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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 Jouttijärvi, 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, Raphaël 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 Mössbauer 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. Mössbauer 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 S·cm−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 ppm·K−1 overall.
Keywords Ruddlesden–Popper structure; oxygen non-stoichiometry; crystal structure; Mössbauer spectroscopy; electrical conductivity; thermal expansion
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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 16.1±11.7 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, Thorbjørn 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
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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
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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. Jouttijärvi, 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 Tarancón, 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 W·cm–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
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Influence of annealing at intermediate temperature on oxygen transport kinetics of Pr2NiO4+δ

Authors Saim Saher, Jia Song, Vaibhav Vibhu, Clément Nicollet, Aurélien 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
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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
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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
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