2012-09
Abstract Various inorganic membranes have demonstrated good capability to separate hydrogen from other gases at elevated temperatures. Hydrogen-permeable, dense, mixed proton-electron conducting ceramic oxides offer superior selectivity and thermal stability, but chemically robust candidates with higher ambipolar protonic and electronic conductivity are needed. In this work, we present for the first time the results of various investigations of La1−xSrxCrO3−∂ membranes for hydrogen production. We aim in particular to elucidate the material’s complex transport properties, involving co-ionic transport of oxide ions and protons, in addition to electron holes. This opens some new possibilities for efficient heat and mass transfer management in the production of hydrogen. Conductivity measurements as a function of pH2 at constant pO2 exhibit changes that reveal a significant hydration and presence of protons. The flux and production of hydrogen have been measured under different chemical gradients. In particular, the effect of water vapor in the feed and permeate gas stream sides was investigated with the aim of quantifying the ratio of hydrogen production by hydrogen flux from feed to permeate and oxygen flux the opposite way (“water splitting”). Deuterium labeling was used to unambiguously prove flux of hydrogen species.
Keywords hydrogen transport membrane; proton permeation; oxygen permeation; water splitting
Remark Link

CO2 decomposition via oxygen deficient ferrite electrodes using solid oxide electrolyser cell

Source
Time of Publication: 2012-09
Abstract Oxygen Deficient Ferrites (ODF) electrodes integrated with Yttria Stabilized Zirconia (YSZ) electrolyte, electrochemically decompose carbon dioxide (CO2) into carbon (C)/carbon monoxide (CO) and oxygen (O2) in a continuous process. The ODF electrodes can be kept active by applying a small potential bias across the electrodes. CO2 and water (H2O) can also be electrolyzed simultaneously to produce syngas (H2+CO) and O2 continuously that can be fed back to the oxy-fuel combustion. With this approach, CO2 can be transformed into a valuable fuel source allowing CO2 neutral use of the hydrocarbon fuels.
Remark United States Patent Application 20120228150
Link

Transient Oxygen Permeation and Surface Catalytic Properties of Lanthanum Cobaltite Membrane under Oxygen–Methane Gradient

Author Tyler T. Norton and Y. S. Lin
Source
Ind. Eng. Chem. Res.
Volume: 51, Issue: 39, Pages: 12917–12925
Time of Publication: 2012-09
Abstract Oxygen permeation through mixed-conducting ceramic membranes in an air/methane gradient is important for their applications in membrane reactors for air separation and partial oxidation of hydrocarbons. This study examines transient characteristics of oxygen permeation and surface catalytic properties of La0.6Sr0.4Co0.8Fe0.2O3-δ (LSCF) membranes in an oxygen/methane gradient for an extended period of time. Upon exposure to an oxygen/methane gradient, the oxygen permeation flux of the membrane increases to a maximum at around 55 h, then decreases and reaches a steady-state value at around 200 h. The maximum and steady-state flux is approximately 60% and 30% higher than the initial flux of the fresh membrane, respectively. The surface catalytic properties of the membrane exposed to methane also change with the exposure time in a similar fashion. However, the apparent activation energy for oxygen permeation for the membranes at various stages of the transient study is nearly constant while the effects of temperature, feed pressure, and sweep flow rate on catalytic properties are also similar for the fresh and aged membranes. The surface of a LSCF membrane reacts with methane resulting in a formation of a thin porous layer which changes the surface catalytic properties. The membrane surface becomes more active for reaction with increased selectivity for carbon monoxide formation upon exposure to methane. This lowers oxygen partial pressure in the permeate side and increases the driving force for oxygen permeation and, therefore, increases oxygen permeation flux. Under the studied experimental conditions the membrane can reach steady-state for continuous operation.
Remark Link

Fabrication, sealing and high pressure testing of tubular La2NiO4+δ membranes for air separation

Authors Paul Inge Dahl, Marie-Laure Fontaine, Florian Ahouanto, Christelle Denonville, Ove Paulsen, Yngve Larring, Thijs Peters, Partow Pakdel Henriksen, Rune Bredesen
Source
Energy Procedia
Volume: 23, Pages: 187–196
Time of Publication: 2012-09
Abstract Recent results achieved on fabrication of La2NiO4+δ membranes, sealing technology and performance in pressurized conditions are presented. Porous tubular membrane supports of up to 1 m length are prepared by ceramic extrusion. Asymmetric La2NiO4+δ membranes are prepared by coating dense selective layers of 10-15 μm thickness onto the porous supports. Glass ceramic seals in the system Na2O-CaO-Al2O3-SiO2 are currently being evaluated for joining the membranes with high temperature steel alloys coated with a corrosion resistance protective layer. By adjusting the composition of the glass system the thermal expansion coefficient is tailored to match that of the membrane and steel material. Good seal adherences towards these materials are obtained. Long term oxygen flux measurements (>4000 hours continuous operation) performed on symmetric (dense) La2NiO4+δ membranes are conducted under various conditions (atmosphere, temperature, pressure). The oxygen flux dependency on the oxygen partial pressure (pO2) is investigated by increasing the feed pressure and oxygen content. An asymptotic flux behavior is observed with increasing pO2. It is seen a significant increase in the flux (by a factor of 6) when increasing the feed pO2 from 0.8 to 2.4 bars while a less significant pO2 dependency is observed with further increase.
Keywords Oxygen transport membranes; fabrication; sealing; pressurized testing
Remark Link

Effects of the microwave heating on the properties of gadolinium-doped cerium oxide prepared by polyol method

Authors A. Gondolini, E. Mercadelli, A. Sanson, S. Albonetti, L. Doubova, S. Boldrini
Source
Journal of the European Ceramic Society
Volume: 33, Issue: 1, Pages: 67–77
Time of Publication: 2013
Abstract Gadolinium doped ceria (GDC) has received a lot of attention as possible electrolyte material for Intermediate-Temperature (500–800 C) Solid Oxide Fuel Cells (IT-SOFC). Microwave heating has been recently considered in combination with precipitation for the production of oxide or non-oxide nano-powders. In this study, crystalline CeO2 powders doped with different amount of gadolinium were successfully prepared by microwave-assisted polyol method under mild conditions and in one single step. The microwave heating was found to strongly influence the morphological properties of the powder especially for low gadolinium content. IR and thermal analyses helped to identify the major reaction path for the formation of the as-observed complex morphologies. Regardless to the morphology, the powders showed good densification behavior and expected electrochemical properties; Ce0.9Gd0.1O1.95 exhibited the highest conductivity.
Keywords Doped ceria; Microwave processing; Ionic conductivity; Fuel cells; Polyol method
Remark Link

Investigating Reliability on Fuel Cell Model Identification. Part II: An Estimation Method for Stochastic Parameters

Authors L. Tsikonis, S. Diethelm, H. Seiler, A. Nakajo, J. Van herle, D. Favrat
Source
Fuel Cells
Time of Publication: 2012-08
Abstract An alternative way to process data from polarization measurements for fuel cell model validation is proposed. The method is based on re- and subsampling of I–V data, with which repetitive estimations are obtained for the model parameters. This way statistics such as standard deviations and correlations between the parameters may be experimentally derived. Histograms may also be produced, approximating the probability distributions that they follow. Two experimental case studies are discussed. In the first case, observations are made on the behavior of the parameter values for two mathematical models. As the number of data points (measurement points) employed in the estimation of the parameters increases, parameters with high variances converge to specific values. On the contrary, parameters with small variances diverge linearly. The parameters' histograms do not usually follow normal distributions rather they show a connection between the number of peaks in the graphs and correlations of the parameters. The second case study is an application on a fast degraded SOFC button cell, where the values and the histograms of the parameters are compared before and after degradation.
Keywords Data Fitting; Design of Experiments; Diagnostics; Fast Degradation; Identification; Parameter Estimation; Polarization Curves; Robust Regression; Solid Oxide Fuel cells; Stein's Paradox
Remark DOI: 10.1002/fuce.201200031
Link

Extending the family of oxygen ion conductors isostructural with La2Mo2O9

Authors V.I. Voronkova, E.P. Kharitonova, E.I. Orlova, D.A. Belov
Source
Journal of Solid State Chemistry
Volume: 196, Pages: 45–51
Time of Publication: 2012-12
Abstract X-ray diffraction characterization of materials prepared by solid-state reactions in the ternary systems La2Mo2O9–Nd2W2O9–“Nd2Mo2O9” and La2Mo2O9–Pr2W2O9–Pr2Mo2O9 has shown that, in these systems, compounds isostructural with the oxygen ion conductor La2Mo2O9 exist in wide single-phase regions. Partial tungsten substitution for molybdenum may yield stable Ln2Mo2−2xW2xO9 compounds with the La2Mo2O9 structure, where Ln is a rare-earth element different from lanthanum and praseodymium, e.g., neodymium. Tungsten also stabilizes Pr2Mo2O9, which otherwise decomposes above 700 C. A series of continuous solid solution was found in the La2Mo2O9–Pr2Mo2O9 system. Polymorphism of compounds existing in the above ternary systems was studied by differential scanning calorimetry. The conductivity of most of the compounds studied approaches that of lanthanum molybdate.
Remark Link

BaTiO3–Bi(Zn1/2Ti1/2)O3–BiScO3 Ceramics for High-Temperature Capacitor Applications

Authors Natthaphon Raengthon, Tutu Sebastian, Denis Cumming, Ian M. Reaney, David P. Cann
Source
Journal of the American Ceramic Society
Volume: 95, Issue: 11, Pages: 3554–3561
Time of Publication: 2012-09
Abstract Ceramics based on solid solutions of xBaTiO3–(100−x)(0.5Bi(Zn1/2Ti1/2)O3–0.5BiScO3), where x = 50, 55, and 60 were prepared by solid-state reaction which resulted in a single perovskite phase with pseudocubic symmetry. Dielectric property measurements revealed a high relative permittivity (>1000), which could be modified with the addition of Bi(Zn1/2Ti1/2)O3 (BZT) and BiScO3 (BS) to engineer a temperature-stable dielectric response with a temperature coefficient of permittivity (TCε) as low as −182 ppm/C. By incorporating 2 mol% Ba vacancies into the stoichiometry, the resistivity increased significantly, especially at high temperatures (>200C). Vogel–Fulcher analysis of the permittivity data showed that the materials exhibited freezing of polar nanoregions over the range of 100–150 K. An analysis of optical absorption near the band edge for the Ba-deficient compositions suggested that the enhanced resistivity values were linked to a decrease in the concentration of defect states. An activation energy of ~1.4 eV was obtained from DC resistivity measurements suggesting that an intrinsic conduction mechanism played a major role in the high temperature conductivity. Finally, multilayer capacitors based on these compositions were fabricated, which exhibited dielectric properties comparable to the bulk material. Based on these results, this family of materials has great promise for high-temperature capacitor applications.
Remark Link

Sr1−xPrxCo0.95Sn0.05O3−δ ceramic as a cathode material for intermediate-temperature solid oxide fuel cells

Authors Sea-Fue Wang, Yung-Fu Hsu, Hsi-Chuan Lu, Chien-Chung Huang, Chun-Ting Yeh
Source
International Journal of Hydrogen Energy
Volume: 37, Issue: 17, Pages: 12548–12556
Time of Publication: 2012-10
Abstract In this study, the physical properties of the Sr1−xPrxCo0.95Sn0.05O3−δ ceramics were measured and their potential for use as a cathode material of intermediate-temperature solid oxide fuel cells (IT-SOFCs) was evaluated. A cubic phase was retained in all of the Sr1−xPrxCo0.95Sn0.05O3−δ ceramics. Analysis of the temperature-dependent conductivity found the SrCo0.95Sn0.05O3−δ and Sr0.9Pr0.1Co0.95Sn0.05O3−δ ceramics exhibiting semiconductor-like behavior below 550 C and metal-like behavior above the same temperature. The Sr0.8Pr0.2Co0.95Sn0.05O3−δ and Sr0.7Pr0.3Co0.95Sn0.05O3−δ ceramics, however, reported a metal-like conductivity in the whole temperature range. The electrical conductivities of the Sr0.8Pr0.2Co0.95Sn0.05O3−δ ceramic at 500 C and 700 C read respectively 1250 S/cm and 680 S/cm, both of which were superior than those in most of the common perovskites. Single cells with a structure of NiO–Sm0.2Ce0.8O2−δ (SDC)/SDC/Sr0.8Pr0.2Co0.95Sn0.05O3−δ-SDC were built and characterized. Addition of SDC in Sr0.8Pr0.2Co0.95Sn0.05O3−δ emerged to be a crucial factor reducing the ohmic resistance (R0) and polarization resistance (RP) of the cell by facilitating a better adhesion to and electrical contact with the electrolyte layer. The R0 and RP of the cell read respectively 0.068 Ω cm2 and 0.0571 Ω cm2 at 700 C and 0.298 Ω cm2 and 1.310 Ω cm2 at 550 C. With no microstructure optimization and hermetic sealing of the cells, maximum power density (MPD) and open circuit voltage (OCV) reached respectively 0.872 W/cm2 and 0.77 V at 700 C and 0.482 W/cm2 and 0.86 V at 550 C. It is evident that Sr1−xPrxCo0.95Sn0.05O3−δ is a promising cathode material for IT-SOFCs.
Keywords Solid oxide fuel cell; Cathode; Impedance; Cell performance
Remark Link

Nitrogen and hydrogen defect equilibria in Ca12Al14O33: a combined experimental and computational study

Authors Jonathan M. Polfus , Kazuaki Toyoura , Charles H. Hervoches , Martin F. Sunding , Isao Tanaka and Reidar Haugsrud
Source
Journal of Materials Chemistry
Volume: 22, Pages: 15828-15835
Time of Publication: 2012-07
Abstract The defect structure of mayenite is investigated by Density Functional Theory (DFT) defect calculations; in situ electrical conductivity measurements in NH3 atmosphere at high temperature; and X-ray photoelectron spectroscopy (XPS) and gas phase mass spectrometry (GP-MS) of NH3 treated specimens. The computational results suggest that nitrogen is primarily incorporated substitutionally on oxygen sites as NH−2 and N3−. The concentration of nitrogen was estimated to be within the same order of magnitude by XPS, GP-MS and DFT, yielding a stoichiometry close to Ca12Al14O31.5N0.5:(NH2)0.5O0.5 which corresponds well with that obtained by Boysen et al. from similarly treated samples. Out diffusion of nitrogen was found to occur around 700 C in Ar by XPS, GP-MS and conductivity measurements, also in accordance with Boysen et al. The conductivity measurements showed that NH3 treatment had a significant effect on the defect structure of the material which became evident only after replacing the NH3 atmosphere with Ar: the conductivity increased abruptly due to a temporary non-equilibrium reduction of the material as nitrogen diffuses out while the lack of a sufficiently large source of oxygen in the surrounding atmosphere prevents the specimen from re-oxidizing. Further, based on the computational results and the pH2 dependency on conductivity after NH3 treatment, we propose dissolution of hydride ions from H2 in the reduced and highly conductive post-NH3 state.
Remark Link

Relaxor to Ferroelectric Transitions in (Bi1/2Na1/2)TiO3–Bi(Zn1/2Ti1/2)O3Solid Solutions

Authors Eric A. Patterson, David P. Cann
Source
Journal of the American Ceramic Society
Volume: 95, Issue: 11, Pages: 3509–3513
Time of Publication: 2012-11
Abstract Recently, (Bi1/2Na1/2)TiO3 solid solutions have been found to exhibit excellent dielectric and piezoelectric properties. In this study, the dielectric and ferroelectric properties of (1–x)(Bi1/2Na1/2)TiO3–xBi(Zn1/2Ti1/2)O3 (BNT–BZT) solid solutions were investigated. Up to a solubility limit of 8% BZT, distortions to the parent cubic perovskite phase were observed in the diffraction data through splitting of the (001), (011), and (111) reflections. At low concentrations of BZT, the material behaved very much like a conventional ferroelectric, with well-saturated loops with high remanent polarization (Pr ~ 35 μC/cm2). As the BZT content increased, the dielectric behavior displayed characteristics of relaxor behavior. Polarization hysteresis data at elevated temperatures and a thermal hysteresis in the dielectric maximum were evidence for a relaxor to ferroelectric transition.
Remark Link

Fabrication, structural and electrical characterization of Lanthanum Tungstate films by Pulsed Laser Deposition

Authors Einar Vollestad, Agnieszka Gorzkowska-Sobas, Reidar Haugsrud
Source
Thin Solid Films
Volume: 520, Issue: 21, Pages: 6531–6534
Time of Publication: 2012-08
Abstract Films of lanthanum tungstate, 3 μm in thickness, were fabricated by means of Pulsed Laser Deposition on a Pd foil. The films were characterized by X-ray diffraction, scanning electron microscopy, X-ray Photoelectron Spectroscopy and their electrical conductivity was measured at temperatures between 400 and 800 C in different gas atmospheres. The films’ structure and electrical characteristics are close to what is reported in the literature for corresponding polycrystalline material. The films exhibit fairly high proton conductivity at elevated temperatures, which make them interesting for components in hydrogen-related technologies. Changes in microstructure and the crystallographic orientation observed at higher temperatures were accompanied by changes in the conductivity characteristics.
Keywords Proton conducting oxide; ceramics; Hydrogen transport membrane; Films by Pulsed Laser Deposition; ionic conductor; lanthanum tungstate; La6WO12
Remark Link

Nd-doped Ba(Ce,Zr)O3 − δ proton conductors for application in conversion of CO2 into liquid fuels

Authors Wojciech Zając , Emil Hanc, Agnieszka Gorzkowska-Sobas, Konrad Świerczek, Janina Molenda
Source
Solid State Ionics
Volume: 225, Pages: 297–303
Time of Publication: 2012-10
Abstract The paper presents crystal structure, transport properties, chemical stability in CO2 atmosphere and thin film membrane preparation for materials from the Ba(Ce1 − xZrx)0.9Nd0.1O2.95 (x = 0, 0.25, 0.5, 0.75, 1) group of perovskite-type structure oxides. Transformation of crystal structure from orthorhombic Pnma to orthorhombic Imma and cubic with increasing xZr was observed along with linear decrease of pseudo-cubic unit cell volume and free lattice volume. Electrical conductivity of bulk and grain boundary was determined in dry air, as well as in air humidified with H2O or D2O. The highest proton conductivity was observed for material with xZr = 0.25. Further increase of Zr content led to decrease of conductivity as high as 2 orders of magnitude. This effect was coupled with bell-shape dependence of activation energy and pre-exponential term. Such behavior was explained as superimposed effects of high proton mobility for zirconium-rich materials due to cubic symmetry and cerium-rich materials due to softness of oxygen–oxygen separation distance, along with high proton concentration for cerium-rich perovskites. The deteriorating effect of grain boundaries on total electrical conductivity was far more pronounced for Zr-rich materials than in the case of Ce-rich ones. Declining grain boundary conductivity was attributed to both increase of number of grain boundaries and decrease of inherent grain boundary conductivity for Zr-rich samples. The highest chemical stability in CO2 atmosphere was achieved for high-Zr content materials, on the contrary, for BaCe0.9Nd0.1O2.95 in CO2 atmosphere, the decomposition onset temperature was below 500 C. 2 μm thin film membrane of Ba(Ce0.75Zr0.25)0.9Nd0.1O2.95 was successfully prepared on c-plane sapphire and fused silica substrates. Film's crystal structure matched that of the bulk material. The electrical conductivity of thermally treated film obtained on c-plane sapphire in wet air was 3.7 10− 4 S cm− 1 at 600 C.
Keywords Proton conductors; BaCeO3–BaZrO3 solid solutions; Isotope effect; Grain boundary effect; Thin films
Remark Link

High Curie temperature ternary piezoelectric ceramics

Authors Tan, Xiaoli (Ames, IA, US) Hu, Wei (Ames, IA, US)
Source
Time of Publication: 2012-06
Abstract A preferred piezoelectric ceramic material is a BiFeO3—PbZrO3—PbTiO3 ternary solid solution wherein proportions of the constituent perovskite metal oxides are selected so that the material exhibits relatively high Curie temperatures above 380 C. and useful piezoelectric properties.
Remark United States Patent Application 20120145943
Link

Hydrogen permeation, transport properties and microstructure of Ca-doped LaNbO4 and LaNb3O9 composites

Authors Wen Xing, Guttorm E. Syvertsen, Tor Grande, Zuoan Li, Reidar Haugsrud
Source
Journal of Membrane Science
Volume: 415-416, Pages: 878–885
Time of Publication: 2012-10
Abstract Two composites consisting of the proton conducting Ca-doped LaNbO4 and electron conducting LaNb3O9 with respectively 90 and 70 vol% LaNbO4 were prepared by spark plasma sintering. The amount of hydrogen produced at the sweep side was measured as a function of temperature and pH2 gradient under wet and dry sweep gas conditions. The hydrogen flux increases with increasing temperature and feed-sidepH2. The flux is significantly higher for the 70 vol% LaNbO4 composite than the 90 vol% LaNbO4 composite. Ambipolar conductivities calculated from the flux data showed the same pH2 dependence for both composites. The electrical conductivity of the 70 vol% LaNbO4 composite was characterized as a function of temperature under wet hydrogen. The microstructure and phase distribution of the two composites are analyzed and their transport properties with different flux limiting processes are discussed. An increased hydrogen production with wet compared to dry sweep gas is concluded to reflect water splitting due to transport of oxygen from the permeate to the feed side.
Keywords Hydrogen flux; Proton conductivity; Ceramic-ceramic composite; LaNbO4; LaNb3O9; Ambipolar conductivity; Water splitting
Remark Link

A novel coulometric titration setup—Principals, design and leakage minimization

Authors Mehdi Pishahang, Egil Bakken, Svein Stlen
Source
Thermochimica Acta
Time of Publication: 2012-05
Abstract This article presents a new coulometric titration setup and describes the principles of operation, the main precautions to be taken into account to reduce the systematic errors, and evaluates the working range and the accuracy of the measurements. The major source of error, the oxygen leakage, is studied in detail and modeled based on leakage of oxygen through the YSZ solid electrolyte. Decreasing the difference in chemical potential of oxygen between inside and outside of the cell is studied as an applied measure to decrease the oxygen leakage. Flushing the pumping solid electrolyte by N2 shows a reasonable improvement. Eventually, oxygen non-stoichiometry of SrFeO3−δ is measured at 1273 K in the oxygen partial pressure range of 0.6 < −log(pO2/atm) < 12. The resulting values are in good agreement with the literature.
Keywords Coulometric titration; Oxygen non-stoichiometry; Oxygen leakage

High Power Plasma Sprayed Intermediate Temperature Solid Oxide Fuel Cells with Sm0.5Sr0.5CoO3-δ Cathode

Authors Chang-sing Hwang , Chun-Huang Tsai, Chun-Liang Chang, Jen-Feng Yu, Sheng-Hui Nien
Source
Procedia Engineering
Volume: 36, Pages: 81–87
Time of Publication: 2012-05
Abstract The cells with porous Ni/Fe(∼10 wt%) metal plate as a supporting substrate, double layers of La0.75Sr0.25Cr0.5Mn0.5 O3-δ (LSCM) and nanostructured Ce0.55La0.45O2-δ/Ni (LDC/Ni) as an anode, LDC as an anode interlayer, La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) as an electrolyte, LSGM/Sm0.5Sr0.5CoO3-δ (SSC) as a cathode interlayer and SSC as a cathode current collector, were prepared by atmospheric plasma spraying (APS) coating processes followed by a heating treatment. The current-voltage-power and AC impedance measurement results show that the prepared cell heat-treated at 850 C for 3 hours in air with a dead load of 1000 g cm-2 has an attracting performance. The measured maximum output power densities of this cell have reached 0.777, 0.742, 0.659, 0.542, 0.393, and 0.250 W cm-2 at 800, 750, 700, 650, 600, and 550 C respectively. The measured ohmic and polarization resistances are 0.241, 0.254, 0.282, 0.328, 0.42, 0.62 and 0.055, 0.064, 0.083, 0.128, 0.23, 0.471 Ω cm2 at 800, 750, 700, 650, 600, and 550 C respectively. After correction of the resistance inside the ProboStat system, the predicted actual maximum power densities that a cell can deliver are 1.95, 1.613, 1.186, 0.823, 0.512, and 0.293 W cm-2 at 800, 750, 700, 650, 600, and 550 C respectively.
Keywords Atmospheric plasma spray; solid oxide fuel cells; metal-supported; nanostructured; Sm0.5Sr0.5CoO3-δ
Remark Link

Electromechanical strain in Bi(Zn1/2Ti1/2)O3–(Bi1/2Na1/2)TiO3–(Bi1/2K1/2)TiO3 solid solutions

Authors Eric A. Patterson, David P. Cann, Jan Pokorny, and Ian M. Reaney
Source
Journal of Applied Physics
Volume: 111, Issue: 9 Time of Publication: 2012-05
Abstract Solid solutions ceramics of the Bi(Zn0.5Ti0.5)O3–(Bi0.5K0.5)TiO3–(Bi0.5Na0.5)TiO3 ternary system for <20 mol. % BZT were created and confirmed to be single phase using x-ray diffraction. The dielectric dispersion showed decreasing Tmax of the dielectric spectrum with a broadening of the transition with increasing BZT content. At 2.5BZT–40BKT–57.5BNT, a secondary transition commonly observed for morphotropic phase boundary (MPB) BNT–BKT was observed. The ferroelectric behavior of the system was characterized by a transition where the polarization hysteresis showed a severe pinching effect on remanent polarization (20.8 μC/cm2 at 2.5% BZT) as BZT contents was increased (Pr = 2.3 μC/cm2 at 20% BZT). Similarly, as the temperature increased to 175 C, the remanent polarization of the 2.5% BZT composition significantly reduced to 2.1 μC/cm2. The onset of this transition corresponds to the lower temperature frequency dispersion observed in the dielectric spectrum. The strain hysteresis experienced analogous transition to the polarization, with a change in shape from typical ferroelectric butterfly to a complete loss of negative strain as BZT concentration increased. Maximum strain values of 0.33% were observed at 5-40-55 accompanied by a large d33* = 547pm/V.
Remark Published online 10 May 2012
Link

Process and Apparatus of CO2 Energy Source Adopted in Solid Oxide Fuel Cell - CO2 Energy Conversion Cycle

Authors M. Lee, C. Wang, Y. Chang, W. Kao, T. Lin, J. Chang, R. Yang, L. Lee
Source
Time of Publication: 2012-05
Abstract A process and apparatus of “Solid Oxide Fuel Cell (SOFC)-CO2 Energy Conversion Cycle (referred to as SOFC-CO2-ECC)” are invented to adopt CO2 as energy sources from waste/stock gas or convert and fix it in the useful compounds. CO2 is converted into CO and O2 via simultaneously catalytic and electrochemical reactions in SOFC for power generation and CO2 cracking. Furthermore, CO is used either as the fuel in SOFC for power generation or starting materials in the chemical reactors to produce CO-derivatives of energy source materials and useful chemical compounds. Hence, SOFC-CO2-ECC is an active or scientific carbon cycle with zero emission of CO2. Thus, the efficacy of environmental protection via solving the problem of CO2 greenhouse effect is achieved, so as to grasp of the “Right of Carbon Emission Trading” issues.
Remark United States Patent Application 20120115067
Link

Effect of doped ceria interlayer on cathode performance of the electrochemical cell using proton conducting oxide

Authors T. Sakai , S. Matsushita, J. Hyodo, Y. Okuyama, M. Matsuka, T. Ishihara, H. Matsumoto
Source
Electrochimica Acta
Volume: 75, Pages: 179–184
Time of Publication: 2012-07
Abstract Introduction of doped ceria interlayer to cathode/electrolyte interface of the electrochemical cell with proton conducting electrolyte was investigated using thin Ce0.8Yb0.2O2−δ (YbDC) interlayer of about 500 nm thickness. YbDC interlayer conducted a large amount of protons as much as 170 mA cm−2. It was also found that cathode overpotential of the YbDC interlayer cells consistently showed a plateau at about 400 mV, at which that of the non-interlayer cells did not show, suggesting a possibility that cathode reaction is changed by introducing the doped ceria interlayer. This result also indicates that the interlayer showed high activity for cathode reaction when enough cathodic bias was applied. Especially, the interlayer showed high activity for the improvement of poor cathode reaction between SrZr0.9Y0.1O3−α (SZY-91) electrolyte and platinum cathode.
Keywords Proton conduction; Doped ceria; Cathode interlayer; Electrochemical steam electrolysis
Remark Available online 4 May 2012
Link

Polymorphism and Oxide Ion Migration Pathways in Fluorite-Type Bismuth Vanadate, Bi46V8O89

Authors Xiaojun Kuang, Julia L. Payne, James D. Farrell, Mark R. Johnson, and Ivana Radosavljevic Evans
Source
Chem. Mater.
Volume: 24, Issue: 11, Pages: 2162–2167
Time of Publication: 2012-05
Abstract We report the synthesis, structural characterization, and ionic conductivity measurements for a new polymorph of bismuth vanadate Bi46V8O89, and an ab initio molecular dynamics study of this oxide ion conductor. Structure determination was carried out using synchrotron powder X-ray and neutron diffraction data; it was found that β-Bi46V8O89 crystallizes in space group C2/m and that the key differences between this and the previously reported α-form are the distribution of Bi and V cations and the arrangement of the VO4 coordination polyhedra in structure. β-Bi46V8O89 exhibits good oxide ion conductivity, with σ = 0.01–0.1 S/cm between 600 and 850 C, which is about an order of magnitude higher than yttria stabilized zirconia. The ab initio molecular dynamics simulations suggest that the ion migration pathways include vacancy diffusion through the Bi–O sublattice, as well as the O2– exchanges between the Bi–O and the V–O sublattices, facilitated by the variability of the vanadium coordination environment and the rotational freedom of the VOx coordination polyhedra.
Keywords Oxide ion conductors; bismuth vanadates; X-ray and neutron diffraction; AIMD simulations
Remark Publication Date (Web): May 3, 2012
Link

SrCo1−xSbxO3−δ cathode materials prepared by Pechini method for solid oxide fuel cell applications

Authors Sea-Fue Wang, Hsi-Chuan Lu, Yung-Fu Hsu, Chien-Chung Huang, Chun-Ting Yeh
Source
Ceramics International
Volume: 38, Issue: 7, Pages: 5941–5947
Time of Publication: 2012-09
Abstract In this study, SrCo1−ySbyO3−δ powders were prepared by a modified Pechini method. According to the study results, the cubic Pm3m phase of the SrCo1−ySbyO3−δ ceramics was obtained as 10% of cobalt ions were substituted by antimony ions. Doping of Sb3+ ions appeared both to stabilize the Pm3m phase of the SrCo1−ySbyO3−δ ceramics and to enhance densification and retard grain growth. The coefficient of thermal expansion of the SrCo1−xSbxO3−δ ceramics increased with the content of the antimony ions, ranging from 10.17 to 15.37 ppm/C at temperatures lower than the inflection point (ranging from 450 C to 550 C) and from 22.16 to 29.29 ppm/C at higher temperatures. For the SrCo0.98Sb0.02O3−δ ceramic, electrical conductivity reached a maximum of 507 S/cm at 450 C. The ohmic and polarization resistances of the single cell with the pure SrCo0.98Sb0.02O3−δ cathode at 700 C read respectively 0.298 Ω cm2 and 0.560 Ω cm2. The single cell with the SrCo0.98Sb0.02O3−δ-SDC composite cathode appeared to reduce the impedances with the R0 and RP at 700 C reading respectively 0.109 Ω cm2 and 0.127 Ω cm2. Without microstructure optimization and measured at 700 C, the single cells with the pure SrCo0.98Sb0.02O3−δ cathode and the SrCo0.98Sb0.02O3−δ-SDC composite cathode, demonstrated maximum power densities of 0.100 W/cm2 and 0.487 W/cm2. Apparently, SrCo1−ySbyO3−δ is a potential cathode for use in IT-SOFCs.
Keywords Solid oxide fuel cell; Cathode; Impedance; Cell performance
Remark Available online 19 April 2012
Link

Synthesis, Sintering, Transport Properties, and Surface Exchange of La2Ni0.9Cu0.1O4+δ

Authors Zuoan Li, Truls Norby, Reidar Haugsrud
Source
Journal of the American Ceramic Society
Volume: 95, Issue: 6, Pages: 2065–2073
Time of Publication: 2012-06
Abstract Dense La2Ni0.9Cu0.1O4+δ ceramics were sintered from powders synthesized through a wet-chemical citrate nitrate route with optimized ratios of citrate to nitrate. Less citrate decreases the required sintering temperature and improves the oxygen permeativity. The oxygen permeation was measured as a function of oxygen activity gradient, membrane thickness (0.4–2.6 mm) and temperature (800C–950C). The oxygen self diffusion coefficient DO and the surface exchange coefficient k show Arrhenius-type behaviors with activation energies of ~50 and ~100 kJ/mol, respectively. The oxygen chemical diffusion coefficient Dchem and surface exchange coefficient kchem, measured by conductivity relaxation, exhibit Arrhenius-type behaviors with activation energies of 62 and 104 kJ/mol, respectively. Dchem and kchem are related to DO and k through the thermodynamic factor ωO.
Remark Link

LaCoO3 ceramics obtained from reactive powders

Authors L. Predoana, B. Malic, D. Crisan, N. Dragan, M. Anastasescu, J. Calderon-Moreno, R. Scurtu, M. Zaharescu
Source
Ceramics International
Volume: 38, Issue: 7, Pages: 5433–5443
Time of Publication: 2012-09
Abstract The aim of the present study was to establishing the correlation between the structure and properties of the LaCoO3 powders obtained by aqueous sol–gel method with citric acid and their sintering behavior in order to obtain fully densified ceramics with perovskite structure. Two types of cobalt and lanthanum reagents were used in synthesis, namely nitrates and acetates. The sintering was realized at temperatures ranging between 800 and 1200 C for 2 h. The sintered samples were investigated by classical ceramic methods (shrinkage, density, porosity) and by structural and morphological investigations: XRD, SEM, AFM and XPS. The electrical properties of the samples were determined by impedance spectroscopy. The ceramics obtained with powders starting with acetates have presented a lower sintering ability as compared with the samples obtained from powders starting with nitrates. LaCoO3 ceramics with best properties was obtained from powders starting with nitrates sintered at 1100 C.
Remark Available online 11 April 2012
Link

Preparation and characterization of composite membranes based on sulfonated PEEK and AlPO4 for PEMFCs

Authors Vijay Shankar Rangasamy, Savitha Thayumanasundaram, Niels De Greef, Jin Won Seo, Jean-Pierre Locquet
Source
Solid State Ionics
Volume: 219, Pages: 83–89
Time of Publication: 2012-05
Abstract Sulfonated poly(ether ether ketone) (PEEK) and their composites are considered one of the most promising alternatives for Nafion, the industry benchmark for electrolytic membranes in proton exchange membrane (PEM) fuel cells. In the present study, PEEK was non-homogeneously sulfonated using concentrated H2SO4 at different temperatures (room temperature, 60 C, and 80 C) and time durations (5, 7, 48, and 72 h). Composite membranes of SPEEK with different weight ratios of AlPO4 synthesized by sol–gel were also prepared. Depending on the degree of sulfonation (DS), the Ion Exchange Capacity (IEC) of the membranes varied from 1.06 to 2.9 meq g− 1. XRD results show the increasing amorphous nature of the membranes with increase in IEC and DS value. The water uptake of the membranes also increased with DS. Simultaneous TGA–FTIR measurement of the composite membranes showed better thermal stability compared to pure SPEEK membranes. The water uptake and proton conductivity of the composite SPEEK membranes were found to be lower than that of pure SPEEK membranes, while the composite membranes exhibited a better swelling behavior and mechanical stability than the pure SPEEK samples.
Keywords Proton exchange membrane (PEM); Composite membranes; Sulfonated poly(etheretherketone) (SPEEK); Proton conductivity; Ion exchange capacity (IEC); Sol–gel
Remark Link

Synthesis and electrical properties of a new fluorite-like anionic conductor in the Nd2O3–MoO3 system (43–47 mol% Nd2O3)

Authors V.I. Voronkova, , E.P. Kharitonova, D.A. Belov
Source
Solid State Ionics
Volume: 225, Pages: 654–657
Time of Publication: 2012-10
Abstract This work addresses phase relations in the Nd2O3–MoO3 system (25–50 mol% Nd2O3) and properties of a fluorite-like compound existing in this system in the composition range of 43–47 mol% Nd2O3. We describe for the first time the crystal growth of this compound. The composition of the crystals is Nd10Mo6O33 (Nd2O3:MoO3 = 5:6, 45.5 mol% Nd2O3), which falls within the above composition range. Dielectric spectroscopy data for polycrystalline Nd14Mo8O45 (within the homogeneity range of the fluorite-like compound) suggest a phase transition at 650–700 C. The exact mechanism of the transition remains to be clarified. Nd14Mo8O45 has rather high bulk conductivity, approaching 10− 2 S/cm at 800 C. The low activation energy and key structural features of the compound in question indicate that it is an anionic conductor.
Keywords Fluorite-like compounds; Rare-earth molybdates; Single crystals; Relaxation; Anionic conductor
Remark Available online 22 March 2012
Link

Temperature dependent thermoelectric material power factor measurement system

Authors Jonathan D'Angelo, Adam Downey, Timothy Hogan
Source
Review of scientific instruments
Volume: 81, Issue: 075107 Publisher: American Institute of Physics, Time of Publication: 2010-06
Abstract Thermoelectric materials can be used for cooling/heating applications, or converting waste heat into electricity. Novel thermoelectric materials have been discovered in recent years. Characterization of an electrical conductivity and thermopower of a sample from room temperature to ≥ 900 K is often necessary for thermoelectric materials. This paper describes a system built for measurement of the power factor of thermoelectric materials from 300 to 1273 K. Characterization results of the system are also presented.

High temperature electronic properties of BaTiO3 – Bi(Zn1/2Ti1/2)O3 – BiInO3 for capacitor applications

Author Natthaphon Raengthon and David P. Cann
Source
Journal of Electroceramics
Volume: 28, Issue: 2-3, Pages: 165-171
Time of Publication: 2012-03
Abstract Solid solutions xBaTiO3 – (1-x)(0.5Bi(Zn1/2Ti1/2)O3 – 0.5BiInO3), where x = 0.95–0.60, were prepared by conventional mixed oxide method. The single phase perovskite structure was obtained for the composition with x ≥ 0.75. Phase transformation from tetragonal to pseudocubic was observed from x-ray diffraction patterns when x decreased from 0.95 to 0.75. In tetragonal phase region, x ≥ 0.90, the increase of Bi(Zn1/2Ti1/2)O3 – BiInO3 content decreased the tetragonality and the temperature at which the relative permittivity is maximum (Tmax). The increase in lattice parameter and Tmax were observed in the pseudocubic phase region, x < 0.90. Additionally, a highly broad and diffuse phase transition was observed from the dielectric data in the pseudocubic phase region. The introduction of Ba vacancies in compositions with x = 0.80 and 0.75 also improved dielectric loss at high temperatures. The incorporation of BiInO3 into the BaTiO3 – Bi(Zn1/2Ti1/2)O3 compound was also found to improve the temperature coefficient of the relative permittivity, with values as low as approximately −1,000 ppm/K. Overall, ternary perovskite solid solutions based on adding Bi(Zn1/2Ti1/2)O3 – BiInO3 to BaTiO3 shows excellent potential for high temperature capacitor applications
Keywords High temperature capacitor – Bi-based perovskite – BiInO3 – Bi(Zn1/2Ti1/2)O3 – BaTiO3 – Insulation resistance
Remark Link

Stability of (Ln0.8Ca0.1Ln′0.1)2Ti2O7−δ (Ln=Dy, Yb; Ln′=Ce, Tb) and (Tb0.9Ca0.1)2Ti2O7−δ pyrochlores under redox conditions

Authors S.N. Savvin, A.V. Shlyakhtina, D.A. Belov, J.C. Ruiz-Morales, L.G. Shcherbakova, P. Nuez
Source
Solid State Ionics
Volume: 225, Pages: 457–463
Time of Publication: 2012-10
Abstract The stability of (Ln0.8Ca0.1Ln′0.1)2Ti2O7−δ (Ln=Dy, Yb; Ln′=Ce, Tb) pyrochlores under different redox conditions (air, dry and wet H2) has been studied. The bulk conductivity of the terbium-containing materials is slightly higher under reducing conditions (5% H2 + 95% Ar) than in air, reaching ~ 6 10− 2 and 2.5 10− 2 S/cm at 800 C for (Yb0.8Ca0.1Tb0.1)2Ti2O7−δ and (Dy0.8Ca0.1Tb0.1)2Ti2O7−δ, respectively. In air–hydrogen–air cycles, the bulk conductivity returns to its original level in air: ~ 2 10− 2 and 1 10− 2 S/cm at 800 C in (Yb0.8Ca0.1Tb0.1)2Ti2O7−δ and (Dy0.8Ca0.1Tb0.1)2Ti2O7−δ, respectively. Exposure of (Dy0.8Ca0.1Tb0.1)2Ti2O7−δ to a flowing mixture of 5% H2 and 95% Ar for 100 h slightly reduces its conductivity: from 0.029 to 0.023 S/cm at 900 C. The cerium-containing materials (Yb0.8Ca0.1Ce0.1)2Ti2O7−δ and (Dy0.8Ca0.1Ce0.1)2Ti2O7−δ were found to be unstable under reducing conditions. The bulk conductivity of (Yb0.8Ca0.1Ce0.1)2Ti2O7−δ is practically independent on the atmosphere while the grain boundary conductivity increased from 5.6 10− 8 in air to ~ 1 10− 5 S/cm at 425 C on reducing the sample in 5%H2–Ar gas mixture. However, after two redox cycles air–5%H2–Ar–air the sintered pellet of (Yb0.8Ca0.1Ce0.1)2Ti2O7−δ fractured whereas (Dy0.8Ca0.1Ce0.1)2Ti2O7−δ degraded immediately under reducing conditions. It was observed that the size mismatch between Ln and Ln´ cations strongly affects the bulk to grain boundary conductivity ratio in (Ln0.8Ca0.1Ln′0.1)2Ti2O7−δ (Ln=Dy, Yb; Ln′=Ce, Tb) pyrochlores.
Keywords Pyrochlore; Donor doping; High-temperature conductivity; Ionic conductivity; Solid electrolyte; Electronic conductivity
Remark Available online 8 March 2012; http://dx.doi.org/10.1016/j.ssi.2012.02.009
Link

Spark Plasma Sintering and Hot Pressing of Hetero-Doped LaNbO4

Authors Guttorm E. Syvertsen, Claude Estourns, Harald Fjeld, Reidar Haugsrud, Mari-Ann Einarsrud, Tor Grande
Source
Journal of the American Ceramic Society
Volume: 95, Issue: 5, Pages: 1563–1571
Time of Publication: 2012-05
Abstract LaNbO4/La3NbO7 and LaNbO4/LaNb3O9 cer-cer composites were prepared by impregnating Ca-doped LaNbO4 powder, synthesized by spray pyrolysis, with La- or Nb-precursor solutions. The sintering of the calcined powders was investigated by dilatometry, and dense composites were prepared by conventional sintering, hot pressing, and spark plasma sintering. The particle size of the starting powders was about 50 nm, and the average grain size of the dense materials ranged from 100 nm and upwards, depending on the sintering temperature, sintering procedure, and the phase composition. The unit cell parameters of LaNbO4 showed a finite size effect and approached the cell parameters of tetragonal LaNbO4 with decreasing crystallite size, both for the single-phase material and the composites. The minority phase (La3NbO7 or LaNb3O9) were observed as isolated grains and accumulated at triple points and not along the grain boundaries, pointing to a large dihedral angle between the phases. The calcium-solubility in the minority phases was larger than in LaNbO4, which corresponds well with previous reports. The electrical conductivity of the hetero-doped materials was similar to, or lower than, that for Ca-doped LaNbO4.
Remark Link

Sandvik Sanergy HT – A potential interconnect material for LaNbO4-based proton ceramic fuel cells

Authors Anders Werner Bredvei Skilbred, Reidar Haugsrud
Source
Journal of Power Sources
Volume: 206, Pages: 70–76
Time of Publication: 2012-05
Abstract High temperature properties of Sandvik Sanergy HT have been studied to evaluate the alloy's suitability as an interconnect material for LaNbO4 based proton ceramic fuel cells (PCFCs). The thermal expansion behavior of the alloy deviates from LaNbO4 at higher temperatures which may be unfavorable, however the average values for the two materials over the whole temperature region are rather similar. The oxidation kinetics was parabolic and the rate constants were low at temperatures below 1000 C. Accelerated oxidation was encountered after 300 h at 1000 C revealing that the material may undergo severe degradation at sufficiently high temperatures. A complex oxide scale containing an inner layer of chromium oxide and an outer layer of various spinel phases containing chromium, manganese and iron was formed at all temperatures. As a consequence of high oxidation resistance and an oxide with relatively high electronic conductivity, the area specific resistance (ASR) of Sandvik Sanergy HT measured at 700 C proved to be low.
Keywords Proton ceramic fuel cell; Interconnect; Sandvik Sanergy HT; Oxidation kinetics; Thermal expansion; Area specific resistance
Remark Link

A novel perovskite-based proton conductor for solid oxide fuel cells

Authors Ramya Hariharan, T.R.S. Prasanna, Prakash Gopalan
Source
Scripta Materialia
Volume: 66, Issue: 9, Pages: 658–661
Time of Publication: 2012-05
Abstract A perovskite-based electrolyte, Ca-substituted YAlO3, has been synthesized by the citrate gel process. The conductivity of Y0.9Ca0.1AlO3-δ has been studied by AC impedance spectroscopy in controlled atmospheres in the temperature range 300–800 C. The material has been found to be a mixed conductor with dominant p-type electronic conduction at elevated temperatures and a combined protonic conduction below 600 C in wet conditions. The H/D isotope effect on conductivity confirms the presence of protonic conductivity between 400 and 600 C.
Keywords Proton conduction; Electrical properties; Solid electrolyte; Perovskite oxide; Fuel cell materials
Remark Link

50 mol% indium substituted BaTiO3: Characterization of structure and conductivity

Authors S.M.H. Rahman, C.S. Knee, I. Ahmed, S.G. Eriksson, R. Haugsrud
Source
International Journal of Hydrogen Energy
Volume: 37, Issue: 9, Pages: 7975–7982
Time of Publication: 2012-05
Abstract BaTi0.5In0.5O3−δ was prepared by solid state reaction at 1400 C. Rietveld analysis of high resolution X-ray powder diffraction data indicated phase pure as-prepared material that adopts a cubic perovskite structure with a = 4.1536(1) . Thermogravimetric analysis revealed the presence of significant levels of protons in the as-prepared material and 57% of the theoretically achievable protonation was attained on exposure to a humid environment at 185 C. After hydration the cell parameter increased to 4.1623(1) . Electrical conductivity was measured both with fixed and variable frequency ac impedance methods as a function of temperature, oxygen-, water vapour- and heavy water vapour partial pressures. In the temperature range 400–800 C a slight increase in the total conductivity with increasing oxygen partial pressure is encountered, characteristic of a contribution from p-type charge carriers. The effect of the water vapour pressure on conductivity below 600 C is much more prominent indicative of dominant proton conduction. At 300 C the total conductivity in wet O2 was estimated to be 9.30 10−5 S/cm. At T > 800 C the material is a pure oxide ion conductor.
Keywords Barium titanate; Perovskite; Brownmillerite; Proton conductivity; X-ray diffraction; Impedance spectroscopy
Remark Link

Ion mobility, phase transitions, and conductivity of crystal phases in KF-CsF-SbF3-H2O system according to data of NMR and impedance spectroscopy

Authors V. Ya. Kavun, L. A. Zemnukhova, A. I. Ryabov, A. B. Podgorbunskii, S. V. Gnedenkov, S. L. Sinebryukhov and V. I. Sergienko
Source
Russian Journal of Electrochemistry
Volume: 48, Issue: 1, Pages: 104-110
Time of Publication: 2012-01
Abstract The methods of NMR, thermogravimetric analysis, and impedance spectroscopy were used to study ion mobility, phase transitions, and ion conductivity in crystal phases in the KF-CsF-SbF3-H2O system. Analysis of 19F NMR spectra allowed tracing the dynamics of ion movement in the fluoride sublattice under temperature variations, determining their types and temperature ranges, in which they are implemented. The observed phase transitions in potassium-cesium fluoroantimonates(III) are phase transitions to the superionic state. It is found that the predominant form of ion movement in the high-temperature modifications formed as a result of phase transitions becomes diffusion of fluoride ions. According to the results of electrophysical studies the K1−xCsx SbF4 (x ≤ 0.2) high-temperature phases are superionic. Their conductivity reaches the values of ∼10−2 to 10−3 S/cm at 463–483 K. The high-temperature phases are stabilized under cooling, which results in a significant increase in conductivity at the room temperature.
Keywords potassium-cesium tetrafluoroantimonates(III) – ion mobility – phase transitions – conductivity – NMR spectra
Remark DOI: 10.1134/S1023193512010090
Link

Defect structure and its nomenclature for mixed conducting lanthanum tungstates La28–xW4+xO54+3x/2

Authors Skjalg Erdal, Liv-Elisif Kalland, Ragnhild Hancke, Jonathan Polfus, Reidar Haugsrud, Truls Norby, Anna Magras
Source
International Journal of Hydrogen Energy
Volume: 37, Issue: 9, Pages: 8051–8055
Time of Publication: 2012-05
Abstract Based on results from experimental and theoretical studies of the crystal structure of lanthanumtungstateView the MathML source, we present a defect model comprising an inherently disordered and partially occupied oxide ion sublattice, which rationalizes hydration and ionic conduction of the materials in the undoped state. Applying the model to experimental conductivity data enables extraction of defect thermodynamics and transport parameters of protons, oxide ions and electronic defects. The standard enthalpy and entropy changes of the hydration of inherent oxygen vacancies are estimated to be −83 kJ/mol and −125 J/mol K (per mole of H2O), respectively.
Keywords Lanthanum tungstate; Defect structure; Inherent disorder; Partial occupancy; Mixed conductor
Remark Link

The role of B-site cations on proton conductivity in double perovskite oxides La2MgTiO6 and La2MgZrO6

Authors Camilla K. Vigen, Tor Svendsen Bjrheim, Reidar Haugsrud
Source
International Journal of Hydrogen Energy
Volume: 37, Issue: 9, Pages: 7983–7994
Time of Publication: 2012-05
Abstract Acceptor-doped La2MgTiO6 (LMTO) and La2MgZrO6 (LMZO) have been investigated to contribute to clarify the role of the B-site cations in A2B′B″O6 double perovskite oxides on formation and mobility of protons. Thermogravimetry and a.c. conductivity measurements in the temperature range 1000-300 C, as well as DFT-calculations of LMTO, have been the basis for evaluating hydration thermodynamics and transport parameters of the materials. Both compounds show exothermic hydration of oxygen vacancies, but low concentrations of protons. The proton transport is limited by relatively high activation energies of mobility; 0.84 eV and 0.78 eV for LMTO and LMZO, respectively. This is suggested to reflect association to effectively negative charged defects formed by site exchange among the B-site cations. Consequently, the maximum proton conductivity of LMTO and LMZO is in the order of 10−5 S/cm.
Keywords Double perovskite; La2MgTiO6; La2MgZrO6; Proton mobility; Hydration thermodynamics
Remark Link

Influence of Microwave-Assisted Pechini Method on La0.80Sr0.20Ga0.83Mg0.17O3–δ Ionic Conductivity

Authors S. Boldrini, C. Mortal, S. Fasolin, F. Agresti, L. Doubova, M. Fabrizio, and S. Barison
Source
Fuel Cells
Volume: 12, Issue: 1, Pages: 54–60
Time of Publication: 2012-02
Abstract With the aim of investigating the microwave influence on the electrolyte material properties, La0.80Sr0.20Ga0.83Mg0.17O2.815 was prepared by both a conventional and a microwave-assisted sol–gel Pechini method. With respect to the conventional Pechini method (hereafter SGP), the microwave assisted process (hereafter MWA-SGP) guaranteed a faster procedure, reducing the time needed to remove the excess solvents to complete the polyesterification reaction from some days to a few hours. In fact, when a MWA-SGP method was used, powders having higher phase purity were obtained. The sintering process at 1,450 C of the powders prepared by both methods yielded pellets with similar density values (≥92% of theoretical). Nevertheless, only by microwave-assisted process single-phase products were obtained and no secondary phases such as tetragonal LaSrGaO4 and LaSrGa3O7 were detected. These by-products have been demonstrated to be detrimental for conductivity. Indeed, pellets obtained by MWA-SGP method showed oxygen ionic conductivity values higher (about 30–40%) than those checked for SGP samples, thus demonstrating the important role of the microwave process on reducing time and costs and on improving the electrolyte properties.
Keywords Ionic Conductivity;IT-SOFC;Microwave Processing;(Sr, Mg)-Doped LaGaO3;Sol–Gel
Remark Link

Impact of Parylene-A Encapsulation on ZnO Nanobridge Sensors and Sensitivity Enhancement via Continuous Ultraviolet Illumination

Authors C.-C. Huang, A.D. Mason, J.F. Conley, C. Heist, M.T. Koesdjojo, V.T. Remcho and T. Afentakis
Source
Journal of Electronic Materials
Volume: 41, Issue: 5, Pages: 873-880
Time of Publication: 2012-05
Abstract The impact of parylene-A encapsulation and the effect of continuous ultraviolet (UV) exposure on ZnO nanobridge sensor response are investigated. ZnO nanowire (NW) devices are fabricated using a novel method that involves selective growth of ZnO nanobridges between lithographically defined pads of carbonized photoresist (C-PR). We find that a thin coating of parylene-A effectively attenuates the response of NW devices to O2, H2O vapor, and UV illumination. The accessibility of the amine group on parylene-A for chemical functionalization is verified by transforming the amine groups on the surface of the parylene-A coating into aromatic imine groups, followed by UV–Vis absorption. Our results suggest that, in addition to modulating environmental sensitivity and providing protection of the ZnO NWs for liquid- and vapor-phase sensing, the parylene-A encapsulation may also serve as an activation layer for further specific functionalization targeting selective sensing. We also found that the sensitivity and response time of ZnO nanobridge devices to O2 are dramatically improved by continuously exposing the nanobridge devices to UV illumination. Finally, we show that the C-PR directed growth method can also be used to isolate free-standing NW carpet.
Keywords ZnO – nanowire – parylene – CVD – nanobridge – sensor – functionalization – directed integration
Remark Link

On the hydration of grain boundaries and bulk of proton conducting BaZr0.7Pr0.2Y0.1O3-δ

Authors Kristine Bakkemo Kostl, Anna Magras, Truls Norby
Source
International Journal of Hydrogen Energy
Volume: 37, Issue: 9, Pages: 7970–7974
Time of Publication: 2011-12
Abstract We report here for the first time bulk and grain boundary conductivities from impedance spectra of a ceramic proton conductor (BaZr0.7Pr0.2Y0.1O3-δ) taken during hydration and H/D isotope exchange transients (at 400 C). The results suggest that water moves quickly along grain boundary cores, and then interact from there with the space charge layers and, in turn, grain interiors. Hydration and H/D isotope exchange have simple monotonic effects on the bulk conductivity in line with what is expected from it being dominated by protons. The transients for grain boundary conductivity exhibit however hysteresis: During hydration, the core charge and grain boundary resistance appear to go through transient minima related to non-equilibrium distributions of defects between the core and grain interior – notably because protons diffuse faster than oxygen vacancies between the grain boundary and grain interior. At equilibrium, hydration increases the core charge and the depletion of positive charge carriers in the space charge layers. During H/D isotope exchange relatively fast hysteretic transients indicate that the space charge layers experience changes in charge carrier (D+ vs. H+) mobility as well as in D2O vs. H2O hydration thermodynamics.
Keywords BaZrO3, Pr-substituted, acceptor-doped; BaZr0.7Pr0.2Y0.1O3-δ; Proton conductivity; Grain boundaries, space charge layer; Hydration; Impedance spectroscopy
Remark Link

Synthesis, structural and electrical properties of double perovskite Sr2NiMoO6 ceramics

Authors A. Prasatkhetragarn, S. Kaowphong and R. Yimnirun
Source
Applied Physics A: Materials Science & Processing
Volume: 107, Issue: 1, Pages: 117-121
Time of Publication: 2012-01
Abstract The double perovskite Sr2NiMoO6 powders and ceramics were prepared by two different (conventional and precursor) solid-state reaction methods. The phase structure was characterized by XRD and TEM techniques. It has been indicated that single-phase perovskite powders were obtained when calcined in air at 1300C. However, nano-particles of the size 30–60 nm have been found in powders prepared with the precursor method, while those from the conventional route exhibit large irregular shaped particles with aggregation. The dielectric properties (ε r and tanδ) were also examined in the sintered ceramics. The results showed the transition point at 280C for conventional route, while no clear phase change was observed in ceramics from the precursor route. These observations clearly indicate that the different starting processes affected the phase formation behavior and the electrical properties of Sr2NiMoO6 ceramics.
Remark Link

Dielectric Relaxation in BaTiO3–Bi(Zn1/2Ti1/2)O3 Ceramics

Authors Natthaphon Raengthon, David P. Cann
Source
Journal of the American Ceramic Society
Volume: 95, Issue: 5, Pages: 1604–1612
Time of Publication: 2012-05
Abstract A dramatic improvement in the dielectric and electrical properties has been observed in ceramics of 0.8BaTiO3–0.2Bi(Zn1/2Ti1/2)O3 through the introduction of Ba vacancies. It possesses a high relative permittivity (εr > 1150) along with a low dielectric loss (tan δ < 0.05) that is maintained up to temperatures as high as 460C. It is also characterized by a high resistivity of 70 GΩ-cm, which remains constant up to 270C. Analysis of complex impedance (Z*) and complex electric modulus (M*) data, measured over the frequency range of 1–106 Hz, revealed a number of important findings. At high temperatures (T > 255C), a complex plane analysis of Z″ versus Z′ and the frequency dependence of Z″ suggests an electrically inhomogeneous microstructure for the stoichiometric composition. The stoichiometric composition exhibited activation energies of ~1 eV which suggests an extrinsic conduction mechanism. However, the introduction of Ba vacancies resulted in electrically homogeneous microstructure. An overlap of the Z″ and M″ peaks in the frequency domain and much larger activation energies were observed, on the order of half of the band gap, suggesting an intrinsic conduction mechanism. A more detailed analysis of the data reveals insights into the physical mechanisms underpinning the dielectric and ac conductivity.
Remark Link

Fabrication and electrochemical properties of cathode-supported solid oxide fuel cells via slurry spin coating

Authors Min Chen, Jing-Li Luo, Karl T. Chuang, Alan R. Sanger
Source
Electrochimica Acta
Volume: 63, Pages: 277–286
Time of Publication: 2012-02
Abstract A cathode-supported SOFC consisting of LSM (La0.8Sr0.2MnO3-δ) cathode supporter, LSM-Sm0.2Ce0.8O2-δ (SDC) cathode functional layer (CFL), yttria stabilized zirconia (YSZ)/SDC bi-layered electrolyte and Ni-YSZ anode layer was fabricated by a slurry spin coating technique. The influence of the porosity in both the CFL and cathode supporter on the electrochemical properties of the cells has been investigated. It was found that properly controlling the porosity in the CFL would improve the performance of the cells using O2 in the cathode side (O2-cells), with a maximum power density (MPD) value achieving as high as 0.58 W•cm−2 at 850 C. However, this improvement is not so evident for the cells using air in the cathode side (air-cells). When increasing the porosity in the cathode-supporter, a significant increase of the power density for the air cells due to the decreasing Rconc,c(concentration polarization to the cell resistance) can be ascertained. In terms of our analysis on various electrochemical parameters, the Ract (activation polarization to the cell resistance) is assumed to be mainly responsible for the impedance arcs measured under the OCV condition, with a negligible Rconc,cvalue being able to be detected in our impedances. In this case, a significant decreasing size of the impedance arcs due to the increasing porosity in the cathode supporter would correspond to a decrease of the Ract values, which was proved to be induced by the decreasingRconc,c.
Keywords Slurry spin coating; Cathode-supported SOFC; Concentration polarization; Activation polarization; Power density
Remark Link

The effect of cation non-stoichiometry in LaNbO4 materials

Authors Guttorm E. Syvertsen, Anna Magras, Reidar Haugsrud, Mari-Ann Einarsrud, Tor Grande
Source
International Journal of Hydrogen Energy
Volume: 37, Issue: 9, Pages: 8017–8026
Time of Publication: 2012-05
Abstract The effect of cation non-stoichiometry in LaNbO4 was investigated by impregnating nano-crystalline LaNbO4 with small amounts of La3+, Nb5+ and Ca2+ oxide precursors. The sintering properties of the modified LaNbO4 powders were investigated by dilatometry, and the microstructure and phase composition were studied by electron microscopy and X-ray diffraction. The electrical properties of the materials were studied by 4-point DC-conductivity and 2-point 4-wire AC-conductivity at elevated temperatures in controlled atmosphere. Minor variations in the cation stoichiometry were shown to have a pronounced effect on both the sintering properties as well as the electrical conductivity. Addition of CaO, which introduced secondary phases above 0.25 mol% CaO, increased the sintering temperature and improved the conductivity of the materials. La2O3- and Nb2O5-excess materials did not show large variation in the electrical conductivity relative to pure LaNbO4, while the sintering properties were strongly affected by the nominal La/Nb ratio in LaNbO4. The present findings demonstrate the sensitivity of cation non-stoichiometry in materials with limited solid solubility.
Keywords LaNbO4; Proton conductivity; Phase purity; Solid solubility
Remark Link

Effects of surface coatings on the determination of Dchem and kchem in La2NiO4+δ by conductivity relaxation

Authors Zuoan Li, Reidar Haugsrud
Source
Solid State Ionics
Volume: 206, Pages: 67-71
Time of Publication: 2012-01
Abstract In this work, we utilize surface modification to accurately determine oxygen diffusivity and surface exchange in La2NiO4 + δ by transient conductivity. To achieve ‘instantaneous’ gas exchange in the reaction cell, a total pressure change was adopted instead of exchange of gas mixtures at 1 atm. Conductivity relaxation measurements were performed in the temperature range of 600–900 C and at oxygen partial pressures of 0.2, 1.0 and 1.9 atm. Due to the large uncertainties associated with deriving oxygen chemical diffusion and surface coefficients simultaneously, we limited the relaxation to pure bulk diffusion control by coating nano-grained La2NiO4 + δ particles on the sample surface. After determining Dchem, kchem was derived by fitting the relaxation data of the uncoated sample. The transient experiments via both oxidation (a step change of pO2 from 0.2 to 1.0 atm) and reduction (1.9 to 1.0 atm) give consistent results of Dchem and kchem showing Arrhenius-type behaviour with activation energies of ~ 90 kJ/mol and ~ 150 kJ/mol, respectively.
Keywords Conductivity relaxation; Surface modification; Surface exchange; Oxygen diffusion; La2NiO4 + δ
Remark Link

Hydration and proton conductivity in LaAsO4

Authors Tor S. Bjrheim, Truls Norby and Reidar Haugsrud
Source
Journal of Materials Chemistry
Volume: 22, Issue: 4, Pages: 1652-1661
Time of Publication: 2012-04
Abstract Incorporation and transport of protonic defects have been studied in nominally undoped and 1 and 3 mol% Sr-doped LaAsO4 prepared by a co-precipitation route. AC impedance of the materials was measured as a function of temperature (1150 to 400 C), pO2 (1 to 1 10−5 atm) and pH2O (0.025 to 3 10−5 atm). The bulk conductivities generally decrease with decreasing temperature and moreover with decreasing pH2O within the whole temperature range. At the highest temperatures, a small decrease in the conductivity with decreasing pO2 was also observed. The defect structure of Sr-doped LaAsO4 appears to be dominated by oxygen vacancies in the form of pyroarsenate ions, As2O4−7, in dry atmospheres at high temperatures and by protonic defects in the form of hydrogen arsenate ions, HAsO2−4, in wet atmospheres. A significant isotope effect shows that protons contribute to the total conductivity at all temperatures under wet conditions and predominate at temperatures below [similar]850 C. The remaining contributions are attributed to oxide ions and electron holes. The extracted hydration thermodynamics are comparable to those determined for other LnXO4 (X = P, V, Nb, Ta) compounds, and the enthalpy of mobility of protons (86 5 and 88 5 kJ mol−1 for the 1 and 3 mol% doped samples, respectively) follows an apparent trend for the isostructural LaXO4 (X = P, As, V) series with the enthalpy of mobility of protons decreasing with increasing radius of the X-site cation. However, the partial proton conductivities of Sr-doped LaAsO4 are lower than those determined for acceptor doped LaPO4 and LaVO4 for which the possible reasons are discussed.
Remark Link

Evaluation of the electrode/electrolyte contact quality in solid oxide fuel cells

Authors Jacqueline Amanda Figueiredo dos Santos, Michel Kleitz, Tulio Matencio, Rosana Zacarias Domingues
Source
Electrochimica Acta
Volume: 60, Pages: 224–229
Time of Publication: 2012-01
Abstract Symmetrical cells have been prepared by depositing suspensions with different active powder concentrations (50% and 60% by weight respectively) of lanthanum strontium cobalt iron oxide (La0.6Sr0.4Co0.2Fe0.8O3-δ) on identical yttria stabilized zirconia pellets (LSCF/YSZ/LSCF). Their impedance characteristics are compared to that of a symmetrical cell with platinum electrodes deposited on a similar zirconia pellet (Pt/YSZ/Pt). The LSCF cells show different values of the electrolyte resistance. Referring to the electrolyte resistance obtained with the Pt cell and assuming that this value corresponds to almost perfect electrode/electrolyte contacts, it is possible to estimate the Effective Conducting Area (ECA) of the electrodes. The use of the ECA parameter allows a better comparison of the electrode polarizations.
Keywords solid oxide fuel cells; porous electrodes; cathode
Remark Link

Influence of Pr substitution on defects, transport, and grain boundary properties of acceptor-doped BaZrO3

Authors Anna Magras, Christian Kjlseth, Reidar Haugsrud, Truls Norby
Source
International Journal of Hydrogen Energy
Volume: 37, Issue: 9, Pages: 7962–7969
Time of Publication: 2012-05
Abstract We report on effects of partially substituting Zr with the multivalent Pr on the conductivity characteristics of acceptor (Gd) doped BaZrO3-based materials. BaZr0.6Pr0.3Gd0.1O3−δ was sintered 96% dense at 1550 C with grains of 1–4 μm. The electrical conductivity was characterised by impedance spectroscopy and EMF transport number measurements as a function of temperature and the partial pressures of oxygen and water vapour. H2O/D2O exchanges were applied to further verify proton conduction. The material is mainly a mixed proton–electron conductor: the p-type electronic conductivity is ∼0.004 and ∼0.05 S/cm in wet O2 at 500 and 900 C, respectively, while the protonic conductivity is ∼10−4 S/cm and ∼10−3 S/cm. The material is expectedly a pure proton conductor at sufficiently low temperatures and wet conditions. The specific grain boundary conductivity is essentially equal for the material with or without Pr, but the overall resistance is significantly lower for the former. We propose that replacing Pr on the Zr site reduces the grain boundary contribution due to an increased grain size after otherwise equal sintering conditions.
Keywords BaZrO3; BaPrO3; Defects and transport; Grain boundaries; Grain boundary specific conductivity
Remark Link

Effects of A and B site acceptor doping on hydration and proton mobility of LaNbO4

Authors Morten Huse, Truls Norby, and Reidar Haugsrud
Source
International Journal of Hydrogen Energy
Volume: 37, Issue: 9, Pages: 8004–8016
Time of Publication: 2012-05
Abstract Acceptor doping of the high temperature proton conductor LaNbO4 has been studied by impedance spectroscopy in various atmospheres at 300–1100 C and by X-ray powder diffraction and scanning electron microscopy. Doping LaNbO4 on both A and B site (with Ca and Ti, respectively) resulted in a two-phase composition of LaNbO4 and LaNb3O9. This composite is interesting as the two phases make it a mixed proton and electron conductor. The electrical characterisation of Ti-doped LaNbO4 revealed mixed electronic (n- and p-type) and ionic conductivity at temperatures above approx. 750 C, while proton conductivity was dominating below this temperature under wet conditions. Ti-doping resulted in higher activation enthalpy and lower mobility of protons as compared to Ca-doping, attributed to stronger proton–acceptor association in the former case. Thermodynamic constants for hydration of associated protons and proton–acceptor association as well as mobility parameters were fitted to the experimental data and came out as , , , and , and . Neither B site doping nor A and B site co-doping showed indications of increased solubility relative to sole A site doping in LaNbO4.
Keywords LaNbO4; Ti-doped LaNbO4; Defect association; Proton mobility; Proton conductivity; Hydration thermodynamics
Remark Link

Effects of (LaSr)(CoFeCu)O3-δ Cathodes on the Characteristics of Intermediate Temperature Solid Oxide Fuel Cells

Authors Sea-Fue Wang, Chun-Ting Yeh, Yuh-Ruey Wang, Yung-Fu Hsu
Source
Journal of Power Sources
Volume: 201, Pages: 18–25
Time of Publication: 2012-03
Abstract In this study, Cu2+ ions doped La0.6Sr0.4Co0.2Fe0.8O3−δ cathodes are prepared for use in solid oxide fuel cells (SOFCs). The maximum electrical conductivities of the La0.6Sr0.4Co0.2Fe0.7Cu0.1O3−δ (438 S cm−1) and the La0.6Sr0.4Co0.1Fe0.8Cu0.1O3−δ (340 S cm−1) discs are higher than that of the La0.6Sr0.4Co0.2Fe0.8O3−δ disc (LSCF; 81 S cm−1) sintered at 1100 C. The substitution of Cu2+ over Fe3+ leads to a higher coefficients of thermal expansion (CTE), while the replacement of Co3+ by Cu2+ results in a lower CTE. Single cells with the La0.6Sr0.4Co0.2Fe0.8O3−δ, La0.6Sr0.4Co0.2Fe0.7Cu0.1O3−δ, and La0.6Sr0.4Co0.1Fe0.8Cu0.1O3−δ cathodes operating at 650 C and 550 C show similar ohmic resistance (R0) values while the polarization resistance (RP) values of the cells with the La0.6Sr0.4Co0.2Fe0.7Cu0.1O3−δ and a0.6Sr0.4Co0.1Fe0.8Cu0.1O3−δ cathodes are slightly lower than that of the single cell with the La0.6Sr0.4Co0.2Fe0.8O3−δ cathode, indicating that the Cu2+-doped LSCF cathode exhibits a greater electrochemical catalytic activity for oxygen reduction. Maximum power densities of the cells with the La0.6Sr0.4Co0.2Fe0.8O3−δ, La0.6Sr0.4Co0.2Fe0.7Cu0.1O3−δ, and La0.6Sr0.4Co0.1Fe0.8Cu0.1O3−δ cathodes operating at 700 C read respectively 1.07, 1.15, and 1.24 W cm−2. It is evident that the doping of Cu2+ ions in LSCF is beneficial to the electrochemical performance of the cells.
Keywords Solid oxide fuel cell; cathode; cathode; impedance; Cell performance
Remark Link

Synthesis and Enhanced Proton Conduction in a 20 mol% Ytterbium Doped Barium Zirconate Ceramic Using Zn as Sintering Aid

Authors Seikh M.H. Rahman, Istaq Ahmed, Sten G. Eriksson
Source
Applied Mechanics and Materials
Mechanical and Aerospace Engineering
Volume: 110-116 Time of Publication: 2011-10
Abstract 20% Ytterbium (III)-doped perovskite structured barium zirconate, BaZrO3, was prepared by two different synthesis routes: solid state and sol-gel routes. 2 % Zinc (II) was added as an acceptor dopant at the Zr (IV) site according to stoichiometry. It was also added as 2 % excess of the formula. The purpose of this study is to see how zinc (II) acts as a sintering aid in view of synthesis route, densification and conductivity of the material. A dense ceramic (90% of theoretical density) was achieved by the sol-gel method when stoichiometry was adjusted. Phase purity of the samples was checked by X-ray powder diffraction (XRD). Thermogravimetric analysis (TGA) and Impedance spectroscopy (IS) was used to characterize hydration and electrical conductivity respectively.The data shows that the addition of stoichiometric amounts of Zn2+ via sol-gel synthesis route promotes not only densification but also water incorporation and conductivity in comparison with the solid state route, keeping the same final sintering temperature of 1500C. For example, pre-hydrated BaZr0.78Zn0.02Yb0.2O3-δ, prepared via the sol-gel method shows total conductivity (σtot) value of 3.14*10-5 and 3.8*10-3 Scm-1, whereas for the solid state route, σtot values are 1.74*10-5 and 8.87*10-4 Scm-1 under dry Ar (heating cycle) at 300 C and 600 C, respectively.
Keywords BaZrO3, Impedance Spectroscopy, Proton Conductivity, Sintering Aid, TGA, X-Ray Diffraction (XRD)
Editor Wu Fan
Remark Online since October, 2011; DOI 10.4028/www.scientific.net/AMM.110-116.1181
Link

Effect of nano-grain size on the ionic conductivity of spark plasma sintered 8YSZ electrolyte

Authors K. Rajeswari, M. Buchi Suresh, Dibyendu Chakravarty, Dibakar Das, Roy Johnson
Source
International Journal of Hydrogen Energy
Volume: 37, Issue: 1, Pages: 511–517
Time of Publication: 2012-01
Abstract Densification and micro-structural development of ultra fine 8 mol% yttria stabilized zirconia (8YSZ) nano powder were investigated systematically by varying the SPS sintering temperature at constant applied pressure of 50 MPa. A hundred fold decrease in average grain size ranging from 10 μm to 80 nm is observed on decreasing the SPS sintering temperature from 1200 C to 1050 C with >99% of theoretical densities. Impedance measurements on the samples indicated an enhancement in the ionic conductivity at 700 C from 0.004 S/cm to 0.018 S/cm with decrease in grain size from 10 μm to 0.51 μm and a significant increase in conductivity from 0.018 S/cm to 0.068 S/cm on further reduction of grain size to 80 nm. A significant change in the grain-boundary conductivity is noticed on reducing the grain sizes to nano regime. The diverse microstructure with ultra fine grain size resulting from SPS at 1050 C could contribute to the enhanced ionic conductivity, which is supported by the activation energy data.
Keywords Solid oxide fuel cells; Electrolyte; Microstructure; Spark plasma sintering
Remark Link

Dielectric relaxation in a thermosetting polyimide modified with a thermoplastic polyimide

Authors D. A. Belov, S. Yu. Stefanovich and M. Yu. Yablokova
Source
Polymer Science Series A
Volume: 53, Issue: 10, Pages: 963-967
Time of Publication: 2011-10
Abstract Relaxation processes in glass-fiber-reinforced composites with a polymer matrix based on blends of thermosetting and thermoplastic polyimides are studied via dielectric-relaxation spectroscopy. For all investigated blends, two relaxation processes related to the β relaxation of different fragments of the polymer chain are found. Linear flexiblechain polyimide incorporated into the polymer matrix serves as a plasticizer.
Remark DOI: 10.1134/S0965545X11100014
Link

Autothermal Reforming of Methane in Proton-Conducting Ceramic Membrane Reactor

Authors Jay Kniep , Matthew Anderson , and Jerry Y.S. Lin
Source
Ind. Eng. Chem. Res.
Volume: 50, Issue: 22, Pages: 12426–12432
Time of Publication: 2011-10
Abstract Endothermic steam reforming of methane for hydrogen production requires heat input with selective oxidation of methane. Dense SrCe0.75Zr0.20Tm0.05O3-δ perovskite membranes were combined with a reforming catalyst to demonstrate the feasibility of a heat-exchange membrane reactor for steam reforming of methane coupled with selective oxidation of permeated hydrogen. The reforming catalyst used was a prereduced nickel based catalyst supported on γ-Al2O3. Hydrogen produced via the steam reforming of methane or water gas shift reaction was able to diffuse through the catalyst bed and transport through the membrane. The permeated hydrogen reacted with oxygen (from air) to produce heat for the steam reforming of methane on the other side of the membrane. The membrane reactor avoids the use of an expensive air separation unit to produce pure oxygen. The influence of experimental conditions, such as temperature, gas hourly space velocity, and the steam to carbon (S/C) ratio, on the membrane reactor was investigated. SrCe0.75Zr0.20Tm0.05O3-δ showed good chemical stability in steam reforming conditions as X-ray diffraction analysis of the membrane surface exposed to steam-reforming conditions for 425 h showed only minor CeO2 formation. The experimental data demonstrate the feasibility of using a proton conducting ceramic membrane in the heat-exchange membrane reactor for steam reforming of methane coupled with selective oxidation.
Remark Link

Post-heat treatment pressure effect on performances of metal-supported solid oxide fuel cells fabricated by atmospheric plasma spraying

Authors Chun-Huang Tsai, Chang-sing Hwang, Chun-Liang Chang, Jen-Feng Yu, Sheng-Hui Nien
Source
Journal of Power Sources
Volume: 197, Pages: 145–153
Time of Publication: 2012-01
Abstract The nickel metal-supported cells fabricated by atmospheric plasma spraying are post-heat treated in air at 960 C for 2 h with different pressures. The current–voltage–power and AC impedance measurements show the prepared cell with an applied pressure of 450 g cm−2 in the post-heat treatment has a better electrochemical performance at test temperatures ≥ 650 C. For test temperatures < 650 C, the maximum power densities at 450 g cm−2 pressure are about the same as the maximum power densities at 1250 g cm−2 pressure. The SEM micrograph indicates that the cathode including the cathode interlayer and the cathode collector is the most porous region in the cell. AC impedance results show this cathode is the most sensitive part to the applied pressure in the post-heat treatment and the cell with 450 g cm−2 pressure has the smallest low frequency intercept R2 and the polarization resistance Rp at temperatures from 600 to 800 C. The performance durability test of the cell post-heat treated at 450 g cm−2 pressure shows a degradation rate of 0.0087 mV h−1 or 0.0026 mW h−1 at 300 mA cm−2 constant current density and 750 C test temperature.
Keywords Atmospheric plasma spray; Solid oxide fuel cells; Metal-supported; Nanostructured
Remark Link

The morphotropic phase boundary in the (1 − x)PbZrO3–x[0.3Bi(Zn1/2Ti1/2)O3–0.7PbTiO3] perovskite solid solution

Authors T. Sareein, W. Hu, X. Tan and R. Yimnirun
Source
Journal of Materials Science
Volume: 47, Issue: 4, Pages: 1774-1779
Time of Publication: 2012-04
Abstract Ceramics in the (1 − x)PbZrO3–x[0.3Bi(Zn1/2Ti1/2)O3–0.7PbTiO3] solid solution system with 0.48 ≤ x ≤ 0.56 were investigated. A morphotropic phase boundary separating rhombohedral and tetragonal perovskite phases was identified at x = 0.52. This composition displays the maximum remanent polarization P r of 40.7 μC/cm2 and the best piezoelectric coefficient d 33 of 311 pC/N in the pseudo-binary system. However, the Curie temperature T c for this MPB composition is 291 C, much lower than initially expected.
Remark Link

Synthesis and electrical properties of lead free (Bi0.5K0.5)TiO3–BaTiO3–Bi(Zn0.5Ti0.5)O3 ceramics

Authors A. Prasatkhetragarn, B. Yotburut, N. Triamnak, R. Yimnirun and D.P. Cann
Source
Ceramics International
Volume: 38, Issue: 1, Pages: 827–830
Time of Publication: 2012-01
Abstract Lead free ferroelectric materials with high Curie temperature in (x)[(Bi0.5K0.5)TiO3]− (1-x)[0.5Bi(Zn0.5Ti0.5)O3 − 0.5BaTiO3] or (x)BKT − (1-x)[BZT − BT] ternary system, where x = 0.4, 0.5, 0.6 and 0.8, were synthesized. The single phase perovskite for all ceramics were formed at 900 C for 6 h in air. The ceramic compositions with x = 0.5 and 0.6 exhibited the dielectric properties with relaxor-like phase transition behavior, while the ceramic with x = 0.8 showed the dielectric behavior of normal ferroelectric materials. From room temperature P–E measurement, the maximum remnant polarization (Pr of 2.75 μC/cm2) and coercive field (Ec of 12.41 kV/cm) were obtained in the composition with x = 0.6. In addition, the TC, Pr and Ec were found trend to increase with increasing BKT content.
Keywords Ferroelectric; Dielectric; Relaxor-like behavior; High Curie temperature
Remark Link

Characterization of individual barium titanate nanorods and their assessment as building blocks of new circuit architectures

Authors K. Zagar, F. Hernandez-Ramirez, J. D. Prades, J. R. Morante, A. Rečnik and M. Čeh
Source
Nanotechnology
Volume: 22, Issue: 38, Pages: 385501
Time of Publication: 2011-09
Abstract In this work, we report on the integration of individual BaTiO3 nanorods into simple circuit architectures. Polycrystalline BaTiO3 nanorods were synthesized by electrophoretic deposition (EPD) of barium titanate sol into aluminium oxide (AAO) templates and subsequent annealing. Transmission electron microscopy (TEM) observations revealed the presence of slabs of hexagonal polymorphs intergrown within cubic grains, resulting from the local reducing atmosphere during the thermal treatment. Electrical measurements performed on individual BaTiO3 nanorods revealed resistivity values between 10 and 100 Ω cm, which is in good agreement with typical values reported in the past for oxygen-deficient barium titanate films. Consequently the presence of oxygen vacancies in their structure was indirectly validated. Some of these nanorods were tested as proof-of-concept humidity sensors. They showed reproducible responses towards different moisture concentrations, demonstrating that individual BaTiO3 nanorods may be integrated in complex circuit architectures with functional capacities.
Remark doi: 10.1088/0957-4484/22/38/385501
Link

Structure, chemical stability and mixed proton–electron conductivity in BaZr0.9−xPrxGd0.1O3−δ

Authors A. Magras, C. Frontera, A.E. Gunns, A. Tarancn, D. Marrero-Lpez, T. Norby and R. Haugsrud
Source
Journal of Power Sources
Time of Publication: 2011-08
Abstract BaZr0.9−xPrxGd0.1O3−δ (x = 0.3 and 0.6) was prepared by combustion synthesis and characterised with respect to conductivity and stability in an attempt to combine the desirable properties of the end members. The polycrystalline materials exhibit a cubic or pseudo-cubic structure as determined by X-ray synchrotron radiation and transmission electron microscopy. The chemical stability of the compositions is strongly dependent on the praseodymium content, the materials with more Pr present lower stability. Electron holes dominate the conductivity under oxidising atmospheres in BaZr0.3Pr0.6Gd0.1O3−δ, while BaZr0.6Pr0.3Gd0.1O3−δ exhibits a mixed electron hole–proton conducting behaviour. Substitution of Zr by Pr in acceptor-doped BaZrO3 decreases the sintering temperature and increases the grain growth rate.
Remark Article in press, DOI:10.1016/j.jpowsour.2011.06.076

Impedance and modulus spectroscopic studies on 40PrTiTaO6 + 60YTiNbO6 ceramic composite

Authors D. B. Dhwajam, M. Buchi Suresh, U. S. Hareesh, J. K. Thomas, S. Solomon, Annamma John
Source
Journal of Materials Science: Materials in Electronics
Volume: 23, Issue: 3, Pages: 653-658
Time of Publication: 2012-03
Abstract The 40PrTiTaO6 + 60YTiNbO6 ceramic composite is prepared through the solid state ceramic route. The structure is discussed using X-ray diffraction analysis. Surface morphology is examined by Scanning Electron Microscopy (SEM). Impedance and modulus spectroscopic studies are carried out. A decrease in the resistive behavior of the sample assisted by the grain boundary conduction with rise in temperature is found. The experimental results on electrical properties indicate that the material exhibits conduction both due to bulk and grain boundary effect. The microstructure was investigated by SEM micrographs in which grains separated by grain boundaries are visible. There is a probable change in the capacitance values of the material as a function of temperature. The relaxation time is small at higher temperatures than at lower temperatures. The activation energy is found as 1.52 eV, which suggests the possibility of electrical conduction due to the mobility of oxide ions (O2−) or oxide ion vacancies at higher temperature.
Remark Link

Proton Conductivity in Acceptor-Doped LaVO4

Authors Morten Huse, Truls Norby, and Reidar Haugsrud
Source
J. Electrochem. Soc.
Volume: 158, Issue: 8, Pages: B857-B865
Time of Publication: 2011-06
Abstract Electrical characterization of nominally undoped LaVO4, La0.99Ca0.01VO4− and La0.95Ca0.05VO4− was performed in various partial pressures of oxygen, water vapor and hydrogen isotopes, from 300 to 1100C by impedance spectroscopy, AC conductivity measurements (10 kHz) and EMF-measurements. XRD, SEM and EDS were used for structural, micro structural and compositional analysis. Acceptor doped LaVO4 is a pure ionic conductor in oxidizing atmospheres in the entire measured temperature range; dominated by proton conductivity at low temperatures (T < 450C) under wet conditions and oxide ion conductivity at high temperatures. A maximum in the partial proton conductivity of ~ 6 10−5 S/cm was reached at 900C (pH2O2.510-2 atm). Thermodynamics of hydration and transport parameters for charge carriers in La0.99Ca0.01VO4 were derived from relations between defect chemistry, transport properties and the measured conductivity data and revealed: S=− 130 10 J/mol K, S =− 142 10 J/mol K, H=− 110 10 kJ/mol, 0,H+ = 50 6 cm2 K/Vs, Hmob,H+ = 75 10 kJ/mol, 0,v= 120 20 cm2 K/Vs and Hmob,v = 85 10 kJ/mol. The tetrahedron (XO4) volume and migration enthalpy were found to be correlated for the series of monoclinic LaXO4.

Nanostructuring phenomena in oxygen-conducting complex oxides of heavy REE

Authors A. V. Shlyakhtina, D. A. Belov, S. Yu. Stefanovich and L. G. Shcherbakova
Source
Russian Journal of Electrochemistry
Volume: 47, Issue: 5, Pages: 620-627
Time of Publication: 2011-05
Abstract In complex oxides of REE (Ln4M3O12 (Ln = Tm, Lu; M = Zr, Hf), Ln2TiO5 (Ln = Er-Yb)) and Ho2TiO5, the following phase transitions of the order-disorder type are studied for different cooling rates: rhombohedral δ-phase-defective fluorite in Ln4M3O12 (Ln = Tm, Lu; M = Zr, Hf), pyrochlor-like phasedefective fluoride in Ln2TiO5 (Ln = Er-Yb), and hexagonal β-phase-pyrochlor in Ho2TiO5. The presence of nanostructuring phenomena typical of fluorite-like polymorphous modifications of complex oxides in the Ln2O3-MO2 (Ln = Ho-Lu; M = Ti, Zr, Hf) systems is confirmed. The conductivity of polymorphous modifications of Ln4Zr3O12 (Ln = Tm, Lu;) and Ln2TiO5 (Ln = Ho-Yb) with different thermal prehistory is studied. The comparative studies of the oxygen-ionic conductivity of fluorite- and pyrochlor-like Ln2TiO5 (Ln = Ho-Yb), pyrochlor Ho2TiO5, and β-Ho2TiO5 and also of the conductivity of fluorite-like compounds and δ-Ln4Zr3O12 (Ln = Tm, Lu) are carried out. The oxygen-ionic conductivity of complex oxides in the Ln2O3-MO2 (Ln = Er-Lu; M = Ti, Zr, Hf) system is shown to decrease in the following series: defective pyrochlor-defective fluorite-rhombohedral δ-phase ∼ hexagonal β-phase.

Partial Oxidation of Methane and Oxygen Permeation in SrCoFeOx Membrane Reactor with Different Catalysts

Author Jay Kniep and Y.S. Lin
Source
Ind. Eng. Chem. Res.
Volume: 50, Issue: 13, Pages: 7941–7948
Time of Publication: 2011-05
Abstract Partial oxidation of methane (CH4) and oxygen permeation in a dense SrCoFeOx disk membrane reactor were studied with the reducing side of the membrane packed with different catalysts (catalyst support γ-Al2O3, La0.6Sr0.4Co0.8Fe0.2O3−δ, and 10 wt % Ni/γ-Al2O3) of increasing reaction activities for CH4 oxidation. The influence of temperature, flow rates, and inlet CH4 concentration (diluted with helium) on the performance of the different membrane reactors was investigated. The oxygen permeation flux and CH4 conversion increased in the following order: γ-Al2O3 < La0.6Sr0.4Co0.8Fe0.2O3−δ < 10% Ni/γ-Al2O3. The membrane reactor with the reforming catalyst of 10 wt % Ni/γ-Al2O3 had the highest CH4 conversion (90%), CO selectivity (97%), and oxygen permeation flux (2.40 mL/(cm2 min)) at 900 C. The improvement of the oxygen permeation through the membranes with different catalysts emphasizes the effect of the CH4 oxidation reaction rate on the reducing side of the membrane on the oxygen permeation flux through the mixed-conducting ceramic membranes. Under identical conditions, the oxygen permeation flux through mixed-conducting ceramic membrane with a reducing gas is a strong function of the catalytic activity for the oxidation of the reducing gas.
Remark Link

Phase transition and electrical properties of gallium- and indium-doped Bi10Ti3W3O30

Authors E. P. Kharitonova, D. A. Belov, A. V. Mosunov and V. I. Voronkova
Source
Inorganic Materials
Volume: 47, Issue: 5, Pages: 513-520
Time of Publication: 2011-05
Abstract Polycrystalline samples of gallium- and indium-doped Bi10Ti3W3O30 (mixed-layer Aurivillius phase with the Ti4+ and W6+ distributed at random over the perovskite-like slabs) have been prepared by solid-state reactions, and their polymorphism and electrical properties have been studied. Doping with both In3+ and Ga3+ yields limited solid solutions and shifts the ferroelectric phase transition to lower temperatures. The heterovalent substitutions of In3+ and Ga3+ for Ti4+ and W6+ increase the oxygen vacancy concentration and, accordingly, the conductivity of the material relative to the undoped compound.

Lamellar Titanates: A Breakthrough in the Search for New Solid Oxide Fuel Cell Anode Materials Operating on Methane

Authors Cdric Prillat-Merceroz, Pascal Roussel, Rose-Nolle Vannier, Patrick Glin, Sbastien Rosini, Gilles Gauthier
Source
Advanced Energy Materials
Volume: 1, Issue: 4, Pages: 573–576
Time of Publication: 2011-07
Abstract Decreasing the dimensionality of the LaxSr1–xTiOmath image family structure from 3D to 2D by increasing the La content greatly enhances the electrochemical performance of the material as an SOFC anode. This is attested to by the strong decrease in the polarization resistance values deduced from the complex impedance spectra (Nyquist plot) recorded at 900 C in H2/H2O(3%) on a symmetrical cell.
Keywords Solid oxide fuel cells; Anode materials; Titanate; Methane
Remark Link

An ion-plasma technique for formation of anode-supported thin electrolyte films for IT-SOFC applications

Authors N.S. Sochugov, A.A. Soloviev, A.V. Shipilova, V.P. Rotshtein
Source
International Journal of Hydrogen Energy
Volume: 36, Issue: 9, Pages: 5550-5556
Time of Publication: 2011-05
Abstract This paper describes a preparation method and structural and electrochemical properties of a thin bilayer anode-electrolyte structure for a solid oxide fuel cell operating at intermediate temperatures (IT-SOFC). Thin anode-supported yttria-stabilized zirconia electrolyte films were prepared by reactive magnetron sputtering of a Zr–Y target in an Ar–O2 atmosphere. Porous anode surfaces of IT-SOFCs were modified by a pulsed low-energy high-current electron beam prior to film deposition; the influence of this pretreatment on the performance of both the deposited films and a single cell was investigated. The optimal conditions of the pulsed electron beam pretreatment were obtained. For the electrolyte thickness about 2.5 μm and the value of gas permeability of the anode/electrolyte structure 1.01 10−7 mol m−2 s−1 Pa−1, the maximum power density achieved for a single cell at 800 C and 650 C was found to be 620 and 220 mW cm−2 in air, respectively.
Keywords Solid oxide fuel cell; YSZ electrolyte; Magnetron sputtering; Surface modification of material; Pulsed electron beam treatment; Electrical performance

Microwave-assisted synthesis of gadolinia-doped ceria powders for solid oxide fuel cells

Authors A. Gondolini, E. Mercadelli, A. Sanson, S. Albonetti, L. Doubova and S. Boldrini
Source
Ceramics International
Volume: 37, Issue: 4, Pages: 1423-1426
Time of Publication: 2011-05
Abstract Gadolinia doped ceria (GDC) is an attractive electrolyte material for intermediate temperature solid oxide fuel cells (IT-SOFCs) for its high ionic conductivity at low temperature (500–700 C). A number of different methods are currently used to prepare nano-sized doped-ceria powder. Among the others, precipitation in solution remains the best method to obtain well-dispersed particles of controlled properties. In this work, nanocrystalline Ce1−xGdxO2−δ (GDC) particles were produced by polyol microwave assisted method in very mild conditions (170 C, 2 h, 1 atm). The as-synthesized powder showed good sinterability and ionic conductivity comparable to the ones of the corresponding nanometric commercial GDC.
Keywords GDC; Microwave heating; Polyol method; IT-SOFC

Solid oxide fuel cells with Sm0.2Ce0.8O2−δ electrolyte film deposited by novel aerosol deposition method

Authors Sea-Fue Wang, Yung-Fu Hsu, Chih-Hao Wang and Chin-Ting Yeh
Source
Journal of Power Sources
Volume: 196, Issue: 11, Pages: 5064-5069
Time of Publication: 2011-06
Abstract In this study, dense electrolyte ceramic Sm0.2Ce0.8O2−δ (SDC) thin films are successfully deposited on NiO-SDC anode substrate by aerosol deposition (AD) with oxygen as the carrier gas at the substrate temperature ranging from room temperature to 300 C. To remove the effect of humidity on the starting powders, this study found that, in depositing SDC films, having the starting powders preheat-treated at 200 C helped generate a smooth and dense layer, though a lower deposition rate was achieved. At a deposition time of 22 min, SDC films with a uniform thickness of 1.5 μm and grain sizes of ≈67 nm are obtained. SOFC single cells are then built by screen printing a LSCF cathode on the anode-supported substrates with SDC electrolyte. The cross-sectional SEM micrographs exhibit highly dense, granular, and crack-free microstructures. The open circuit voltages (OCV) of the single cells decrease with the rise in temperature, dropping from 0.81 V at 500 C to 0.59 V at 700 C. Maximum power densities (MPD) decline with decreasing operating temperature from 0.34 to 0.01 W cm−2 due to the increase of the R0 and RP of the single cells. The electrochemical results testify to the fine quality of SDC films as well as illustrate the electrolyte thickness effect and the effect of mixed ionic and electronic conduction of the SDC electrolyte in the reducing atmosphere.
Keywords SDC films, NiO-SDC substrate, aerosol deposition, Very dense SDC films, uniform thickness of 1.5 μm, Single cell with a MPD of 0.34 W cm−2, 700 C, Solid oxide fuel cell; Ceria; Aerosol deposition; Electrolyte

Conductivity, transport number measurements and hydration thermodynamics of BaCe0.2Zr0.7Y(0.1 − ξ)NiξO(3 − δ)

Authors S. Ricotea, The Corresponding Author, N. Bonanos, H.J. Wang and R. Haugsrud
Source
Solid State Ionics
Volume: 185, Issue: 1, Pages: 11-17
Time of Publication: 2011-03
Abstract BaCe0.2Zr0.7Y(0.1 − ξ)NiξO(3 − δ) compounds with ξ = 0.01 and 0.02 have been synthesized by solid state reaction at 1400 C and sintered at 1450 C. TEM analyses were performed and showed a segregation of nickel at the grain boundaries for ξ = 0.02. This apparent solubility limit of Ni in the B-site of the perovskite is in agreement with similar data obtained earlier for the two compositions. The first aim of this work was to evaluate the conductivity of BaCe0.2Zr0.7Y(0.1 − ξ)NiξO(3 − δ) at temperature between 500 and 900 C, using impedance spectroscopy at different oxygen partial pressures and water vapor pressures, as well as the emf technique. The compounds exhibit p-type conduction in oxidizing atmosphere, and ionic conduction elsewhere. The oxide ion contribution of the conductivity is negligible only for temperatures below 600 C. The determination of hydration enthalpies, our second goal, was achieved by modelling of the conductivity data and by thermogravimetric measurements (TG-DSC).

Fabrication and Characterization of Anode-Supported BaIn0.3Ti0.7O2.85 Thin Electrolyte for Solid Oxide Fuel Cell

Authors M. Rieu, P. K. Patro, T. Delahaye*, E. Bouyer
Source
International Journal of Applied Ceramic Technology
Article first published online: 28 MAR 2011
Time of Publication: 2011-03
Abstract BaIn0.3Ti0.7O2.85 (BIT07) is a promising electrolyte for solid oxide fuel cells, due to its chemical compatibility with most of the cathode electrode material such as LSM and Ln2NiO4. The present work is aimed on the fabrication of anode-supported half cells with thin BIT07 electrolyte. For this, Ni-8YSZ cermet was chosen due to its excellent mechanical and electrochemical properties, in addition to its low cost. The NiO–8YSZ anode support was prepared by tape casting, and for this, an organic slurry formulation was optimized. The BIT07 electrolyte thin film was deposited through screen printing on the green anode. The formulation of the ink was optimized, and sintering at 1350C for 3 h led to a dense electrolyte with controlled thickness varying from 2 to 12 μm. Further, the cermet electrode still had a homogeneous microstructure with well-defined anode/electrolyte interface. The electrode ASR was about 0.5 Ω cm2 and was stable over 500 h at 800C under H2–3% H2O. The fabrications of half cells were successfully scaled up to 100 mm 100 mm retaining the dimensional control and without any surface defects.

Curing of a network polyimide modified with a linear component

Authors D.A. Belov, S.Yu. Stefanovich, M.Yu. Yablokova
Source
Russian Journal of Applied Chemistry
Volume: 84, Issue: 2, Pages: 301-306
Time of Publication: 2011-03
Abstract The curing and relaxation processes in polymeric composites based on blends of network and linear polyimides applied onto a filler were studied by dielectric spectroscopy. The sensitivity of dielectric spectroscopy to processes occurring in the course of curing was examined.

Structure, Water Uptake, and Electrical Conductivity of TiP2O7

Authors Vajeeston Nalini, Magnus H. Srby, Koji Amezawa, Reidar Haugsrud, Helmer Fjellvg, Truls Norby
Source
Journal of the American Ceramic Society
Volume: 94, Issue: 5, Pages: 1514–1522
Time of Publication: 2011-05
Abstract We report here on the structure of TiP2O7 and electrical properties of nominally acceptor (Sc, Fe)-doped TiP2O7 synthesized by an aqueous phosphoric acid route. Structural characterization, including studies of the high-temperature phase transition in TiP2O7, was carried out by powder X-ray and neutron diffraction. Ceramic disks were sintered by the spark plasma technique and their conductivities were characterized as a function of p(O2) and p(H2O) in the temperature range of 500–1000C by means of AC constant frequency measurements and impedance spectroscopy. As reported earlier, the acceptor doping appears not to influence the defect structure of TiP2O7 significantly. Effects of H+/D+ isotope shift were utilized to identify proton conduction. The conductivity was independent of p(O2) at 500–900C under oxidizing conditions suggesting predominantly protonic conduction at these temperatures. Under reducing atmosphere n-type conductivity contributed to the total conductivity at the higher temperatures. p(H2O) dependencies of the conductivities are interpreted in terms of a defect-chemical model involving protons and oxygen interstitials as the dominating defects. The uptake of water was studied by thermogravimetry at high p(H2O) and the thermodynamics of the hydration reaction was derived. Finally, parameters for the mobility of protons were extracted by combining the conductivity and thermogravimetry data.
Remark Link

Microstructural characterization and electrical properties of spray pyrolyzed conventionally sintered or hot-pressed BaZrO3 and BaZr0.9Y0.1O3 − δ

Authors Paul Inge Dahl, Hilde Lea Lein, Yingda Yu, Julian Tolchard, Tor Grande, Mari-Ann Einarsrud, Christian Kjlseth, Truls Norby and Reidar Haugsrud
Source
Solid State Ionics
Volume: 182, Issue: 1, Pages: 32-40
Time of Publication: 2011-02
Abstract A spray pyrolysis route to BaZrO3 (BZ) and BaZr0.9Y0.1O2.95 (BZY) powders was developed starting from nitrate solutions. Homogeneous powders with a grain size of ~ 100 nm were achieved. A calcination of the powder was necessary to remove carbonates formed during the spray pyrolysis. Hot pressing was in comparison with conventional sintering more effective to enhance densification and suppress grain growth, and dense (> 96%) materials with homogeneous microstructure were obtained. The Y-substitution decreased the densification rate. Minor amounts of a secondary phase was observed at the grain boundary triple points of BZY, but the grain boundaries were otherwise found to be coherent and without significant secondary phase accumulation. Impedance spectroscopy vs T, pO2 and pH2O of conventionally sintered BZ and hot-pressed BZY demonstrated that the conductivity of BZ was orders of magnitude lower than compared to BZY. The conductivity of BZ displayed mixed proton and p-type electronic conduction characteristics in the grain interior which was depressed at the grain boundaries. The grain boundaries showed an additional n-type electronic conduction under reducing conditions. The conductivity characteristics were according to core-space charge layer theory. BZ seems to exhibit a larger ratio of p-type electronic to protonic conduction as compared to BZY, contrary to the prediction of simple defect chemistry.

BiFeO3–PbZrO3–PbTiO3 ternary system for high Curie temperature piezoceramics

Authors Wei Hu, Xiaoli Tan and Krishna Rajan
Source
Journal of the European Ceramic Society
Volume: 31, Issue: 5 Time of Publication: 2011-05
Abstract BiFeO3–PbZrO3–PbTiO3 ternary solid solution system was investigated for the development of piezoelectric ceramics with high Curie temperatures. The search for the morphotropic phase boundary (MPB) compositions in this ternary system started from mixing two MPB compositions: 0.70BiFeO3–0.30PbTiO3 and 0.52PbZrO3–0.48PbTiO3. The content of PbTiO3 was then further fine tuned in order to reach the appropriate volume fraction between the rhombohedral and tetragonal phases in the sintered ceramics. It was observed that the sintering temperature has a profound impact on the density, grain morphology, dielectric and ferroelectric properties of the ceramics. The composition that displays the best combined structure and properties was identified to be 0.648BiFeO3–0.053PbZrO3–0.299PbTiO3, with a Curie temperature TC of 560 C, a remanent polarization Pr of 15.0 μC/cm2, and a piezoelectric coefficient d33 of 64 pC/N.

Synthesis and characterization of Ca-substituted YAlO3 by pechini route for solid oxide fuel cells

Authors Ramya Hariharan, Prakash Gopalan
Source
Solid State Sciences
Volume: 13, Issue: 1, Pages: 168-174
Time of Publication: 2011-01
Abstract The high operating temperature requirement of solid oxide fuel cells demands electrolyte materials stable at temperatures around 800 C. The perovskite material YAlO3, with yttrium ion on the A-site and the aluminium ion on the B-site is being investigated as an electrolyte for solid oxide fuel cells. This work investigates the structure and electrical conductivity of undoped and Ca-doped YAlO3 compositions that has been synthesized by the Pechini route. The samples have been investigated by X-ray diffraction studies. The electrical conductivity studies have been performed using a.c impedance spectroscopy in the range 200–800 C in air. The doped YAlO3 of composition x = 0.1 exhibits a total conductivity of about 2.2 mS/cm at 800 C. The microstructural evaluation of the samples has been conducted by scanning electron microscopy coupled with energy dispersive spectrum analysis.

δ-Phase to defect fluorite (order–disorder) transition in the R2O3–MO2 (R = Sc; Tm; Lu; M = Zr; Hf) systems

Authors A.V. Shlyakhtina, D.A. Belov, S.Yu. Stefanovich, I.V. Kolbanev, O.K. Karyagina, A.V. Egorov, S.V. Savilov and L.G. Shcherbakova
Source
Materials Research Bulletin
Volume: 46, Issue: 4, Pages: 512–517
Time of Publication: 2011-04
Abstract We have studied the δ-phase to defectfluoriteF* (order–disorder) transition in the R4M3O12 (R = Sc, Tm, Lu; M = Zr, Hf) compounds. The temperature of the δ–F* phasetransition in Tm4Zr3O12 is ∼1600 C. The rate of this transition in R4Zr3O12 (R = Sc, Tm, Lu) decreases markedly with decreasing difference in ionic radius between the R3+ and Zr4+, leading to stabilization of the δ-phasesR4Zr3O12 with R = Sc and Lu at high temperatures (∼1600 C). During slow cooling (5 C/h), the high-temperature defectfluoritesF*-R2Hf2O7 (R = Tm, Lu) decompose reversibly to form the δ-phasesR4Hf3O12. Some of the materials studied exhibit microdomains formation effects, typical of the fluorite-related oxide compounds in the R2O3–MO2 (M = Ti, Zr, Hf) systems of the heavy rare earths. The high-temperature defectfluoritesF*-R4M3O12 (R = Tm, Lu; M = Zr, Hf) as a rule contain antiphase microdomains of δ-R4Zr3O12. After slow cooling (5 C/h), such microdomains are large enough for the δ-phase to be detected by X-ray diffraction. The conductivity data for R4M3O12 (R = Sc, Tm, Lu; M = Zr, Hf) and Ln2Hf2O7 (Ln = Dy, Lu) prepared by different procedures show that the rhombohedral phasesδ-R4M3O12 (R = Sc, Tm, Lu; M = Zr, Hf) are poorer conductors than the defectfluorites, with 740 C conductivity from 10−6 to 10−5 S/cm. The conductivity drops with decreasing rare-earth ionic radius and, judging from the Ea values obtained (1.04–1.37 eV), is dominated by oxygen ion transport. The highest conductivity, ∼6 10−4 S/cm at 740 C, is offered by the rapidly cooled F*-Dy2Hf2O7. In the fluorite homologous series, oxygen ion conductivity decreases in the orderdefect pyrochlore > defectfluorite > δ-phase.
Keywords Fluorite; δ-Phases R4M3O12; Pyrochlore; Order–disorder transition; Antiphase microdomains; High-temperature conductivity
Remark Link

Polymorphism and high-temperature conductivity of Ln2M2O7 (Ln = Sm─Lu; M = Ti, Zr, Hf) pyrochlores

Authors A.V. Shlyakhtina, L.G. Shcherbakova
Source
Solid State Ionics
Volume: 192, Issue: 1, Pages: 200–204
Time of Publication: 2011-06
Pyrochlore; Fluorite; Order─disorder; Defects; High-temperature conductivity; Ionic conductivity; Solid electrolyte

Proton conductivity in Sm2Sn2O7 pyrochlores

Authors K.E.J. Eurenius, E. Ahlberg and C.S. Knee
Source
Solid State Ionics
Volume: 181, Issue: 35-36, Pages: 1577-1585
Time of Publication: 2010-11
Abstract The electrical conductivity of the pyrochlore systems, Sm2Sn2O7, Sm1.92Ca0.08Sn2O7 − δ and Sm2Sn1.92Y0.08O7 − δ was studied using impedance spectroscopy under wet and dry gas (O2 and Ar) in the temperature range 150–1000 C. Enhancements of the bulk conductivity of all samples at temperatures up to ~ 550 C were observed for wet conditions consistent with significant levels of proton conduction. The presence of dissolved protons in the acceptor-doped materials, Sm1.92Ca0.08Sn2O7 − δ and Sm2Sn1.92Y0.08O7 − δ, is supported by infrared spectroscopy and thermogravimetric analysis. Proton conduction was confirmed by isotope effects under heavy water (O2/D2O and Ar/D2O). The A-site substituted sample Sm1.92Ca0.08Sn2O7 − δ yielded the highest levels of proton conduction and displayed mixed ionic and electronic conduction under dry oxidising conditions. Electron hole conduction dominates in dry oxygen for Sm2Sn1.92Y0.08O7 − δ and Sm2Sn2O7. For the A-site doped sample bulk and grain boundary conduction could be separated. The specific grain boundary conduction was calculated using the brick layer model and was found to be two orders of magnitude lower compared to the bulk conductivity. The unexpected increase in conductivity seen for the undoped sample under wet gas is discussed in the context of structural disorder and possible filling of the un-occupied anion site in the pyrochlore structure by OH-groups.
Keywords Sm2Sn2O7; Proton conductor; Pyrochlore; Oxide ion conductivity; p-type conductivity; Infra-red spectroscopy; Thermogravimetric analysis

Experimental and theoretical studies of hydrogen permeation for doped strontium cerates

Authors Maki Matsuka, Roger D. Braddock, Hiroshige Matsumoto, Takaaki Sakai, Igor E. Agranovski and Tatsumi Ishihara
Source
Solid State Ionics
Volume: 181, Issue: 29-30, Pages: 1328-1335
Time of Publication: 2010-09
Abstract Non-galvanic hydrogen permeation properties of SrCe0.95Yb0.05O3 − α (SCYb-5) and SrCe0.95Tm0.05O3 − α (SCTm-5) dense membranes were investigated in a ‘wet’ hydrogen atmosphere where water vapour partial pressures were well defined and monitored for the entire duration of the experiments. The theoretical modelling of hydrogen permeation flux for SCYb-5 and SCTm-5 was also undertaken, and compared with experimental results. The parameter tuning was also performed by fitting the model to the experimental data obtained in this study. The experimental hydrogen permeation flux for SCYb-5 and SCTm-5 dense membranes was 6.8e− 9 mol/cm2/s and 7.1e− 9 mol/cm2/s, respectively, under the upstream hydrogen partial pressure of 0.25 atm (25%H2/Ar) at 900 C. As expected, the hydrogen permeation flux increases with the increase in the upstream hydrogen partial pressures, reaching the maximum flux of 1.4e− 8 mol/cm2/s and 1.6e− 8 mol/cm2/s, for SCYb-5 and SCTm-5 respectively, under the upstream hydrogen partial pressure of 1 atm (100%H2) at 900 C. Previous modelling used hydrogen permeation data collected by others in a permeation test conducted in a ‘dry’ hydrogen atmosphere (with unknown water vapour pressures). The modelled hydrogen permeation flux agreed well with the experimental data attained in this study, for both SCYb-5 and SCTm-5 samples. The parameter tuning further improved the model predictions for those samples. It was apparent that the modelled hydrogen flux agreed better with the experimental data obtained in this study (i.e. in a wet hydrogen atmosphere with known water vapour pressures).
Keywords Dense ceramic membranes; Hydrogen permeation; Modelling

Directed integration of ZnO nanobridge sensors using photolithographically patterned carbonized photoresist

Authors Chien-Chih Huang, Brian D Pelatt and John F Conley Jr
Source
Nanotechnology
Volume: 21, Issue: 19 Time of Publication: 2010-05
Abstract A method for achieving large area integration of nanowires into electrically accessible device structures remains a major challenge. We have achieved directed growth and integration of ZnO nanobridge devices using photolithographically patterned carbonized photoresist and vapor transport. This carbonized photoresist method avoids the use of metal catalysts, seed layers, and pick and place processes. Growth and electrical connection take place simultaneously for many devices. Electrical measurements on carbonized photoresist/ZnO nanobridge/carbonized photoresist structures configured as three-terminal field effect devices indicate bottom gate modulation of the conductivity of the n-type ZnO channel. Nanobridge devices were found to perform well as ultraviolet and gas sensors, and were characterized as regards ultraviolet light pulsing, oxygen concentration, and humidity. The sensitivity of the three-terminal nanobridge sensors to UV light and oxygen was enhanced by application of a negative bottom gate voltage.

Yttria-stabilized zirconia thin film electrolyte produced by RF sputtering for solid oxide fuel cell applications

Authors Federico Smeacetto, Milena Salvo, Lakshmi Chandru Ajitdoss, Sergio Perero, Tomasz Moskalewicz, Stefano Boldrini, Lioudmila Doubova and Monica Ferraris
Source
Materials Letters
Volume: 64, Issue: 22, Pages: 2450-2453
Time of Publication: 2010-11
Abstract Thin film (40–600 nm) yttria-stabilized zirconia (YSZ) electrolytes for solid oxide fuel cells (SOFC) were deposited on NiO-YSZ anodes and fused silica substrates by RF sputtering, using low applied power without the use of post deposition annealing heat treatment. YSZ film showed a nanocrystalline structure and consisted of the Zr.85Y.15O1.93 (fcc) phase. The film was dense and the YSZ/anode interface was continuous and crack free. According to preliminary in-plane conductivity measurements (temperature range 550–750 C) on the YSZ film, the activation energy for ionic conduction was found to be 1.18 0.01 eV.
Keywords Thin films; Ceramics; Microstructure; Nanomaterials

High-temperature proton conductivity and defect structure of TiP2O7

Authors Vajeeston Nalini, Reidar Haugsrud and Truls Norby
Source
Solid State Ionics
Volume: 181, Issue: 11-12, Pages: 510-516
Time of Publication: 2010-04
Abstract Nominally undoped TiP2O7 and TiP2O7 with 2 mol-% substitution of Ti by Al were synthesized from TiO2 (Al2O3) and H3PO4(aq), sintered at 1050 C, and characterized by XRD, TEM and SEM. The electrical conductivity was investigated at 300–1000 C as a function of p(O2), p(H2O), and p(D2O). The material's phase transition around 700 C is clearly visible in the conductivity curves. Al substitution hardly increased the conductivity. The conductivity was higher in H2O- than in D2O-containing and dry atmospheres, indicating the dominance of proton conduction. The conductivity was accordingly mainly independent of p(O2). A slight increase in the conductivity with decreasing p(O2) at the highest temperatures was indicative of a minor contribution of n-type electronic conduction. The p(H2O) and temperature dependencies of the conductivity have been modelled as a sum of proton and electron partial conductivities under a situation with protons charge compensated by oxygen interstitials as dominating defects.
Keywords Titanium pyrophosphate; TiP2O7; Al-substituted TiP2O7; Proton conduction; Defect structure

Scandium stabilized zirconium thin films formation by e-beam technique

Authors Darius Virbukas, Giedrius Laukaitis, Julius Dudonis, Oresta Katkauskė and Darius Milčius
Source
Solid State Ionics
Volume: 184, Issue: 1, Pages: 10–13
Time of Publication: 2011-03
Abstract Scandiumstabilizedzirconium (10ScSZ) thin ceramic films were deposited by e-beam evaporation of (ZrO2)0.90(Sc2O3)0.10 micro powder (particle size 0.5 0.7 μm). The influence of deposition rate on formed thinfilms microstructure and electrical properties was studied. 10ScSZ thinfilms were deposited on two types of different substrates: optical quartz (SiO2) and Alloy-600 (Fe–Ni–Cr) substrates. Deposition rate was changed from 2 to 16 /s to test its influence on thinfilmformation and its properties. The microstructure of formed 10ScSZ thin ceramic films was studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Electrical parameters of formed thin ceramics were investigated in the frequency range from 0.1 Hz to 1.0 MHz (in temperature range from 473 to 873 K). The ionic conductivity of the deposited electrolyte 10ScSZ thinfilms was determined by impedance spectroscopy. It was determined that the deposition rate (in range from 2 to 16 /s) has influence on crystallite size. It increases by increasing the deposition rate from 18.4 to 26.9 nm. The XRD measurements show that the formed 10ScSZ thinfilms do not repeat the crystallographic phase of the initial evaporated powder material—it is changes from rhombohedra (initial powder) to cubic (the formed thinfilms).
Keywords Scandium stabilized zirconium (ScSZ); Ionic conductivity; Electron beam deposition; Solid oxide fuel cells (SOFC)
Remark Link

Effect of sintering temperature and sintering additives on ionic conductivity of LiSi2N3

Authors Eiichirou NARIMATSU, Yoshinobu YAMAMOTO, Toshiyuki NISHIMURA and Naoto HIROSAKI
Source
Journal of the Ceramic Society of Japan
Volume: 118 , Issue: 1381 , Pages: 837-841
Time of Publication: 2010-09
Abstract The effect of sintering temperature and sintering additives on the ionic conductivity of LiSi2N3 was studied by performing complex impedance measurements. LiSi2N3 materials were fabricated by the reaction of Li3N, Si3N4, and sintering additives at temperatures of 1873–2073 K. Dense hot-pressed bodies were obtained at 1973–2073 K in the case of undoped LiSi2N3 and at 1873 K in the case of Y2O3, CaF2, and B2O3 addition. The ionic conductivity increased greatly with increasing sintering temperature and exhibited a strong dependence on the type of sintering additive. When the sintering temperature was constant at 1873 K, although the conductivities of Y2O3-doped LiSi2N3 and CaF2-doped LiSi2N3 were lower than that of undoped LiSi2N3, the conductivity of B2O3-doped LiSi2N3 was higher than that of undoped LiSi2N3. The enhanced conductivity of B2O3-doped LiSi2N3 can be attributed to the increase in the density of the sintered material without the formation of a phase of significant resistance at the grain boundaries.
Remark Link

Defects and transport properties of Sr-doped LaP3O9

Authors Vajeeston Nalini, Reidar Haugsrud and Truls Norby
Source
Solid State Ionics
Volume: 181, Issue: 27-28, Pages: 1264-1269
Time of Publication: 2010-09
Abstract LaP3O9 and 2 mol-% Sr-doped LaP3O9 have been synthesized by the solid-state reaction method and the phase purity was characterized by powder X-ray diffraction and scanning electron microscopy. The AC conductivity of sintered disks was measured with two-point electrode setup in the temperature range 300 − 700 C under oxidizing and reducing conditions at different oxygen and water vapor (H2O or D2O) partial pressures by means of impedance spectroscopy. The water vapor dependency and isotope effect reveal that protons are the predominant charge carrier. The conductivity was mainly independent of the partial pressure of oxygen at all measured temperatures under both oxidizing and reducing conditions, suggesting only minor electronic conductivity. Hydration thermodynamics and transport parameters for the Sr-doped sample have been determined based on a defect chemical model applied to thermogravimetry and conductivity data.
Keywords Proton conductivity; LaP3O9; Sr-doped LaP3O9; Defect structure; Thermodynamic relations; Transport parameters

Charge carriers in grain boundaries of 0.5% Sr-doped LaNbO4

Authors Harald Fjeld, Despoina Maria Kepaptsogloub, Reidar Haugsrud and Truls Norby
Source
Solid State Ionics
Volume: 181, Issue: 3-4, Pages: 104-109
Time of Publication: 2010-02
Abstract The grain boundary and grain interior conductivities of La0.995Sr0.005NbO4 − δ have been studied by means of impedance spectroscopy at 400 C after quenching from different pH2O, pO2 and temperatures. Effects of H/D isotope shifts on the conductivity were, moreover, determined from 400 to 480 C under isothermal conditions. The microstructure and composition were characterized by scanning electron microscopy and transmission electron microscopy. On basis of the effects of pH2O and H/D isotope exchange on the grain boundary and grain interior conductivities, it is concluded that protons are the major charge carrier and, furthermore, that they are relatively more predominating in the grain boundaries than in the grain interior. Ionic transport in the grain boundaries is discussed in terms of the grain boundary core–space charge layer model.
Keywords LaNbO4; Grain boundaries; Impedance spectroscopy; TEM; Space charge effects

Electrical Properties and Gas Sensing Characteristics of the Al2O3/4H SiC Interface Studied by Impedance Spectroscopy

Authors Pawel A. Sobas, Ola Nilsen, Helmer Fjellvg, Bengt G. Svensson
Source
Materials Science Forum
Silicon Carbide and Related Materials 2009
Volume: 645 - 648, Pages: 531-534
Time of Publication: 2010-04
Abstract Using impedance spectroscopy (IS) for characterization of the electrical properties and gas sensing characteristics of Al2O3/4H-SiC (MOS) structures, insight on the capacitive and resistive contributions in the interfacial region of the MOS structures is obtained. Applying DC bias voltages between accumulation and depletion (corresponding to the interfacial region) allows investigation of the voltage shift of the capacitance versus voltage (CV) curve at different temperatures and atmospheres. This voltage shift forms the basis to use the MOS structure as a gas sensor. The MOS capacitance, as extracted from IS data, is different from the one obtained using CV measurements, due to the ability of distinguishing the resistive contribution (using IS). Voltage shifts between 1 and 2 V are clearly revealed during exposure to hydrogen and oxygen, and this shift exhibits a long-term stability of operation at temperatures up to 500C. Hence, Al2O3 exhibits great promise as a gate dielectric in MOS-based gas detecting devices for use at elevated temperatures.
Keywords Impedance Spectroscopy, MOS Capacitor

Improved Proton Conductivity in Spark-Plasma Sintered Dense Ceramic BaZr0.5In0.5O3−delta

Authors Istaq Ahmed, Francis G. Kinyanjui, Patrick Steegstra, Zhijian J. Shen, Sten-G. Eriksson, and Mats Nygren
Source
Electrochem. Solid-State Lett.
Volume: 13, Issue: 11, Pages: B130-B134
Time of Publication: 2010-11
Abstract Spark-plasma sintering method was used to prepare dense proton conducting perovskite oxide BaZr0.5In0.5O3−delta. Analysis of X-ray powder diffraction data showed that the sample adopt the cubic crystal structure having the space group Pm[overline 3]m. Thermogravimetric analysis of prehydrated samples showed significant mass losses beyond 300C due to loss of protons as water vapor. Scanning electron microscope images show that the grain size of the spark-plasma sintered dense sample was smaller than that of solid-state sintered porous sample. The highest total proton conductivity (210−3 S cm−1 at 450C) was found for dense spark-plasma sintered sample under wet H2 than the samples prepared by other routes.

Oxygen bulk diffusion and surface exchange in Sr-substituted La2NiO4 + δ

Authors Zuoan Li, Reidar Haugsrud and Truls Norby
Source
Solid State Ionics
Volume: 184, Issue: 1, Pages: 42–46
Time of Publication: 2011-03
Abstract The oxygen bulk diffusion and surface exchange in Sr-substituted La2NiO4 + δ were investigated separately in this work. The oxygen flux through La2−xSrxNiO4 + δ (x = 0.1 and 0.2) was measured as a function of temperature and the oxygen self diffusion coefficients, DO, were extracted. The results show that the higher the Sr concentration, the lower the oxygen permeation and the higher the activation energy of DO. The surface exchange rate was determined by measuring isotope exchange with a mass spectrometer. The Sr substitution leads to higher surface exchange rate with lower activation energy. The incorporation of ionized atomic oxygen into surface vacancies was suggested to be the rate determining step.
Keywords Oxygen diffusion; Defect chemistry; Surface exchange; Rate determining step (rds); La2NiO4 + δ; La2−xSrxNiO4 + δ
Remark Link

Development of an In Situ Surface Deformation and Temperature Measurement Technique for a Solid Oxide Fuel Cell Button Cell

Authors Huang Guo, Gulfam Iqbal, Bruce S. Kang
Source
International Journal of Applied Ceramic Technology
Volume: 7, Issue: 1, January/February, Pages: 55-62
Time of Publication: 2010-01
Abstract A novel experimental technique is developed to measure the in situ surface deformation and temperature of a solid oxide fuel cell (SOFC) anode surface along with the cell electrochemical performance. The experimental setup consists of a NexTech ProboStat™ SOFC button cell test apparatus integrated with a Sagnac interferometric optical method and an infrared sensor for in situ surface deformation and temperature measurements, respectively. The button cell is fed with hydrogen or simulated coal syngas under SOFC operating conditions. The surface deformation is measured over time to estimate the anode structural degradation. The cell surface transient temperature is also monitored with different applied current densities under hydrogen and simulated coal syngas. The experimental results are useful to validate and develop SOFC structural durability and electrochemical models.

Synthesis; Functionalization; and Environmental Stabilization of ZnO Nanobridge Transducers for Gas and Liquid-phase Sensing

Authors A.D. Mason, C.-C. Huang, S. Kondo, M.T. Koesdjojo, Y.H. Tennico, V.T. Remcho and J.F. Conley Jr.
Source
Sensors and Actuators B: Chemical
Volume: 155, Issue: 1, Pages: 245–252
Time of Publication: 2011-07
Abstract Three methods of functionalizing ZnO NW surfaces with biotin were demonstrated. Biotinylated ZnO NWs were found to dissolve during exposure to deionized (DI) water, so a chemical vapor deposition (CVD) process was developed for parylene-A, a common moisture barrier with an amine group which allows further functionalization. Parylene-A coated ZnO NWs were found to be resistant to dissolution. Electrical measurements on parylene-A coated nanobridge devices showed normal operation with higher dark current and an attenuated response to UV and O2, indicating the ability to modulate environmental sensitivity. This work demonstrates the novel use of parylene-A coatings as an encapsulation layer as well as a potential starting platform for general functionalization of ZnO NW devices for selective sensing.
Keywords ZnO; Nanowires; Functionalization; Sensors
Remark Link

Correlation between microstructure and electrical conductivity in composite electrolytes containing Gd-doped ceria and Gd-doped barium cerate

Authors Mudrika Khandelwal, A. Venkatasubramanian, T.R.S. Prasanna and P. Gopalan
Source
Journal of the European Ceramic Society
Volume: 31, Issue: 4, Pages: 559–568
Time of Publication: 2011-04
Composite; Ceria; Impedance spectroscopy; Electrical conductivity; Fuel cell
Remark Link

The properties of scandium and cerium stabilized zirconium thin films formed by e-beam technique

Authors Darius Virbukas, Giedrius Laukaitis, Julius Dudonis and Darius Milčius
Source
Solid State Ionics
Volume: 188, Issue: 1, Pages: 46–49
Time of Publication: 2011-04
Abstract Scandium and ceriumstabilizedzirconium (10Sc1CeSZ) thin ceramic films were formed evaporating (ZrO2)0.89(CeO2)0.01(Sc2O3)0.10 micro powder using e-beam evaporation technique. The influence of deposition rate on formedthinfilms electrical properties and microstructure was studied. 10Sc1CeSZ thinfilms were deposited on two types of different substrates: optical quartz (SiO2) and Alloy 600 (Fe–Ni–Cr). Deposition rate was changed from 2 to 16 /s to understand its influence on thinfilm formation and other properties. The formed 10Sc1CeSZ thinfilms keep the cubic crystal structure as the initial evaporated powder material but change the main crystallographic peak from (111) to (200) for both types of substrate and used deposition rates. It was determined that the crystallites size increases from 19.0 to 24.9 nm and from 15.6 to 19.9 nm on optical quartz and Alloy 600 respectively by increasing the deposition rate (in range from 2 to 16 /s). The thinfilm density decreases by increasing the deposition rate. The ionic conductivity of 10Sc1CeSZ thinfilms was determined by impedance spectroscopy in the frequency range from 0.1 Hz to 1.0 MHz in temperature range from 473 K to 873 K. The best ionic conductivity σtot = 4.91 10− 2 Sm− 1 at 873 K temperature and the lowest value of activation energy ΔEa = 0.88 eV were found for 10Sc1CeSZ thinfilmsformed at 4 /s deposition rate.
Keywords Scandium and cerium stabilized zirconium (10Sc1CeSZ); Electron beam deposition; Solid oxide fuel cells (SOFC); Ionic conductivity
Remark Link

Ethanol internal steam reforming in intermediate temperature solid oxide fuel cell

Authors Stefan Diethelm, Jan Van Herle
Source
Journal of Power Sources
Volume: 196, Issue: 17, Pages: 7355–7362
Time of Publication: 2011-09
Abstract This study investigates the performance of a standard Ni–YSZ anode supported cell under ethanolsteamreforming operating conditions. Therefore, the fuelcell was directly operated with a steam/ethanol mixture (3 to 1 molar). Other gas mixtures were also used for comparison to check the conversion of ethanol and of reformate gases (H2, CO) in the fuelcell. The electrochemical properties of the fuelcell fed with four different fuel compositions were characterized between 710 and 860 C by I–V and EIS measurements at OCV and under polarization. In order to elucidate the limiting processes, impedance spectra obtained with different gas compositions were compared using the derivative of the real part of the impedance with respect of the natural logarithm of the frequency. Results show that internalsteamreforming of ethanol takes place significantly on Ni–YSZ anode only above 760 C. Comparisons of results obtained with reformate gas showed that the electrochemical cell performance is dominated by the conversion of hydrogen. The conversion of CO also occurs either directly or indirectly through the water–gas shift reaction but has a significant impact on the electrochemical performance only above 760 C.
Keywords SOFC; Ni–YSZ anode; Ethanol; Internal reforming; Coking; Impedance spectroscopy
Remark Link

Synthesis and electrical properties of Gd2MO5 (M = Zr, Hf)

Authors L. P. Lyashenko, L. G. Shcherbakova, D. A. Belov, E. I. Knerel’man and N. N. Dremova
Source
Neorganicheskie Materialy
Volume: Vol. 46, No. 12, Pages: pp. 1476–1482
Time of Publication: 2010-08
Abstract Polycrystalline Gd2ZrO and Gd2HfO5 have been prepared by heat-treating coprecipitated oxide mixtures, and their order-disorder phase transitions have been studied in the range 20–1600C. The materials have been shown to consist of nanostructured grains with a nanodomain size of ∼40 nm. Their electrical conductivity has been determined by impedance spectroscopy in air between 300 and 1000C. The 1000C conductivities of Gd2ZrO5 and Gd2HfO5 are 3.7 10−3 and 1.8 10−3 S/cm, and the respective effective activation energies are 1.37 and 1.56 eV.

Proton Conductivity in Mixed B-Site Doped Perovskite Oxide BaZr0.5In0.25Yb0.25O3−delta

Authors Istaq Ahmed,1,2 Francis G. Kinyanjui,1 Seikh M. H. Rahman,1 Patrick Steegstra,3 Sten G. Eriksson,1 and Elisabet Ahlberg3
Source
J. Electrochem. Soc.
Volume: Volume 157, Issue: Issue 12, Pages: B1819-B182
Time of Publication: 2010-12
Abstract A wet chemical route was used to prepare the oxygen deficient codoped perovskite oxide BaZr0.5In0.25Yb0.25O3−. Analysis of X-ray powder diffraction data showed that the sample belongs to the cubic crystal system with space group Pmm. Dynamic thermogravimetric (TG) analysis confirmed complete filling of oxygen vacancies (V) by protonic defects (OH) during the hydration process. The proton conductivity was investigated by impedance spectroscopy. The bulk and total conductivities of prehydrated BaZr0.5In0.25Yb0.25O3− were found to be 8.510−4 and 2.210−5 S cm−1, respectively, at 300C. The total conductivity in the codoped perovskite oxide was higher compared to that of the respective single doped perovskite oxides with the same doping level. The bulk and grain-boundary mobility and diffusion coefficients of protons were calculated at 200C using impedance and TG data to obtain the conductivity and proton concentration, respectively. The high bulk diffusivity (2.310−7 cm2 s−1) was obtained which indicates that the protons are more free to move in the heavily doped matrix compared to the lightly doped systems where trapping of protons occurs.
Keywords barium compounds, proton exchange membrane fuel cells, thermal analysis, vacancies (crystal), X-ray diffraction, zirconium compounds
Remark Link

Electrical Conductivity of Nanostructured Fluorite-Like Sc2Ti3O12

Authors L.P. Lyashenko, L.G. Shcherbakova, D.A. Belov, and A.V. Knotko
Source
Inorganic Materials
Volume: 45, Issue: 5, Pages: 543-549
Time of Publication: 2009
Abstract Single-crystal and polycrystalline samples of Sc4Ti3O12 have been shown to contain nanodomains (10–50 nm) with different degrees of ordering, coherent with the fluorite-like matrix. The oxygen-ion conductivity of this compound has been determined in the range 300–1000C in air using impedance spectroscopy. The nanostructured single-crystal and polycrystalline samples are close in the activation energy for bulk conduction at both low and high temperatures: ≃1.26 and 1.29 eV in the range 300–775C, ≃1.98 and 2.07 eV in the range 775–1000C.

Hydrogen sensitivity of doped CuO/ZnO heterocontact sensors

Author Seymen Aygn and David Cann
Source
Sensors and Actuators B: Chemical
Volume: 106, Issue: 2, Pages: 837-842
Time of Publication: 2005
Abstract Heterocontact sensors based on p-type CuO and n-type ZnO ceramics have been shown to exhibit a high sensitivity to reducing gas species and an intrinsic selectivity. In this work, doped heterocontact sensors were prepared via solid state synthesis routes. CuO was doped with various monovalent (Li, Na) and isovalent (Ca, Sr, Ni) dopants at different compositions to form both single phase and two phase samples. Effects of dopants on hydrogen sensitivity through conductivity and heterogeneous microstructure were investigated using dc current–voltage measurements and ac impedance analysis. It was observed that both monovalent and divalent dopants increased the hydrogen sensitivity significantly. The highest sensitivity was observed in a 2.5 mol% Ni-CuO/ZnO heterocontact and low amounts of Li doping were shown to greatly enhance the rectifying characteristics.
Keywords Hydrogen sensor; Heterocontact; CuO; ZnO

Synthesis, densification and electrical properties of strontium cerate ceramics

Authors Paul Inge Dahl, 1, Reidar Haugsrud, Hilde Lea Lein, Tor Grande, Truls Norby and Mari-Ann Einarsrud
Source
Journal of the European Ceramic Society
Volume: 27, Issue: 16, Pages: 4461-4471
Time of Publication: 2007

Stability and conductivity study of the BaCe0.9−xZrxY0.1O2.95 systems

Author Zhimin Zhong
Source
Solid State Ionics
Volume: 178, Issue: 3-4, Pages: 213-220
Time of Publication: 2007

Defects and transport properties in Ln6WO12 (Ln = La, Nd, Gd, Er)

Author Reidar Haugsrud
Source
Solid State Ionics
Volume: 178, Issue: 7-10, Pages: 555-560
Time of Publication: 2007

Phase transitions and ferroelectric properties in BiScO3-Bi(Zn1/2Ti1/2)O3-BaTiO3 solid solutions

Authors Chien-Chih Huang, David P. Cann, Xiaoli Tan, and Naratip Vittayakorn
Source
Journal of Applied Physics
Volume: 102, Issue: 4, Pages: 044103
Time of Publication: 2007

Shrinkage Effects of the Conduction Zone in the Electrical Properties of Metal Oxide Nanocrystals: The Basis for Room Temperature Conductometric Gas Sensor

Authors M. Manzanares, T. Andreu, J. D. Prades, J. Arbiol, F. Hernandez-Ramrez, A. Cirera and J. R. Morante
Source
Journal of Sensors
Volume: 2009, Pages: 1-7, doi:10.1155/2009/783675
Time of Publication: 2009

Preparation, electrical and thermal properties of new exfoliated graphite-based composites

Authors I.М. Afanasov, V.А. Morozov, A.V. Kepman, S.G. Ionov, A.N. Seleznev, G. Van Tendeloo and V.V. Avdeev
Source
Carbon
Volume: 47, Issue: 1, Pages: 263-270
Time of Publication: 2009

Structure, defect chemistry, and proton conductivity in nominally Sr-doped Ba3La(PO4)3

Authors N. Sharova, H. Fjellvg, T. Norby
Source
Solid State Ionics
Volume: 180, Issue: 4-5, Pages: 338-342
Time of Publication: 2009

Local structure and ionic conductivity in the Zr2Y2O7–Y3NbO7 system

Authors Stefan T Norberg, Istaq Ahmed, Stephen Hull, Dario Marrocchelli and Paul A Madden
Source
Journal of Physics: Condensed Matter
Volume: 21, Issue: 21, Pages: 215401
Time of Publication: 2009

Thin film chemical sensors based on p-CuO/n-ZnO heterocontacts

Authors C.S. Dandeneau, Y.H. Jeon, C.T. Shelton, T.K. Plant, D.P. Cann and B.J. Gibbons
Source
Thin Solid Films
Volume: 517, Issue: 15, Pages: 4448-4454
Time of Publication: 2009

Phase formation, microstructure, and dielectric properties of (1 − x)PZT–(x)PCN ceramics

Authors A. Prasatkhetragarn, P. Ketsuwan, S. Ananta, R. Yimnirun and D.P. Cann
Source
Materials Letters
Volume: 63, Issue: 15, Pages: 1281-1284
Time of Publication: 2009

Characterization of porous lanthanum strontium manganite (LSM) and development of yttria stabilized zirconia (YSZ) coating

Authors A.K. Sahu, A. Ghosh and A.K. Suri
Source
Ceramics International
Volume: 35, Issue: 6, Pages: 2493-2497
Time of Publication: 2009

Ordering processes in Ln2TiO5 (Ln = Dy–Lu): The role of thermal history

Authors A.V. Shlyakhtina, D.A. Belov, O.K. Karyagina and L.G. Shcherbakova
Source
Journal of Alloys and Compounds
Volume: 479, Issue: 1-2, Pages: 6-10
Time of Publication: 2009

Effects of Zr/Ti ratio on dielectric and ferroelectric properties of 0.8Pb(ZrxTi1−x)O3–0.2Pb(Co1/3Nb2/3)O3 ceramics

Authors A. Prasatkhetragarna, M. Unruan, A. Ngamjarurojana, Y. Laosiritaworn, S. Ananta, R. Yimnirun and D. P. Cann
Source
Current Applied Physics
Volume: 9, Issue: 4, Pages: 802-806
Time of Publication: 2009

Ce0.9Sr0.1VOx (x = 3, 4) as anode materials for H2S-containing CH4 fueled solid oxide fuel cells

Authors Nemanja Danilovic, Jing-Li Luo, Karl T. Chuang and Alan R. Sanger
Source
Journal of Power Sources
Volume: 192, Issue: 2, Pages: 247-257
Time of Publication: 2009

Acceptor doping of Ln2Ti2O7 (Ln = Dy, Ho, Yb) pyrochlores with divalent cations (Mg, Ca, Sr, Zn)

Authors D.A. Belov, A.V. Shlyakhtina, S.Yu. Stefanovich, I.V. Kolbanev, Yu.A. Belousov, O.K. Karyagina and L.G. Shcherbakova
Source
Materials Research Bulletin
Volume: 44, Issue: 8, Pages: 1613-1620
Time of Publication: 2009

Effect of substitution with Cr3+ and addition of Ni on the physical and electrochemical properties of Ce0.9Sr0.1VO3 as a H2S-active anode for solid oxide fuel cells

Authors N. Danilovic, J.L. Luo, K. T. Chuang and A. R. Sanger
Source
Journal of Power Sources
Volume: 194, Issue: 1, Pages: 252-262
Time of Publication: 2009

Dielectric and ferroelectric properties of 0.8PZT–0.2PCN ceramics under sintering conditions variation

Authors A. Prasatkhetragarna, M. Unruan, A. Ngamjarurojana, Y. Laosiritaworn, S. Ananta, R. Yimnirun and D. P. Cann
Source
Current Applied Physics
Volume: 9, Issue: 5, Pages: 1165-1169
Time of Publication: 2009

Conductivity and water uptake of Sr4(Sr2Nb2)O11nH2O and Sr4(Sr2Ta2)O11nH2O

Authors Niina Jalarvo, Camilla Haavik, Camilla Kongshaug, Poul Norby and Truls Norby
Source
Solid State Ionics
Volume: 180, Issue: 20-22, Pages: 1151-1156
Time of Publication: 2009

Synthesis and characterization of nanocrystalline Ni–YSZ cermet anode for SOFC

Author T. Priyatham and Ranjit Bauri
Source
Materials Characterization
Volume: 61, Issue: 1, Pages: 54-58
Time of Publication: 2010-01
Abstract Ni–YSZ cermet anode has been synthesized in one step using a simple and cost effective combustion synthesis process. The processed powder of NiO–YSZ is found to be nanocrystalline with crystallite sizes of 29 and 22 nm for NiO and YSZ respectively by X-ray diffraction and transmission electron microscopy analysis. X-ray diffraction analysis also shows that the precursor salts are converted to highly crystalline phases of NiO and YSZ (8 mol% Y2O3) without any intermediate calcination step and no undesirable phases are present. Comparison with the X-ray diffraction pattern of a commercial YSZ sample shows that the process is also effective in maintaining a close compositional control. The microstructure of the sintered and reduced sample shows a well defined network of pores which is necessary for the effective functioning of the anode. The electrical conductivity as a function of temperature shows metallic behavior.
Keywords Ni–YSZ anode; Combustion synthesis; Nanocrystalline cermet; Microstructure

A combined conductivity and DFT study of protons in PbZrO3 and alkaline earth zirconate perovskites

Authors Tor S. Bjrheim, Akihide Kuwabara, Istaq Ahmed, Reidar Haugsrud, Svein Stlen and Truls Norby
Source
Solid State Ionics
Volume: 181, Issue: 3-4, Pages: 130-137
Time of Publication: 2010
Abstract The electrical properties of nominally undoped and 4 mol% Y-doped PbZrO3 have been investigated by AC conductivity measurements and impedance spectroscopy under various pH2O and pO2 at high temperatures. The results indicate that the defect structures are dominated by acceptors (Y dopant and/or Pb vacancies formed during synthesis). In dry atmosphere and at high temperatures, the acceptors are compensated by oxygen vacancies. These are hydrated and replaced by protonic defects (hydroxide ions on oxide ion sites) at higher pH2O and lower temperatures. In oxidizing atmospheres, a minority concentration of electron holes dominates the conductivity. At lower temperatures and in wet atmosphere, a significant protonic conductivity contribution is also observed. Based on pO2 and pH2O isotherms, a model for incorporation of protonic defects has been applied, and the standard enthalpy of hydration of oxygen vacancies in undoped PbZrO3 has been determined (− 1.07 0.13 eV). The measured total conductivities are influenced by high grain boundary resistance. Hence, the enthalpy is at the present stage assigned to the polycrystalline ceramic material as such. Rough estimates of bulk proton mobility in Y-doped PbZrO3 yield uH+0 = 17 cm2K/Vs and ΔHm,H+ = 0.93 eV. A complementary DFT study of the hydration thermodynamics of PbZrO3 and the alkaline earth zirconate perovskites AZrO3 (A = Ca, Sr, Ba) is also reported. The experimental and theoretical hydration enthalpies are compared with those of other ABO3 perovskites. Correlations between the hydration thermodynamics and other properties of the materials are discussed.
Keywords PbZrO3; CaZrO3; SrZrO3; BaZrO3; Conductivity; Proton; Proton mobility; DFT; Thermodynamics; Defects; Hydration

Electrical conductivity and oxygen permeation properties of SrCoFeOx membranes

Authors Jay Kniep, Qinghua Yin, Izumi Kumakiri and Y.S. Lin
Source
Solid State Ionics
Volume: 180, Issue: 40, Pages: 1633-1639
Time of Publication: 2010
Abstract The total conductivity and oxygen permeation properties of dense SrCoFeOx membranes synthesized from the solid state method were studied in the temperature range of 700–900 C. The SrCoFeOx membranes consist of an intergrowth (Sr4Fe6 − xCoxO13 δ), perovskite (SrFe1 − xCoxO3 − δ), and spinel (Co3 − xFexO4) phase. SrCoFeOx exhibits n-type and p-type conduction at low and high oxygen partial pressures, respectively, and has a total conductivity of 16.5 S/cm at 900 C in air. The oxygen permeation fluxes for SrCoFeOx and SrFeCo0.5Ox membranes were measured with either an inert or carbon monoxide sweep gas. The oxygen permeation fluxes were higher through SrCoFeOx membranes than SrFeCo0.5Ox membranes and can be attributed to a difference in the amount and makeup of the perovskite phase present in each composition. The oxygen permeation fluxes with a carbon monoxide sweep gas were approximately two orders of magnitude larger than the fluxes measured with an inert sweep gas for both compositions. The large oxygen permeation fluxes observed with a carbon monoxide sweep are due to a higher driving force for oxygen transport and a reaction on the sweep side of the membrane that maintains a low oxygen partial pressure.
Keywords Mixed-conducting oxide membrane; Oxygen permeation; Strontium iron cobalt oxide

Transport properties and defect analysis of La1.9Sr0.1NiO4 + δ

Authors Zuoan Li, Reidar Haugsrud, Jens B. Smith and Truls Norby
Source
Solid State Ionics
Volume: 180, Issue: 26-27, Pages: 1433-1441
Time of Publication: 2009

Investigation of proton conductivity in Sm1.92Ca0.08Ti2O7 − δ and Sm2Ti1.92Y0.08O7 − δ pyrochlores

Authors K.E.J. Eurenius, E. Ahlberg, I. Ahmed, S.G. Eriksson and C.S. Knee
Source
Solid State Ionics
Volume: 181, Issue: 3-4, Pages: 148-153
Time of Publication: 2010
Abstract The results of the synthesis and characterisation of pyrochlore systems Sm1.92Ca0.08Ti2O7 − δ and Sm2Ti1.92Y0.08O7 − δ are reported. The electrical conductivity of the materials was studied using impedance spectroscopy under wet and dry oxygen and argon. Enhancements of the bulk conductivity at temperatures up to 500 C were observed for wet conditions indicative of significant proton conductivity. The presence of dissolved protons in the materials is supported by thermogravimetric analysis and infrared spectroscopy. Proton conduction was confirmed by measurements in O2/D2O and Ar/D2O. The results reveal the importance of the correct choice of dopant site for the pyrochlore structure, with A-site substitution yielding the highest levels of proton, as well as oxide ion, conduction. For both samples bulk, rather than grain boundary, conduction is found to be dominant.
Keywords Sm2Ti2O7; Pyrochlore; Ionic conductivity; Infrared spectroscopy; Impedance spectroscopy

Space–charge theory applied to the grain boundary impedance of proton conducting BaZr0.9Y0.1O3 − δ

Authors C. Kjolseth, , H. Fjeld, O. Prytz, P.I. Dahl, C. Estournes, R. Haugsrud, T. Norby
Source
Solid State Ionics
Volume: 181, Issue: 5-7, Pages: 268-275
Time of Publication: 2010
Abstract The specific grain interior and grain boundary conductivities, obtained from impedance spectroscopy and the brick layer model, are reported for BaZr0.9Y0.1O3 − δ as a function of pO2 and temperature. pO2-dependencies were indicative of dominating ionic and p-type electronic conduction for the grain interior under reducing and oxidizing conditions, respectively, while the grain boundaries showed an additional n-type electronic contribution under reducing conditions. Transmission electron microscopy revealed enrichment of Y in the grain boundary region. These findings indicate the existence of space–charge layers in the grain boundaries. A grain boundary core–space–charge layer model is therefore applied to interpret the data. Using a Mott–Schottky approximation, a Schottky barrier height of 0.5–0.6 V and an effective grain boundary width of 8–10 nm (= 2 space–charge layer thickness) is obtained at 250 C in wet oxygen. Finite-element modelling of the complex impedance over a grain boundary with a space–charge layer depletion of protons yields a distorted semicircle as observed in the impedance spectra.
Keywords BaZrO3; BaZr0.9Y0.1O3 − δ; Proton conductivity; Grain boundary resistance; Impedance spectroscopy; Space–charge layer

Ceria and copper/ceria functional coatings for electrochemical applications: Materials preparation and characterization

Authors J. Melnik, X.Z. Fu, J.L. Luo, A.R. Sanger, K.T. Chuang, Q.M. Yang
Source
Journal of Power Sources
Volume: 195, Issue: 8, Pages: 2189-2195
Time of Publication: 2010
Abstract Following preliminary investigations, two electrodeposition techniques (electrophoretic and electrolytic) were selected and adapted for deposition of doped ceria ceramic and copper/doped ceria composite coatings on Ni substrates (foil and foam). The copper/doped ceria composites have potential value as protective functional coatings for current collectors in electrochemical cells including solid oxide fuel sells (SOFC). The doped ceria ceramic coating has potential application as a porous matrix for anodes of SOFCs operating on syngas, sour gas, or hydrocarbons.
Keywords Electrodeposition; Coating; Ceramics; Composite; Fuel cell

Effects of hydrogen on phase stability of ytterbium doped strontium cerates

Authors M. Matsuka, T. Sakai, H. Matsumoto, R.D. Braddock, I.E. Agranovski, T. Ishihara
Source
Materials Letters
Volume: 64, Issue: 7, Pages: 833-835
Time of Publication: 2010
Abstract The effect of hydrogen on the phase stability of both SrCe0.95Yb0.05O3 − α, (SCYb-5) powder and disk samples in both dry and wet hydrogen atmospheres was investigated. It was found that decomposition of the perovskite phase was especially evident in the disk samples treated in a dry hydrogen atmosphere, probably due to reduction of the tetravalent cerium ions to trivalent cerium ions in the sample. It was interesting to find that the extent of the decomposition of the perovskite phase was most influenced by the status (i.e. either disk or powder form) of the SCYb-5 samples, rather than the temperature or the extent of the reducing atmospheres. The findings of this study indicate that relaxation kinetics may play an important role in the phase stability of perovskite materials.
Keywords Ceramics; Perovskites; Phase stability; Hydrogen permeation

Electrical conductivity of the proton conductor BaZr0.9Y0.1O3-δ obtained by high temperature annealing

Authors Duval, S.B.C. / Holtappels, P. / Vogt, U.F. / Pomjakushina, E. / Conder, K. / Stimming, U. / Graule, T.
Source
Solid State Ionics, 178 (25)
Pages: p.1437-1441
Time of Publication: 2007

Trapping phosphate anions inside the [Ag4I]3+ framework: Structure, bonding, and properties of Ag4I(PO4)

Authors Oleneva, O.S. / Kirsanova, M.A. / Shestimerova, T.A. / Abramchuk, N.S. / Davliatshin, D.I. / Bykov, M.A. / Dikarev, E.V. / Shevelkov, A.V.
Source
Journal of Solid State Chemistry, 181 (1)
Pages: p.37-44
Time of Publication: 2008

GdBaCo2O5+x layered perovskite as an intermediate temperature solid oxide fuel cell cathode

Authors Tarancon, A. / Morata, A. / Dezanneau, G. / Skinner, S.J. / Kilner, J.A. / Estrade, S. / Hernandez-Ramirez, F. / Morante, J.R.
Source
as
Pages: p.255-263
Time of Publication: 2007

Effects of protons and acceptor substitution on the electrical conductivity of La6WO12

Authors Haugsrud, R. / Kjolseth, C
Source
Journal of Physics and Chemistry of Solids, 69 (7)
Pages: p.1758-1765
Time of Publication: 2008

Heavily doped oxygen-ion conducting Ln2 + xTi2 − xO7 − δ (Ln = Ho–Lu; x = 0.44–0.81) pyrochlores: Crystal structure, microstructure and electrical conductivity

Authors Shlyakhtina, A.V. / Savvin, S.N. / Levchenko, A.V. / Boguslavskii, M.V. / Shcherbakova, L.G.
Source
Solid State Ionics, 179 (21)
Pages: p.985-990
Time of Publication: 2008

Influence of microstructure on electrical properties in BaZr0.5In0.5O3-δ proton conductor

Authors Ahmed, I. / Eriksson, S.G. / Ahlberg, E. / Knee, C.S.
Source
Solid State Ionics, 179 (21)
Pages: p.1155-1160
Time of Publication: 2008

Effect of minor element addition on the electrical properties of BaZr0.9Y0.1O3

Authors Duval, S.B.C. / Holtappels, P. / Stimming, U. / Graule, T.
Source
Solid State Ionics, 179 (21)
Pages: p.1112-1115
Time of Publication: 2008

Varistor property of SnO2.CoO.Ta2O5 ceramic modified by barium and strontium

Authors Dhage, S.R. / Ravi, V. / Yang, O.B
Source
Journal of Alloys and Compounds, 466 (1)
Pages: p.483-487
Time of Publication: 2008

Plasma sprayed metal supported YSZ/Ni–LSGM–LSCF ITSOFC with nanostructured anode

Authors Hwang, C., Tsai, C.H., Lo, C.H., Sun, C.H.
Source
Journal of Power Sources, 180 (1),
Pages: p.132-142
Time of Publication: 2008

Comperative Seebeck Coefficient Measurements on Ceramic and Compacted Powder Column Samples; Case of ZnO

Authors Nataliya Sharova, Christian Kjlseth, Skjalg Erdal, Truls Norby
Source
Proceeding of the 1st Nordic School and Symposium on Functional Energy Related Materials
NorFERM-2008, 3-7 October 2008, Gol, Norway
Volume: R, Pages: 36
Time of Publication: 2008

Water vapor detection with individual tin oxide nanowires

Author F. Hernandez-Ramirez et al.
Source
Nanotechnology 18
Volume: 18, Issue: 424016 Time of Publication: 2007
Remark 4-point conductivity measurement on nanowire held in ProboStat in atmospheres with controlled humuidity

Measurement of oxygen exchange kinetics on thin-filmLa0.6Sr0.4CoO3-δ using non-linear electrochemical impedance spectroscopy

Authors J.R. Wilson, M. Sase, T. Kawada, S.B. Adler
Source
Electrochem. Solid State Lett.
Volume: 10, Issue: 5, Pages: B81-86
Time of Publication: 2007

Role of protons in the electrical conductivity of acceptor-doped BaPrO3, BaTbO3, and BaThO3

Authors K. A. Fury, R. Haugsrud, M. Hnsel, A. Magras, T. Norby
Source
Solid State Ionics
Volume: 178, Issue: 7-10, Pages: 461-467
Time of Publication: 2007
Remark Disk samples, impedance spectrocopy, transport number measurements

High-Temperature Proton Conductivity in Acceptor-Substituted Rare-Earth Ortho-Tantalates, LnTaO4

Authors R. Haugsrud, A. Tarancón, T. Norby, G. Dezanneau, A. Morata, F. Peiró, J.R. Morante
Source
J. Am. Ceram. Soc.
Volume: 90, Issue: 4, Pages: 1116-1121
Time of Publication: 2007
Remark Disk samples, impedance spectrocopy, transport number measurements

Mixed ionic and electronic conductivity of undoped and acceptor doped Er6WO12

Authors R. Haugsrud, H. Fjeld, K. R. Haug, T. Norby
Source
J. Electrochem. Soc.
Volume: 154, Issue: 1, Pages: B77-81
Time of Publication: 2007
Remark Disk samples, impedance spectrocopy, transport number measurements

Transport of hydrogen species in a single crystal SrTiO3

Authors M. Widere, R. Waser, J. B. Smith, T. Norby
Source
Solid State Ionics
Volume: 177, Pages: 1469-1476
Time of Publication: 2006
Remark Single crystal disk. Impedance spectrocopy, transport number measurements.

High-temperature proton conductivity in acceptor-doped LaNbO4

Authors R. Haugsrud, T. Norby
Source
Solid State Ionics
Volume: 177, Issue: 13-14, Pages: 1129-1135
Time of Publication: 2006
Remark Disk samples, impedance spectrocopy, transport number measurements

Ionic and Electronic Conductivity of 5% Ca-Doped GdNbO4

Authors R. Haugsrud, B. Ballesteros, M. Lira-Cant, T. Norby
Source
J. Electrochem. Soc.
Volume: 153, Issue: 8, Pages: J87-90
Time of Publication: 2006
Remark Disk samples, impedance spetroscopy

Pulsed laser deposition of high temperature protonic films

Authors F.W. Dynys, M.H. Berger, A. Sayir
Source
Solid State Ionics
Volume: 177, Issue: 26-32, Pages: 2333-2337
Time of Publication: 2006

Stoichiometric lanthanum chromite based ceramic inreconnects with low sintering temperature

Author Zhimin Zhong
Source
Solid State Ionics
Volume: 177, Issue: 7-8, Pages: 757-764
Time of Publication: 2006

Bismuth ruthenate based pyrochlores for IT-SOFC applications

Authors Zhong, Zhimin
Source
Electrochemical and Solid-State Letters
Volume: 9, Issue: 4, Pages: A215-219
Time of Publication: 2006

Proton conduction in rare earth ortho-niobates and ortho-tantalates

Authors R. Haugsrud, T. Norby
Source
Nature Materials
Volume: 5, Pages: 193-196
Time of Publication: 2006
Remark Link

On the steady state oxygen permeation through La2NiO4+d membranes

Authors J. B. Smith, T. Norby, J
Source
J. Electrochem. Soc.
Volume: 153, Issue: 2, Pages: A233-238
Time of Publication: 2006
Remark Oxygen permeation through disks sealed with Au gaskets. Analysis by MS.
Link

Proton conductivity of Ca-doped Tb2O3

Authors R. Haugsrud, Y. Larring, T. Norby
Source
Solid State Ionics
Volume: 176, Issue: 39-40, Pages: 2957-2961
Time of Publication: 2005
Remark Disk samples: 2-electrode AC conductivity & impedance spectroscopy vs T, transport number measurements of protons by EMF of concentration cells.

On the mixed ionic-electronic conductivity in Ca-doped La2Ti2O7

Authors R. Haugsrud, T. Norby
Source
Proc. 26th Ris Int. Symp. Mat. Sci. Solid State Electrochem, Ris Natl. Lab., Roskilde, Denmark
Pages: 209-214
Time of Publication: 2005
Editors S. Linderoth, A. Smith, N. Bonanos, A. Hagen, L. Mikkelsen, K. Kammer, D. Lybye, P.V. Hendriksen, F.W. Poulsen, M. Mogensen, W.G. Wang
Remark Disk samples: 2-electrode AC conductivity & impedance spectroscopy vs T, transport number measurements of protons and oxygen ions by EMF of concentration cells.
Link

Sensor Letters 3

Source
Sensor Letters 3
Volume: 3, Pages: 258-262
Time of Publication: 2005
Remark Link

J.Phys. and Chem. Solids

Source
J.Phys. and Chem. Solids
Pages: 7878-7882
Time of Publication: 2005

Sensors and Actuators

Source
B 106
Issue: 837-842 Time of Publication: 2005

Temperature dependence of oxygen ion transport in Sr+Mg substituted LaGaO3 (LSGM) with varying grain sizes

Authors C. Haavik, E.M. Ottesen, K. Nomura, J.A. Kilner, T. Norby, Solid State Ionics, 174 [1-2] (2004) 233-43.
Source
Solid State Ionics
Volume: 174, Issue: 1-2, Pages: 233-243
Time of Publication: 2004
Remark Disk samples: 2-electrode and 4-point (van der Pauw) AC conductivity & impedance spectroscopy vs T, use of surface guard.

Transport numbers from hydrogen concentration cells over different oxides under oxidising and reducing conditions

Authors M. Widere, N. Kochetova, T. Norby
Source
Pages: 3147-3151
Time of Publication: 2004
Remark Disk samples: 2-electrode AC conductivity, transport numbers of hydrogen ions by EMF of hydrogen concentration cell

Conductivity dependence on oxygen partial pressure and oxide-ion transport numbers determination for La2Mo2O9

Authors A. Tarancn, T. Norby, G. Dezanneau, A. Morata, F. Peir, J.R. Morante
Source
Electrochemical and Solid-State Letters
Volume: 10, Issue: 7, Pages: A373-375
Time of Publication: 2004
Remark Disk samples: 4-point van der Pauw conductivity, 2-electrode impedance spectroscopy, transport numbers of oxygen ions by EMF of oxygen concentration cell

Impedance spectroscopy and proton transport number measurements on Sr-substituted LaPO4 prepared by combustion synthesis

Authors S. Gallini, M. Hnsel, T. Norby, M.T. Colomer, J.R. Jurado
Source
Solid State Ionics
Volume: 162-163, Pages: 167-173
Time of Publication: 2003
Remark Disk samples: 2-electrode AC conductivity, transport numbers of protons by EMF of hydrogen concentration cell

HT Corrosion of a Cr-5wt%Fe1wt%Y2O3 Alloy and Conductivity of the Oxide Scale

Authors Y. Larring, R. Haugsrud, T. Norby, J. Electrochem. Soc., 150 [8] (2003) B374-79
Source
J. Electrochem. Soc.
Volume: 150, Issue: 8, Pages: B374-379
Time of Publication: 2003
Remark Disk samples of alloy, with gold contact outside one oxide layer.

Proton and apparent hydride ion conductivity in Al-substituted SrTiO3

Authors M. Widere, W. Mnch, Y. Larring, T. Norby
Source
Solid State Ionics
Volume: 154-155, Pages: 669-677
Time of Publication: 2002
Remark Disk samples, 2-electrodes, Au seal, AC conductivity and concentration cell/EMF measurements of transport numbers for hydrogen and oxygen ions

Water and protons in electrodeposited MnO2 (EMD)

Authors S.W. Donne, F.H. Feddrix, R. Glckner, S. Marion, T. Norby
Source
Solid State Ionics
Volume: 152-153, Pages: 695-701
Time of Publication: 2002
Remark Disk samples, 2 electrodes, AC conductivity and concentration cell/EMF measurements of transport numbers for protons. RT-100C.

Hydrogen ion conduction in iron substituted strontium titanate, in SrTi1-xFexO3-x/2 (0 x 0.8)

Authors S. Steinsvik, Y. Larring, T. Norby
Source
Solid State Ionics
Volume: 143, Issue: 1, Pages: 103-116
Time of Publication: 2001
Remark Disk samples, 2-electrodes, AC conductivity and concentration cell/EMF measurements of transport numbers for hydrogen and oxygen ions

"Spinel and perovskite functional layers between Plansee metallic interconnect (Cr-5wt%Fe-1wt%Y2O3) and ceramic (La0.85Sr0.15)0.91MnO3 cathode materials for solid oxide fuel cells"

Authors Y. Larring, T. Norby
Source
J. Electrochem. Soc.
Volume: 147 , Issue: 9, Pages: 3251-3256
Time of Publication: 2000
Remark Disk samples of alloy + LSM layer

Phase relations, chemical diffusion and electrical conductivity in pure and doped Sr4Fe6O13 mixed conductor materials

Authors R. Bredesen, T. Norby, A. Bardal, V. Lynum
Source
Solid State Ionics
Volume: 135, Pages: 687-697
Time of Publication: 200
Remark Disk sample, 4-point van der Pauw conductivity measurements

Thermoelectric power of the mixed ionic-electronic conductor SrTi0.8Fe0.2O3-d in various atmospheres

Authors T. Norby, S. Steinsvik
Source
proc. Nordic Energy Research Workshop on "Hydrogen in Electrochemical Energy Conversion", Geilo
Volume: March 1999 Time of Publication: 1999
thermoelectric
Editors F.W. Poulsen, R.J. Aaberg
Remark Bar sample, thermoelectric power (Seebeck coefficient) measurements

La1-xBaxCr1-yTiyO3 with varied oxygen content

Authors P. Karen,T. Norby
Source
J. Electrochem. Soc.
Pages: 264-269
Time of Publication: 1998
Remark Disk sample, 4-point van der Pauw conductivity measurements using Au contacts

Electrochemical behaviour of Ni/YSZ electrodes

Author T. Norby
Source
Proc. 2nd European SOFC Forum
Volume: May 1996 , Pages: 607-616
Time of Publication: 1996
Editor B. Thorstensen
Remark Disk samples, 3 electrodes (Working, counter, ring reference)

Hydrogen isotope effects on Ni/YSZ electrodes

Authors T. Norby, P. Kofstad
Source
Proc. 17th Ris Int. Symp. on Materials Science: High Temperature Electrochemistry: Ceramics and Metals
Ris Natl. Lab., Roskilde, Denmark (1996)
Pages: 381-386
Time of Publication: 1996
Editors F.W. Poulsen, N. Bonanos, S. Linderoth, M. Mogensen and B. Zachau-Christiansen
Remark Disk samples, 3 electrodes (Working, counter, ring reference)

Ageing of YSZ electrolytes at 800C

Authors T. Norby, P.A. Osborg, H. Rder
Source
Proc. 2nd European SOFC Forum
Volume: May 1996, Pages: 315-320
Time of Publication: 1996
Editor B. Thorstensen
Remark Disk samples, 4 stacked and measured simultaneously, with Pt electrodes in-between.

Proton conduction in Ca- and Sr-substituted LaPO4

Authors T. Norby, N. Christiansen, Solid State Ionics
Source
Solid State Ionics
Volume: 77, Pages: 240-243
Time of Publication: 1995
Remark Bar samples, 4-point AC conductivity measurements

Proton and deuteron conductivity in CsHSO4 and CsDSO4 by in situ isotopic exchange

Authors T. Norby, M. Friesel, B.-E. Mellander
Source
Solid State Ionics
Volume: 77, Pages: 105--110
Time of Publication: 1995
Remark Disk sample, 4-point van der Pauw measurements

Oxidation of methane on a SrFeO3/Au//YSZ electrode characterised by mass spectroscopy and 18O2 pulses

Authors T. Norby, H. Middleton, E.W. Hansen, I. Dahl, A.G. Andersen
Source
Chem. Eng. Technol.
Volume: 18, Pages: 139-147
Time of Publication: 1995
Remark Disk samples, sealed onto support, with electrodes for electrochemical pumping. Exctract to MS directly from electrodes by silica tubes.

Ageing of YSZ electrolytes at 1000C

Authors T. Norby, P.A. Osborg and H. Rder
Source
Proc. 1st European SOFC Forum
Volume: Oct. 1994, Pages: 671-679
Time of Publication: 1994
Editor U. Bossel
Remark Disk samples, 4 stacked and measured simultaneously over 40 days, with Pt electrodes in-between

Oxidation of CH4 on La0.7Ca0.3CrO3//YSZ anodes

Authors T. Norby, R. Hildrum, M. Seiersten, R. Glenne, P.A. Osborg and O. Dyrlie
Source
Proc. 1st European SOFC Forum
Volume: Oct. 1994, Pages: 217-226
Time of Publication: 1994
Editor U. Bossel
Remark Disk samples, sealed by glass onto support, fuel cell and electrochemical pumping modes, MS analysis of gases.

Protons in LaErO3

Author Y. Larring and T. Norby
Source
Solid State Ionics
Volume: 70/71, Pages: 305-310
Time of Publication: 1994
Remark Disk samples, 2 electrodes, EMF transport number and AC conductivity measurements

Electrical conductivity and ionic transport number of YSZ and Cr-doped YSZ single crystals at 200-1000C

Authors T. Norby, M. Hartmanov
Source
Solid State Ionics
Volume: 67, Pages: 57-64
Time of Publication: 1993
Remark Small single crystals, Pt paint electrodes, placed over small hole in support plate to form concentration cell. Role of sample holder parasitic conductance evaluated.

Reaction resistance in relation to three phase boundary length of Ni/YSZ electrodes

Authors T. Norby, O.J. Velle, H. Leth-Olsen, R. Tunold, S.C. Singhal, H. Iwahara, eds.
Source
Electrochem. Soc. Proc.
Volume: 93-4, Pages: 473-477
Time of Publication: 1993
Remark Disk sample, 3-electrode setup, patterned working electrode

Protonic conduction in acceptor-doped cubic rare earth sesquioxides

Authors T. Norby, O. Dyrlie, P. Kofstad
Source
J. Am. Ceram. Soc.
Volume: 75 , Pages: 1176-1181
Time of Publication: 1992
Remark Disk samples, AC conductivity and EMF transport numbers (protons and oxygen ions). Nice schematic of sample arrangement.

The electrode system O2/Pt//ZrO2:8Y2O3 investigated by impedance spectroscopy

Authors O. J. Velle, T. Norby, P. Kofstad
Source
Solid State Ionics
Volume: 47, Pages: 161-167
Time of Publication: 1991
Remark Thin electrolyte disk with 3 Pt electrodes. NOTE: probable reference electrode problem with such a thin electrolyte.

Electronic, Ionic and Protonic Conductivities of a Commercial, Polycrystalline a-Al2O3

Authors T. Norby, P. Kofstad
Source
High Temp.-High Press.
Volume: 20, Issue: 3, Pages: 345-360
Time of Publication: 1988
Remark Closed alumina support tube used as sample. AC conductivity, impedance spectroscopy, EMF transport number measurements, long-term measurements at 1400C.

Proton and Native-Ion Conductivities of Y2O3 at High Temperatures

Authors T. Norby, P. Kofstad
Source
Solid State Ionics
Volume: 20, Pages: 169-184
Time of Publication: 1986
Remark Disk sample: 2-electrode AC conductivity, transport numbers of protons and oxygen ions by EMF of concentration cells

Electrical Conductivity and Defect Structure of Y2O3 as a Function of Water Vapor Pressure

Authors T. Norby, P. Kofstad
Source
J. Am. Ceram. Soc.
Volume: 67, Issue: 12, Pages: 786-792
Time of Publication: 1984
Remark 5 disk samples stacked and measured simultaneously (2-electrode AC conductivity)
norecs.com

This article is the property of its author, please do not redistribute or use elsewhere without checking with the author.