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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
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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
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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
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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

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
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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
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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
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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
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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
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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
norecs.com

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