bluuebunny/crossref_metadata_2025 huggingface dataset:
Soft X-Ray Absorption and Photoemission Study on the Electronic Structure of (La,Sr)CoO3
Authors: Miyoshi Shogo , Yamaguchi Shu
Published: July 2015

In order to reveal the electronic structure of (La,Sr)CoO3-d
relevant to the chemistry in SOFC cathode, soft x-ray absorption and photoemission spectroscopy were employed. The lowest energy component in O K-edge XAS spectra of the La0.6Sr0.4CoO3-d
is ascribed to the electron holes introduced by Sr-doping, and sensitively changes in intensity with oxygen nonstoichiometry. On the other hand, the Co2p XAS spectrum is insensitive to the oxidation state of the specimen. The increase in oxygen nonstoichiometry is accompanied with upward shift of the Fermi energy, while the binding energy of the Co2p level is almost unchanged. It is suggested that the relevant electron holes are rather associated with oxide ion rather than simple unoccupied state of cobalt ion.
Quantifying Chemical Expansion of Non-Stoichiometric Oxide Thin Films: Challenges and Opportunities
Authors: Swallow Jessica G. , Kim Jae Jin , Chen Di , Bishop Sean R. , Smith James F. , Tuller Harry L. , Van Vliet Krystyn J.
Published: July 2015

Non-stoichiometric oxides within active components of solid oxide fuel cells (SOFCs) can exhibit chemical expansion, including measurable changes in lattice parameter or volume as a function of point defect concentrations. Robust SOFC design requires knowledge of how chemical expansion contributes to mechanical strains at interfaces that can promote dislocation mobility, delamination, or fracture. Direct measurement of chemical expansion via X-ray diffraction or dilatometry typically requires long time scales (minutes to hours) to allow equilibration of gas atmospheres or bulk samples, or to allow adequate signal detection in the absence of synchrotron access. Here, we discuss current methods of measuring chemical expansion in situ and consider how they may be extended to investigate the expansion of thin films or fuel cell stacks. A facile approach to measuring dynamic chemical expansion under in operando conditions of SOFC electrodes could facilitate improved design of materials that withstand large chemomechanical changes during SOFC operations.
Understanding the Operating Mechanisms of Mixed Ionic Electronic Conductors: From Synchrotron-Based 3D Reconstruction to Electrochemical Characterization and Modeling
Authors: Hubert Maxime , Laurencin Jérôme , Cloetens Peter , Couturier Karine , Lefebvre-Joud Florence , Bleuet Pierre , Siebert Elisabeth
Published: July 2015

A model describing the operation of a Mixed Ionic Electronic conductor (MIEC) has been developed. The main mechanisms and transport phenomena are taken into account. Thanks to a 3D reconstruction obtained by nano-holotomography on a sample prepared with a Plasma Focused Ion Beam (PFIB), the real electrode microstructure has been used into the model. The role of electrode microstructural properties on performances has been estimated through a sensitivity analysis. As the reactive pathways are different in both polarizations, the impact of morphological properties is not the same according to the operating mode. The electrode specific surface area has an effect on the performances and the ratio of the volume fraction to the tortuosity factor of the solid phase has an impact on the electrode response only in cathodic polarization.
Quantitative Evaluation of Electrochemically Active Area in an SOFC Cathode by Oxygen Isotopic Exchange Measurements of a Model Patterned Electrode
Authors: Fujimaki Yoshinobu , Nakamura Takashi , Bagarinao Katherine Develos- , Yamaji Katsuhiko , Yashiro Keiji , Kawada Tatsuya , Iguchi Fumitada , Yugami Hiroo , Amezawa Koji
Published: July 2015

The electrochemically active area in an SOFC cathode was quantitatively evaluated from 18O/16O isotope exchange with/without polarization and following isotopic distribution analysis by second ion mass spectroscopy. For this purpose, we proposed a patterned dense thin film electrode modelling a columnar SOFC cathode, and was fabricated it with La0.6Sr0.4CoO3-δ
on a Ce0.9Gd0.1O1.95-δ
electrolyte. Compared with the results under open circuit condition, the increase in the isotopic ratio of 18O was observed near the electrode/electrolyte interface when a cathodic bias was applied. Such an increase in the 18O isotopic ratio was considered due to the electrochemical oxygen incorporation. The electrochemically active area was evaluated as approximately 25 μm in the La0.6Sr0.4CoO3-δ
patterned thin film electrode under cathodic polarization of 220 mV in P(O2) = 1 bar at 973 K.
Confidence Limits in the Oxygen Transport Parameters of the (La0.8Sr0.2)(Cr0.2Fe0.8)O3-δ Determined By the Isotopic Exchange, Depth Profiling Method
Authors: Chater Richard John
Published: July 2015

The polycrystalline oxide (La0.8Sr0.2)(Cr0.2Fe0.8)O3-
d is a mixed ionic and electronic conductor of a type called “acceptor-doped transition metal oxide” that has been explored for application as an electrode material in SOFC and other electrochemical devices working at intermediate to high temperatures (500°C to 900°C). The isotopic exchange, depth profiling method allows both bulk oxygen transport parameters, the diffusion coefficient, D(T) and surface reaction coefficient, k(T), to be determined simultaneously once an appropriate solution of the diffusion equation has been identified. Error assessment of (D,k) through the numerical fit process is quantified for the variances that are used as weights in extracting the transport activation energies from the corresponding Arrhenius plots. As the dataset is generally small for a single anneal ambient composition, standard statistical F and t-tests are used and the 95% confidence limits reported that are essential for comparison between datasets.
Theoretical Study on Oxygen Dissociation Reaction on LaSrCoO3
Authors: Ishimoto Takayoshi , Sato Kenji , Tada Tomofumi , Amezawa Koji , Koyama Michihisa
Published: July 2015

Doped lanthanum cobaltite and its derivatives are used as cathode materials in solid oxide fuel cell. It is expected that the high catalytic materials for oxygen adsorption and dissociation on oxide surface are found by the controlling the electronic structure of doped lanthanum cobaltite. In this study, we analyzed the stability of oxygen vacancy and surface reaction of oxygen under different spin states of Co ion in Sr doped LaCoO3 by using density functional theory. We clearly found that the difference of oxygen vacancy position and spin state of Co ion affects the reactivity of oxygen on surface.
Evaluation of Exchange Current Density for LSM Porous Cathode Based on Measurement of Three-Phase Boundary Length
Authors: Miyoshi Kota , Miyamae Takuma , Iwai Hiroshi , Saito Motohiro , Kishimoto Masashi , Yoshida Hideo
Published: July 2015

Here we propose an empirical formula for the exchange current density per unit TPB (three-phase boundary) length for porous LSM (lanthanum strontium manganite) cathodes for solid oxide fuel cells, which is often required for numerical modeling of cathode performance based on reconstructed microstructures obtained with tomography techniques. Electrochemical measurement of LSM cathodes was conducted under various oxygen partial pressure (0.05-0.25 atm) and temperature (800-950 °C) conditions. The derived values were compared with those from a thin and dense patterned LSM electrode in literature, and were found to be small at 800 °C. One of the possible reasons is that the charge transfer can be occurred at not only TPB but also two-phase (LSM-Pore) boundary in the case of thin patterned electrode.
In-Situ Surface Analysis of SOFC Cathode Degradation Using High Temperature Environmental Scanning Electron Microscopy
Authors: Niania Mathew , Podor Renaud , Skinner Stephen J. , Kilner John A.
Published: July 2015

In this study the surface properties of LSCF have been studied in in-situ from room temperature to 1000oC using a High Temperature Environmental Scanning Electron Microscope (HT-ESEM) under a number of different atmospheres. Dense, polished La0.6Sr0.4Co0.2Fe0.8O3-
δ (LSCF) was observed during thermal annealing under a vacuum, pure oxygen, pure water and humid air atmospheres. The effect each atmosphere had on the surface morphology has been characterized in real time and analysed chemically using EDX. Significant differences in the surface behaviour were seen under each atmosphere. The results observed in the HT-ESEM were complimentary to in-operando surface exchange measurements and have enabled a more detailed understanding of SOFC cathode decomposition.
Changes in SOFC Cathode Crystallographic Structure Induced by Temperature, Potential and Oxygen Partial Pressure Studied Using in-Situ HT-XRD
Authors: Kivi Indrek , Aruväli Jaan , Kirsimäe Kalle , Heinsaar Alar , Nurk Gunnar , Lust Enn
Published: July 2015

Porous and monolithic La0.6Sr0.4Co3
−δ, Gd0.15Sr0.85CoO3
−δ and La0.6Sr0.4MnO3
−δ cathodes for intermediate temperature solid oxide fuel cell applications have been studied at different cathode potentials and at different oxygen partial pressures using high-temperature in situ XRD (HT-XRD) method. The kinetic response of the crystallographic structure and lattice parameters on the changes of electrode potential has been correlated with the chronoamperometric data and discussed. Reversible changes in the lattice parameters were observed depending on the temperature (T), electrode potential (E) and oxygen partial pressure (pO2) applied. At fixed T and pO2, the cathode potential noticeably influences the unit cell volume, thus, the oxygen stoichiometry and concentration of vacancies. The La0.6Sr0.4MnO3
-δ cathode does not have remarkable crystallographic changes under comparable conditions. Influence of the cathode potential on the unit cell volume was more pronounced at lower pO2.
Surface Segregation Phenomena in La0.6Sr0.4Co0.2Fe0.8O3-δ Subjected to Mechanical Stress
Authors: Araki Wakako , Tanii Wataru , Arai Yoshio
Published: July 2015

In the present study, Sr surface segregation phenomena in La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) subjected to mechanical stress were investigated. LSCF specimens were mirror-polished and annealed under uniaxial compression or four-point bending. The polished surfaces before and after the annealing were characterized with a scanning electron microscope. In the uniaxial compression case, the number of the segregated particle is fewer but the particle size is larger for the compressed sample. In the case of four-point bending, a more significant segregation was observed on the tensile side than on the compressive side, whilst there is least segregation observed on the stress-free surface near the edges, which could be related to a stress gradient through thickness. The observation result indicates, therefore, that the surface segregation in LSCF could be controlled by applying mechanical stress.
Electrochemical Performance of Solid Oxide Cell Oxygen Electrodes Under Pressurization
Authors: Hughes Gareth , Railsback Justin , Butts Danielle , Barnett Scott A
Published: July 2015

The solid oxide cell (SOC) composite oxygen electrodes (La0.8Sr0.2)0.98MnO3-δ - Zr0.84Y0.16O2-γ (LSM-YSZ) and La0.6Sr0.4Fe0.8Co0.2O3-d (LSCF) - Ce0.8Gd0.2O1.95 (LSCF-GDC) were studied at oxygen partial pressure pO2 from 0.1 to 10 atm by impedance spectroscopy. Two primary responses were observed in the impedance spectra, which were fit using an equivalent circuit model with two RQ elements. A higher frequency response observed at ~ 103 Hz varied as pO2
-0.25. A lower frequency response observed at ~ 10 to 100 Hz varied as pO2
-0.15. Total electrode resistances decreased with increasing pO2 following a pO2
-0.17 dependence for LSM-YSZ and a pO2
-0.20 dependence for LSCF-GDC. Overall, the area-specific resistance of these SOC oxygen electrodes is reduced by a factor of ~2 by increasing oxygen pressure from a nominal 0.2 atm (air) to 10 atm, thereby improving pressurized SOC performance.
Fundamental Impact of Humidity on SOFC Cathode Degradation
Authors: Huang Yi-Lin , Pellegrinelli Christopher , Wachsman Eric D.
Published: July 2015

The durability of SOFCs under real working conditions is still an issue for commercial deployment. In particular cathode exposure to atmospheric air contaminants, such as humidity, can result in long-term performance degradation issues. Therefore, a fundamental understanding of the interaction between water molecules and cathodes is essential to resolve this issue and further enhance cathode durability. To study the effects of humidity on the ORR, we used insitu 18O isotope exchange techniques to probe the exchange of water with two of the most common SOFC cathode materials, LSM and LSCF. In this experiment, heavy water, D2O (mass/charge ratio of m/z=20), is used to avoid overlapping of H2O and 18O2 cracking fraction (m/z=18). Temperature programmed isotope exchange measurements were performed to comprehensively study the interaction of water with the cathode surface as a function of temperature, oxygen partial pressure, and water vapor concentration. The results suggest that H2O and O2 share the same surface exchange sites. Therefore, the presence of H2O competes with O2 for the available surface sites. Our findings show that H2O prefers to exchange with LSM and LSCF at a lower temperature, ~300-450°C. For LSM, O2 is more favorable than H2O to be adsorbed on LSM surface and the presence of O2 limits H2O exchange with LSM. H2O has two different exchange mechanisms to react with the LSCF surface, and each mechanism dominates in a different temperature region. The data are summarized to a Temperature-PO2 diagram to visualize the dominant reactions at temperature and PO2 for the two cathode materials.
An Elementary Kinetic Model for the Electrochemical Reduction of Oxygen on LSM/YSZ Composite Cathodes
Authors: Banerjee Aayan , Deutschmann Olaf
Published: July 2015

A computational half-cell model was developed to study the coupled interactions of species, electron and ion transport through porous media in addition to surface and electro-chemistry. Surface and electro-chemistry were represented using an elementary kinetic model. The model was validated against LSM/8YSZ composite cathode measurements made by Barbucci et al. [Electrochimica Acta, 47(13-14), 2183–2188 (2002)] to obtain realistic electrochemical parameters. The versatility of the micro-kinetic oxygen reduction mechanism was evaluated by predicting the performance of a pure LSM cathode. The simulated results were found to be in good agreement with measured data. A sensitivity analysis revealed that at high temperatures, ohmic resistance in the electrolyte and surface ionization of adsorbed oxygen atoms were the rate-limiting processes. At lower temperatures, dissociation of molecular oxygen adsorbed on the LSM surface and ion transfer at the LSM/YSZ interface were also found to be rate-limiting.
Surface Modification of La0.6Sr0.4Co0.2Fe0.8O3-δ Cathode by Atomic Layer Deposition of La0.6Sr0.4CoO3-δ for High-Performance Solid Oxide Fuel Cells
Authors: Choi Hyung Jong , Bae Kiho , Jang Dong Young , Park Suk Won , Han Gwon Deok , Shim Joon Hyung
Published: July 2015

Surface modification of La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) was conducted by atomic layer deposition (ALD) with La0.6Sr0.4CoO3-δ (LSC). The anode supported cell with LSC modified LSCF cathode was used to analyze the effect of ALD LSC treatment. At the cell operating temperature (600oC) with the cell voltage of 550 mV, ALD treated cell has power density of 206.6 mW cm-2 and showed increase in performance by 15.8 mW cm-2 compared to bare cell. By analyzing the impedance results, it was found that both adsorption (or surface diffusion) and charge transfer kinetics were enhanced after ALD surface modification.
Thermodynamic Stability Assessment of MIEC Cathode Materials for Solid Oxide Fuel Cells
Authors: Cetin Deniz , Yu Yang , Luo Heng , Lin Xi , Pal Uday Bhanu , Basu Soumendra Nath , Gopalan Srikanth
Published: July 2015

Promising electrochemical performance of mixed ionic-electronic conductors (MIEC) such as La(1-x)SrxCo0.2Fe0.8O3-δ (LSCF,where x=0.2, 0.3, 0.4), Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF 5582), GdBaCo2O6-δ (GBCO), and PrBaCo2O6-δ (PBCO) make these materials potentially excellent candidates for SOFC applications. However, in order to consider these materials for cathode application in SOFC stacks, their long-term thermodynamic stability in the operating environment of SOFCs, including unexpected and uncommon situations such as CO2-leakage from the anodic side should be thoroughly considered. This study investigates the thermodynamic stability of promising SOFC cathodes under operating conditions, in molten salt media, and through galvanic cell experiments. The cathode materials of interest are La(1-x)SrxCo0.2Fe0.8O3-δ (LSCF, where x=0.2, 0.3, 0.4), Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF 5582), GdBaCo2O6-δ (GBCO), and PrBaCo2O6-δ (PBCO). The stability of these materials is studied in air and at various CO2 partial pressures.
An Interfacial Nanospike-Structured Cathode for Low Temperature Solid Oxide Fuel Cells
Authors: Ding Hanping , Xue Xingjian
Published: July 2015

Lowering operating temperatures is a promising strategy to improve the durability and reduce the cost of solid oxide fuel cell (SOFC) systems. However, the ohmic and polarization resistance would increase significantly at low temperatures, particularly that of cathode electrode due to sluggish oxygen reduction reactions. To reduce polarization loss at low temperatures, cathode materials have been studied extensively. The high performance cathode electrodes were also obtained through nano-scale engineering enabled by infiltration technique. Here we report the fabrication and evaluation of a novel interfacial nanospike-structured cathode. The growth of interfacial nanospikes on the pore walls of the cathode was enabled by a discharge treatment under low-temperature sintering process. The electrochemical performance of the corresponding button cells was well demonstrated at low operating temperatures of 350-550 oC. The stability of interfacial nanospikes was also examined under thermal-cycling conditions.
Characterization of the Contact Resistance of Cathodic SOFC Contacting
Authors: Udomsilp David , Roehrens Daniel , Menzler Norbert H. , Conradt Reinhard , Guillon Olivier
Published: July 2015

DC conductivity experiments were carried out in order to characterize the area specific resistances (ASR) of various multi-layer-structures. They represent the contacting interface between cathode and interconnector of state-of-the-art planar anode-supported SOFCs. The investigation focused on quantifying the influence of various chromium evaporation protection layer materials (MnOx, MnCo1.9Fe0.1O4 (MCF)), perovskitic cathode contact layers (LCC10, LCC12, LSCF), operational parameters during stack joining and the effect of pre-annealing of multi-layer samples on the overall ASR of the model system. The results demonstrate the influence of different material combinations as well as the duration of heat treatment during the joining process on the cell resistance, whereas we have not observed an obvious effect of pre-annealing.
Microstructure and Polarization characteristics of LSCF-GDC Composite Cathode with Different Volume Fractions
Authors: Kim Y. T. , Ohi Akihiro , He An , Jiao Zhenjun , Shimura Takaaki , Klotz Dino , Hara Shotaro , Shikazono Naoki
Published: July 2015

In the present study, La0.6Sr0.4Co0.2Fe0.8O3 (LSCF)-Gd0.1Ce0.9O1.95 (GDC) composite cathodes with different volume fractions were fabricated by the screen printing method, and their polarization characteristics and microstructure parameters are evaluated. Cathode overpotentials were measured at the measurement condition of 700 °C and 100 % O2. Microstructures were reconstructed by focused ion beam-scanning electron microscope (FIB-SEM). The relationship between polarization characteristics and microstructure is quantitatively investigated.
High-Performance Cathode/Electrolyte Interfaces for SOFC
Authors: Szász Julian , Wankmüller Florian , Wilde Virginia , Störmer Heike , Gerthsen Dagmar , Menzler Norbert H. , Ivers-Tiffée Ellen
Published: July 2015

High-performance oxygen electrodes for solid oxide fuel cells (SOFC) require a highly efficient material selection for the oxygen reduction reaction that takes places near the cathode/electrolyte interface. La1-xSrxCo1-yFeyO3-δ (LSCF) delivers fast oxygen-exchange kinetics and is therefore utilized as cathode material for high performing state-of-the-art anode-supported fuel cells. The main disadvantage of LSCF is its instability against Zr-based electrolytes. A diffusion barrier interlayer consisting of Gd doped cerium oxide (GDC) is therefore inserted to prevent the formation of an insulating SrZrO3 phase. This study presents new results on the importance of the GDC manufacturing conditions. A complex interaction of GDC with LSCF and YSZ during fabrication is found with a tremendous influence on the performance of the cathode/electrolyte interface of SOFCs.
Investigating the Relationship between Operating Conditions and SOFC Cathode Degradation
Authors: Pellegrinelli Christopher , Huang Yi-Lin , Taillon Joshua A. , Salamanca-Riba Lourdes G. , Wachsman Eric D.
Published: July 2015

Polarization losses associated with the cathode oxygen reduction reaction and degradation of cathode materials remain as hurdles for widespread implementation of solid oxide fuel cells (SOFC). Rates of degradation depend significantly on the operating temperature and gas conditions, such as the presence of unwanted oxygen- containing compounds, namely H2O and CO2. In this study we explore degradation mechanisms for a common composite cathode material, La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) - Ce0.90Gd0.10O1.95 (GDC). Three-electrode cells have been tested under various temperatures, PO2s and contaminant conditions in order to observe changes through electrochemical impedance spectroscopy (EIS). EIS is a powerful tool, which allows us to identify changes in the reaction steps comprising the overall ORR. Our EIS results indicate a strong correlation between blocking effects, caused by CO2 and H2O, and the operating temperature of the cell. Using EIS to de- convolute the overall cathode polarization helps to identify the mechanisms by which degradation occurs.
Solid Oxide Steam Electrolysis Anodes with Precisely Controlled Microstructure for Performance Analysis
Authors: Clancy Graeme C. , Peppley Brant A. , Pharoah Jon G. , Ryland Donald
Published: July 2015

Understanding the effect of oxygen electrode structure on electrochemical performance of a solid oxide electrolysis cell is of great importance, especially considering oxygen electrode delamination issues that are presently limiting their commercialization. To study the structure-performance relationship a closely managed production method has been developed to create controlled and repeatable electrode structures. The electrode deposition method uses a solvent based ink sprayed using an air brush. The ink formulation, processing, and deposition have been strictly controlled. The sintering method chosen to calcine the structure was carefully constrained. Morphological differences caused by the adjustment to the ink formulation, spraying, and sintering parameters were observed.
Chromium Deposition and Poisoning of LSCF and LSM Oxygen Electrodes of Solid Oxide Electrolysis Cells
Authors: Chen Kongfa , Bo Wei , Hyodo Junji , Ishihara Tatsumi , Jiang San Ping
Published: July 2015

The degradation of solid oxide electrolysis cells (SOECs) is an issue of both scientific and technical importance. In this study, chromium deposition and poisoning at La0.6Sr0.4Co0.2Fe0.8O3-
d (LSCF) and La0.8Sr0.2MnO3+
d (LSM) oxygen electrodes are studied under SOEC operation conditions at 800 oC. Performance degradation was observed for the reaction in the presence of Fe-Cr alloy metallic interconnect. The results indicate the deposition of SrCrO4, CrO2.5 and Cr2O3 phases on the surface of LSCF oxygen electrodes and YSZ electrolyte surface and on the LSM electrode inner surface. Cr deposition is closely related to the increased segregation of SrO species under anodic polarization conditions.
Surface Oxygen Exchange Properties of Sr Doped La2NiO4+δ as SOFC Cathode: Thin-Film Electrical Conductivity Relaxation Investigation
Authors: Guan Bo , Li Wenyuan , Zhang Xinxin , Liu Xingbo
Published: July 2015

La2-xSrxNiO4+δ dense films are prepared by a novel spray-modified pressing method. The surface reaction kinetics is investigated via electrical conductivity relaxation (ECR). The layer thickness, 5~10 μm, is much less than the characteristic length of lanthanum nickelates, resulting in surface-controlled situation and allowing more accurate fitting than the traditional pellets ECR on the surface exchange coefficient (k). k for LNO is 1.6×10-5 cm/s in 0.2 atm at 700oC. Sr doping impairs the exchange kinetics, and k of Sr40 is about one order of magnitude smaller than undoped one. Interstitial oxygen and Ni oxidation state are suggested the predominant roles in determining surface kinetics. Given the properties of the thin-film herein developed by spray-modified pressing is closer to those in practical porous electrode compared to pulsed laser deposited film in terms of preferential orientation and strain, it warrants the use of such a method in a variety of pertinent investigations.
Effect of Nature of the Ceramic Component of the Composite Electrodes Based on La1.7Ca(Sr)0.3NiO4+δ on Their Electrochemical Performance
Authors: Pikalova E. , Bogdanovich N. , Kolchugin A. , Brouzgou A. , Bronin D. , Plaksin Sergey Vladimirovich , Khasanov A. , Tsiakaras P.
Published: July 2015

The manuscript focuses on the electrochemical performance of the La1.7Ca0.3NiO4+δ (LCNO) and La1.7Sr0.3NiO4+δ (LSNO) based composite cathodes with Ce0.8Sm0.2O1.9 (SDC) or BaCe0.89Gd0.1Cu0.01O3 (BCGCu) ceramic components in contact with BCGCu or BaCe0.5Zr0.3Y0.2O3+1wt.%CuO (BCZYCu) proton conducting electrolytes in comparison with La0.6Sr0.4Fe0.8Co0.2O3 (LSFC) and La0.75Sr0.2MnO3 (LSM) composite cathodes.
Ln2NiO4+δ
(Ln = La, Pr) As Suitable Cathodes for Metal Supported Cells
Authors: Rougier Aline D. , Flura Aurélien , Nicollet Clément , Vibhu Vaibhav , Fourcade Sébastien , Lebraud Eric , Bassat Jean-Marc , Grenier Jean-Claude
Published: July 2015

The chemical stability of lanthanide nickelates Ln2NiO4+δ
(Ln = La or Pr) is studied in the temperature range 25 - 1400 °C, both in air and at low pO2 (down to 10-4 atm). Thermal gravimetry analysis (TGA) measurements coupled with thermal in situ X-ray diffraction (XRD) characterization show that all compounds retain their K2NiF4-type structure in these conditions, while remaining oxygen over-stoichiometric up to 1000 °C. For both nickelates, a structural transition occurs around 400 °C at pO2 = 10-4 atm in association with a variation in Dδ in the range 0.06 to 0.02 for Pr2NiO4+δ and La2NiO4+δ, respectively. Interestingly, their cell volume did not vary upon the variation of the oxygen partial pressure. Therefore, these materials do not exhibit a chemical expansion in these conditions, which is beneficial for a fuel cell application as cathode layers. EIS measurements carried out on Ln2NiO4+δ/Ce0.8Gd0.2O2-δ/8wt.%Y2O3-ZrO2 half cells revealed that the electrode are at least as efficient for the oxygen reduction reaction when sintered at pO2 = 10-4 atm, than when sintered in air. Finally, excellent matching was found between the thermal expansion coefficients of the lanthanide nickelates and SOFC electrolytes such as 8wt.% yttria stabilized zirconia (8YSZ) or Ce0.8Gd0.2O2-δ
(GDC), up to 1200 °C either in air or at pO2 = 10-4 atm, which is particularly important to avoid delamination of the half cell layers during solid oxide fuel cell long-term experiments.
Influence of La/Pr Ratio on the Ageing Properties of La2-X
Pr
x
NiO4+δ as Cathodes in IT-SOFCs
Authors: Vibhu Vaibhav , Bassat Jean-Marc , Flura Aurélien , Nicollet Clément , Grenier Jean-Claude , Rougier Aline
Published: July 2015

The present study is focused on alternative oxygen electrodes for IT-SOFCs using Metal Supported Cells (MSCs) conditions. Ln2NiO4+δ (Ln = La, Pr) compounds with the K2NiF4-type structure act as cathode materials for IT-SOFC due to their MIEC properties. Pr2NiO4+δ (PNO) shows excellent electrochemical properties at intermediate temperature while La2NiO4+δ (LNO) exhibits higher chemical stability. Thus, the properties of La2
-x
Pr
x
NiO4+δ (LPNO) mixed nickelates were investigated with the aim to find the best compromise between chemical stability and electrochemical performances. Herein, the chemical stability of the nickelates under air at operating temperatures as well as the evolution of the polarization resistances, R
p, during ageing (i
dc = 0 and i
dc ≠ 0 conditions) were studied for duration up to one month. At i
dc = 0 condition, the ageing of the half cells shows no change in R
p. A different behavior is observed under i
dc ≠ 0 conditions with an increase in R
p in SOFC mode while interestingly, R
p remains stable in SOEC mode.
Lanthanum Nickelate Infiltration into Porous Gd-Doped Ceria As Cathode for Solid Oxide Fuel Cells
Authors: Nicollet Clément , Flura Aurélien , Vibhu Vaibhav , Rougier Aline , Bassat Jean-Marc , Grenier Jean-Claude
Published: July 2015

The lanthanum nickelate La2NiO4+
δ (LNO) has excellent surface exchange reaction rate and oxygen diffusion coefficient. However, when the electrode is shaped by classical screen printing technique, it shows higher polarization resistance (Rp
≈ 1 Ω·cm²) than the standard lanthanum cobaltite-based materials (Rp
≈ 0.1 Ω·cm² for La0.6Sr0.4Co0.2Fe0.8O3-δ). In this study, cathodes are prepared by infiltration of lanthanum nickelate into Gd (20%)-doped ceria (GDC) or Yttria (8%) stabilized zirconia (8YSZ) backbones sintered on different electrolytes. The optimization of the preparation parameters leads to a large decrease of the polarization resistance, down to 0.15 Ω·cm² at 600 °C. A comparison of the results obtained with different electrolytes and backbones allows emphasizing the importance of the interface between the cathode and the electrolyte, as well as the influence of the backbone nature on the value of the polarization resistance. Single cells made with such electrodes on Ni-8YSZ/YSZ half-cells produce 1.44 W·cm-2 at 800°C.
Elastoplastic Properties of (Pr, Ce)O2-δ
Thin Films
Authors: Swallow Jessica G. , Kim Jae Jin , Bishop Sean R. , Smith James F. , Tuller Harry L. , Van Vliet Krystyn J.
Published: July 2015

Electrode materials exhibiting desired ion transport and reactivity properties for energy conversion devices such as solid oxide fuel cells generally also exhibit significant coupling between electrochemistry and mechanics. Properties and responses of thin films representing active electrode dimensions may differ significantly from bulk counterparts due to increased grain boundary densities, space charge effects, or strain. Here, we quantify elastic and plastic properties for the model SOFC cathode material Pr
x
Ce1-x
O2-δ
via nanoindentation. We consider statistical analysis in detail, to quantify uncertainty associated with this method. We confirm no statistically significant difference in Young’s elastic modulus E as a function of Pr dopant concentration at room temperature, or in E of films compared to bulk. In contrast, hardness of thin films exceeds that reported for bulk counterparts at room temperature.
Micro-Modelling of IT-SOFC Electrodes Manufactured through Electrospinning
Authors: Enrico Anna , Aliakbarian Bahar , Perego Patrizia , Costamagna Paola
Published: July 2015

Infiltrated electrodes for intermediate temperature-solid oxide fuel cells (IT-SOFCs) are currently the subject of intense research. Focusing on electrodes with a fibrous microstructure typically obtained through the electrospinning technique, we analyze the role of infiltrations from a modelling point of view. The model includes the evaluation of i) charge transfer reaction occurring at the dopant particles and, possibly, at the electrode/electrolyte interface; ii) electron and/or oxygen-ion conduction along the fiber, and iii) additional charge conduction along the dopant nano-particles, if percolating occurs throughout the electrode structure. The model is applied to doped anodes and cathodes, considering infiltration loadings below and above the percolation threshold. The model allows to evaluate the overall reciprocal electrode resistance 1/Rp
and the electrochemically active thickness (EAT). Simulation results demonstrate good agreement with literature experimental data.
Stability of Bi2O3-Based Ionic Conductor and Its Application on Composite Cathode
Authors: Tsai Shu-Yi , Fung Kuan-Zong , Ni Chung-Ta , Chang Yu-Fan
Published: July 2015

Recently, solid oxide fuel cells(SOFCs) has been considered as desired devices for generating electricity by electrochemical combination of a fuel with an oxidant. Oxygen ion conductors are usually used as the electolytes for SOFCs. Among several types of oxygen ion conductors such as CeO2, stabilized Bi2O3 and ZrO2, Bi2O3with stabilizers exhibit the highest oxygen ion conductivity. Although Bi2O3 tends to be reduced to Bi metal, Bi2O3 incorporated with proper dopants will show enhanced stability against hydrogen. The highest OCV for SOFC using Bi2O3-based electrolyte is around 0.5V which is still too low to be practical. On the other hand, Bi2O3-based system may make a good ionic component for a composite cathode. In this study, we choose yttria-stabilized bismuth oxides (YSB) as ionic conductor and mixed with strontium-doped lanthanum manganite (LSM) for composite cathode. Size effect of LSM on the polarization resistance was investigated by using convertional solid-state reacted and nano-sized LSM. The electrochemical performances of composite cathodes with different LSM:YSB ratio have been investigated at temperature ranging from 500℃to 650℃ using AC impedance spectroscopy. The polarization resistance measured from a symmetric cell consisting of nano-sized LSM-YSB electrodes on a YSB electrolyte is 50% lower than that of submicron-sized LSM-YSB cathodes by SSR (0.21 ohmcm2) at 650℃. The polarization of cathode is reduced because of the mixing of high surface area electric conducting materials and ionic conducting materials. The nanostructure of composite cathode is able to extend triple phase boundary(electronic conductor, ionic conductor,and oxygen gas) and provide numerous reaction sites for electrochemical reaction to occur.
Preparation and Characterization of Pr0.6Sr0.4CoO3-δ
Cathodes in IT-SOFC
Authors: Kanarbik Rait , Kivi Indrek , Tiirats Taavi , Möller Priit , Lust Enn
Published: July 2015

The Pr0.6Sr0.4CoO3-δ (PSC) and La0.6Sr0.4CoO3-δ (LSC) SOFC cathodes were prepared and deposited onto Ce0.9Gd0.1O2-δ | Zr0.85Y0.15O2-δ | Ni-Zr0.85Y0.15O2-δ anode supported half-cells for cyclic voltammetry, electrochemical impedance and chronoammetry analysis. The electrochemical analysis has been conducted under various working temperatures from 550 °C to 800°C and under various fuel and oxidant compositions. The performances of PSC and LSC based single cells at 800 °C were comparatively high with maximum power output 1.48 W/cm2 and 1.28 W/cm2, respectively. It was established that the power output under the same conditions for PSC based SOFC single cell showed slightly higher values comparing to LSC based cells. Short term stability tests show that the both materials have good stability at 700 °C and at cell potential 0.8V and power output 540mW/cm2.
Solid Oxide Fuel Cells Using Novel Cathodes in the BaO-Co2O3-Fe2O3 Composited withGDC10
Authors: Hing Peter , Sukleung Montri , Voo Nyuk Yoong , Lim L C , Atkinson Alan
Published: July 2015

Most cathodes for SOFCs such as LSM, LSC, LSCF contain lanthanum oxide. In this study, cathode materials free from lanthanum oxide have been prepared. Compositions in the BaO-Y2O3-Fe2O3 and BaO-Y2O3-Co2O3-Fe2O3 have been obtained. Selected compositions with high electrical conductivities up to 60Scm-1 have been composited with GDC10 to form composite cathode with matching thermal expansion to GDC10. Symmetrical cells with GDC10 between the experimental cathodes, and small SOFCs with GDC10 as electrolyte, GDC10.NiO as anode and composite cathode have been constructed and evaluated up to 800oC. The electrical conductivity, thermal expansion, impedance and power densities have been studied. Power densities between 400-800oC have been obtained. The results are discussed in relation to the processing, microstructures, properties and performance of the solid oxide fuel cells.
Fabrication of SmBa0.5Sr0.5Co2O5+δ
Cathode Material and Its Application for Sr- and Mg-Doped LaGaO3 Electrolyte-Supported Solid Oxide Fuel Cell
Authors: Lin Tai-Nan , Lee Ruey-Yi , Kuo Jen-Yuan , Ishihara Tatsumi , Hosoi Kohei
Published: July 2015

The layered samarium and strontium doped perovskite oxide SmBa0.5Sr0.5Co2O5+δ (SBSC) was synthesized by glycine nitrate combustion process (GNC). The structure, microstructure, conductivity, coefficient of thermal expansion properties were investigated. The crystallinity of SBSC powder showed pure perovskite phase above 1000 °C according to the XRD and TGA results. With the calcination temperature increased, the crystallinity improved and the powders grew larger and agglomeration occurred. The conductivity of SBSC powders increased with elevated temperature while the coefficient of thermal expansion was 22.6 × 10-6 K-1. SBSC powders were utilized as cathode materials in Sr- and Mg-doped LaGaO3 (LSGM)-based electrolyte-supported solid oxide fuel cell for power performance test. The cell with structure of (NiFe + CMF) | LSGM | SBSC was operated from 700 to 800 °C with humidified H2 as a fuel and ambient air as oxidant. The maximum power densities are 550 and 170 mW cm-2
at 800 and 700 °C, respectively. The experimental results indicate that SBSC is a promising cathode material for intermediate temperature solid oxide fuel cell (IT-SOFC).
Characterisation and Electrochemical Properties of Ce0.8Sr0.2Fe0.9Ir0.04Co0.06 (CSFIC) Cathode Material for Application in Low Temperature SOFC
Authors: Njoku Chima , Omondi B O , Ndungu Patrick
Published: July 2015

In this study, the cathode CSFIC perovskite material has been prepared by sol-gel technique and then tested for its characteristic application in solid oxide fuel cell. The crystal structure was tested using X-ray diffraction and the textural properties were tested using Raman spectroscopy and Fourier transform infrared spectroscopy. The morphology and microstructure was examined using scanning electron microscopy and high resolution transmission electron microscopy. The power density, current density and the DC polarization resistance were measured with a Nuvant TM potentiostat and galvanostat from Fiaxell SOFC technologies connected to the cell setup. These properties were tested for its potential application in low temperature solid oxide fuel cells from 300 to 500 °C. It exhibited a current density of 801.90 mA/cm2, a power density of 471.59 mW/cm2 and an area specific resistance (ASR) of 0.349 Ω/cm2.
Material Characteristics and Electrochemical Performance of YxBa2-XCo2O5+δ Cathode for Solid Oxide Fuel Cell
Authors: Hung I-Ming , Wang Jeng-An , Kuo Jen-Yuan , Lin Tai-Nan
Published: July 2015

A new Y0.8Ba1.2Co2O5+δ cathode was successfully prepared by solid-state reaction method. The structure, microstructure, conductivity, coefficient of thermal expansion and electrochemical properties of the Y0.8Ba1.2Co2O5+δ cathode was conducted by XRD, SEM, 4 DC four-terminal method, thermal gravity analysis and thermomechanical analysis, respectively. The double perovskite structure Y0.8Ba1.2Co2O5+δ with YBa2Co3O9-δ second phase was observed in XRD pattern. The conductivity of Y0.8Ba1.2Co2O5+δ sample increased as temperature increased with a p-type conductor characterization. The Y0.8Ba1.2Co2O5+δ had a maximum conductivity of 240 S/cm at 350 oC. The coefficient of thermal expansion is 19.1 x 10-6, which is close to that of Samaria-doped Ceria (SDC) electrolyte. The Y0.8Ba1.2Co2O5+δ did not react with SDC electrolyte below 950 oC. The Y0.8Ba1.2Co2O5+δ is a potential cathode material for intermediate temperature solid oxide fuel cell.
Metal-supported Solid Oxide Fuel Cell with La0.4Sr0.6Co0.2Fe0.7Nb0.1O3-δ Cathode
Authors: Zhu Tenglong , Han Minfang , Yang Zhibin
Published: July 2015

In this paper, we reported a new method for metal-supported SOFC single cell preparation. Single cell with NiO and Fe2O3 (Ni:Fe=1:1) anode support, Gd0.1Ce0.9O1.95 (GDC) electrolyte and La0.4Sr0.6Co0.2Fe0.7Nb0.1O3-δ (LSCFN) cathode was fabricated through traditional tape-casting, drop-coating, co-sintering and screen-printing. Then the as-prepared single cell was reduced at 700 oC for 1h under 5%H2-95%N2 to get the support reduced. Results show that after annealing the whole cell at 700 oC in the reducing atmosphere, the oxide support was mostly reduced into metal, while the LSCFN cathode maintained its perovskite structure. Electrical impedance spectroscopy tests were carried out with symmetrical LSCFN electrodes reduced at 500-700 oC. Results showed that the polarization resistance lowered down with the reduction temperature increased, which may possibly due to the more oxygen vacancies created at higher reduction temperature.
Electrochemical Characterization of Ag-Y0.5Bi1.5O3 Composite Cathode on 8YSZ-Ce0.78Gd0.2Sr0.02O2-δ Electrolyte Using AC Impedance Spectroscopy
Authors: Hua Ching-Han , Chou Chen-Chia
Published: July 2015

The electrochemical performance of Ag–Y0.5Bi1.5O3 cathodes on a Y0.16Zr0.84O1.92 (8YSZ)–coated Ce0.78Gd0.2Sr0.02O2–δ (GDCS) electrolyte was estimated using electrochemical impedance spectroscopy. The microstructures of the porous composite cathodes and sandwich electrolytes with fluorite structures were investigated using scanning electron microscopy and transmission electron microscopy. Silver in the cathode reduced the surface resistance which improved the current collection efficiency of the electrode. The mixtures consisting of 50 vol%–70 vol% Ag exhibited much lower overpotentials and higher exchange current densities than (La, Sr)(Co, Fe)O3–δ (LSCF) perovskite cathodes below 650 °C. The area specific resistance of the Ag–40 vol% Y0.5Bi1.5O3 cathode decreased to 0.14 Ω cm2 at 650 °C. Favorable oxygen reduction reaction properties and lower activation energies were observed when the cell was operated at temperatures above 600 °C.
Development of La0.6Sr0.4TiXFe1-XO3-Based Composite Cathode Materials for Solid Oxide Fuel Cells
Authors: Iwai Hiroyuki , Suzuki Shinsuke , Inaoka Koji , Murakami Ayumi , Takahashi Yosuke
Published: July 2015

A new cathode material for SOFCs was developed at the R&D Center of Noritake Co., Ltd. It contains La0.6Sr0.4Ti
x
Fe1−x
O3−δ
(0 ≤ x ≤ 0.4) (LSTF) and La0.6Sr0.4CoyFe1−y
O3−δ
(0 ≤ y ≤ 1) (LSCF). Herein, we report the results of our performance evaluation of this cathode material. The optimum composition for the composite cathode material was determined to be LSCF 70 wt%–LSTF 30 wt%. Cathodes with this optimum composition exhibited neither fractures nor delamination from the electrolyte during thermal cycling. The developed cathode material also exhibited high power density and extremely high stability toward hydrogen and ammonia fuels.
Pr2NiO4+δ Cathode Properties and Reaction at Interface with Ceria and Zirconia
Authors: Chiba Reiichi , Ishii Hiroto
Published: July 2015

We fabricated single cells with Pr2NiO4+δ or La2NiO4+δ cathodes and investigated the cathode properties and the influence of a ceria buffer layer using the AC impedance method. The cathodes exhibited very low interface resistance before and after DC current loading. An SDC buffer layer inserted between the cathode and the 8YSZ electrolyte did not improve the cathode interface resistance; it rather degraded the cathode properties. We investigated the phase compatibility of the cathodes with ceria (GDC) or zirconia (8YSZ) by x-ray diffraction analysis. We revealed that ceria is highly reactive with Pr2NiO4+δ or La2NiO4+δ, but they are not reactive with 8YSZ electrolyte under the cathode sintering conditions.
Enhancing Performance of Stabilized Bismuth Oxide-Based Cathodes via Infiltration Process for LT-SOFCs
Authors: Park Jin Wan , Yun Byeong Hyeon , Joh Dong Woo , Lee Kang Taek
Published: July 2015

Nanostructured La0.8Sr0.2MnO3-δ (LSM) - Er0.4Bi1.6O3 (ESB) composite cathodes for lower temperature solid oxide fuel cells (LT-SOFCs) were developed via infiltration process. The perovskite phase of LSM nanoparticles deposited on the porous ESB scaffold was confirmed by X-ray diffraction (XRD). The microstructural evolution of the established nanostructures was observed using scanning electron microscope (SEM). The cathodic polarization resistances of the developed cathodes on GDC were measured by electrochemical impedance spectroscopy (EIS) and compared to the conventional LSM-ESB composite cathodes. The resultant area specific resistance (ASR) of the LSM infiltrated ESB cathodes was 1.24 Ω-cm2 at 600 °C, which is ~34% lower than that of the conventional LSM-ESB composite cathode (1.88 Ω-cm2) primarily due to enhanced ORR activities with increased TPB density in the nanostructured cathodes.
PrBaCo2O6-δ
- Ce0.8Sm0.2O1.9 Composite Cathodes for Intermediate Temperature Solid Oxide Fuel Cells
Authors: Tsvetkov Dmitry S. , Tsvetkova Nadezhda S. , Ivanov Ivan L. , Malyshkin Dmitry , Sereda Vladimir V. , Zuev Andrey Yu.
Published: July 2015

The single phase oxide PrBaCo2O6-δ and composites (100-y) PrBaCo2O6-δ - y Ce0.8Sm0.2O1.9 (y = 10 - 30 wt.%) were investigated as cathode materials for intermediate temperature solid oxide fuel cells. The chemical compatibility, thermal expansion, DC conductivity and electrochemical performance of these materials were studied. As a result, exchange by Pr and Sm was found between PrBaCo2O6-δ and Ce0.8Sm0.2O1.9. Cation exchange was found for both oxides not to lead to change of the crystal structure and results in slightly decreasing a and c cell parameters for Ce0.8Sm0.2O1.9 and PrBaCo2O6-δ, respectively. This exchange was shown to affect significantly both thermal expansion and total conductivity of the composites studied. As a consequence, thermal expansion coefficient of the composite cathodes exceeds significantly that of the electrolyte.
Crystal Structure and Characterization of La1-xBixMnO3+δ
Authors: Kaimieva Olga , Morozova Maria , Buyanova Elena , Mikhaylovskaya Zoya , Petrova Sofia , Tarakina Nadezda
Published: July 2015

The La1-x
Bi
x
MnO3+δ (x=0.0-0.5) solid solutions were synthesized using three different methods: solid-state synthesis, citrate-nitrate combustion synthesis. All compositions crystallize in a rhombohedral perovskite structure, independent of the synthesis method. Two ranges with linear temperature dependence of the unit cell parameters have been observed during in-situ heating X-ray powder diffraction experiments. The transition between the two ranges occurs at 730°C and is explained by chemical expansion at high temperatures. The chemical compatibility between the obtained solid solutions and bismuth-containing electrolytes (Bi4V1.7Fe0.3O11, Bi13Mo5O34 and Bi3Nb0.8W0.2O7.1) was studied. Interaction between these materials has been observed at temperatures higher than 600°С.
Rate Determining Step in ORR of PrO
x
-Based Film Cathodes
Authors: Okada Satoshi , Miyoshi Shogo , Yamaguchi Shu
Published: July 2015

Although it is commonly well known that the oxygen reduction reaction (ORR) at cathodes surface limits an overall SOFC performance, important issue of understanding ORR mechanism, necessary for further improvement of SOFC performance, is still in debate to date. One of the important factor of ORR that has been missing, is the chemical potential of electrons, me’, in oxide cathodes, which is related to the basicity of cathodes as well as RedOx state. In this report, cathode performance of PrO
x
-based materials has been examined to understand the effect of me’ and modification by applying basic component of BaPrO3 using EIS. For all of the examined PrO
x
-based electrodes, the area-specific conductivity corresponding to the ORR activity shows Po2 exponent of 1/2 under an isothermal condition, which suggests the elementary reaction of peroxide ion and oxygen vacancy is the rate-determining step. Improvement of the ORR activity was achieved by surface modification with BaPrO3, which is ascribed to the upward shift of E
F and resultant increase in the population of surface peroxide ion.