bluuebunny/crossref_metadata_2025 huggingface dataset:
Performance Improvement of Oxide Catalyst-doped Anode Supported SOFCs for Methane Fuel
Authors: Myung Jae-ha , Lee Jong Jin , Hyun Sang-Hoon
Published: September 2009

Solid oxide fuel cells (SOFCs) with a conventional Ni cermet anode suffer carbon deposition when directly used with hydrocarbon fuels. In this work, oxide catalysts containing Li2TiO3, which can prevent carbon deposition, were developed and the performance of catalyst-doped anode-supported SOFCs for use with CH4 fuel was evaluated. Li2TiO3 catalyst synthesized at 700oC for 24 h by a solid state reaction method showed excellent resistance to carbon deposition on Li2TiO3 catalyst-doped Ni-YSZ anodes. Our SOFC unit cells were manufactured by laminating catalyst-doped Ni-YSZ anodes and YSZ electrolytes prepared via tape-casting followed by co-sintering the laminate at 1325oC, screen-printing the LSM-YSZ cathode on the YSZ electrolyte, and sintering at 1150oC. The power density of the catalyst-doped Ni-YSZ anode-supported unit cells was higher than 0.4 W/cm2 at 800oC and, in particular, their long-term stability improved considerably when used with CH4 fuel.
Effects of Impurities Contained in Coal-Derived Syngas on the Performance of SOFCs
Authors: Kuramoto Koji , Matsuoka Koichi , Suzuki Yoshizo , Kishimoto Haruo , Yamaji Katsuhiko , Xiong YuePing , Horita Teruhisa , Brito Manuel , Yokokawa Harumi
Published: September 2009

Power generation tests using a single-cell SOFC fueled by coal-derived syngas were conducted under a constant voltage of -0.8 V versus air (reference). The syngas was produced in the steam gasification of pulverized coal in a laboratory-scale fluidized-bed gasifier and was supplied to SOFC anode with different gas cleaning conditions: with/without filtrations and water washing. It was possible to generate the electrical current by the coal-derived syngas for several hours and we found that the degradation behavior of SOFC anode was notably affected by gas cleaning conditions. A SEM-EDX analysis confirmed that the micro-scale change in morphology of SOFC anode occurred due to the sintering of Ni particles over the anode layer, suggesting that eutectic melting of Ni might be enhanced by some impurities contained in the coal derived syngas.
Performance of a New Cu-Ceria Based Anode for SOFCs Running on Different Fuels
Authors: Fuerte Araceli , Valenzuela Rita Ximena , Escudero María J. , Daza Loreto
Published: September 2009

A new Cu-ceria based material was evaluated as the anode for SOFC. Physicochemical characterisation, electrical properties in reducing atmosphere as well as thermal and chemical compatibility with common SOFC electrolytes were first investigated. A single cell with 8YSZ electrolyte and this anode material was prepared and tested in H2 and methane fuels at 1023 K, using air as oxidant. Cell was running for more than 340 h and demonstrated the ability of utilise not only hydrogen but also methane as fuel. The results suggest that material under study can be considering as anode for SOFC operating with hydrogen or hydrocarbons. Cell performance could be improved by optimising the cell fabrication method as well as using an appropriate electrolyte and cathode material to operate at this relative low temperature, such us doped ceria and perovskites respectively.
Development of Multilayer Anodes for Proton-conducting Solid Oxide Fuel Cells
Authors: Taillades Mélanie , Batocchi Pierre , Essoumhi Abdel , Taillades Gilles , Jones Deborah J. , Rozière Jacques
Published: September 2009

Advanced cermet electrodes of Ni-BaCeO.9Y0.1O2.95, suitable for Intermediate Temperature PCFC, have been elaborated using gelling starch as pore forming agent. SEM and mercury porosimetry measurements show a strong dependence of the microstructure upon the starch content. As the starch content increase, a gradual creation of percolating starch network is clearly shown. An half cell showing a gradient of porosity and a thin electrolyte dense layer was successfully obtained by a simple co-pressing and co-sintering process. The polarization ASR (0.13 Ohm.cm2) is obtained for the cell architecture investigated in this work
Investigation of Sr-doped and Sr-free LaMn1-yCryO3{plus minus}δ Perovskites as Sulfur Tolerant SOFC Anodes
Authors: Deleebeeck Lisa , Birss Viola
Published: September 2009

Sr-doped and Sr-free La1-xSrxMn1-yCryO3{plus minus}δ (LSMC) perovskite-type oxides were synthesized and tested for use as intermediate temperature anodes for SOFC applications. Thermo-chemical and chemical stabilities were tested in hydrogen and low ppm H2S: H2 at 800åC. Relative reducibility was determined by temperature program reduction using thermo-gravimetric analysis. This was correlated with oxygen non-stoichiometry determined by permanganate titration. The final phase after reduction at 1100åC was determined by powder X-ray diffraction and the ability of these materials to recover after reduction was tested by re-sintering in air. Electrochemical testing revealed catalytic activity towards hydrogen as a function of changing sintering temperature and operating temperature, as well as Sr and Cr content LSMC materials were found to be chemical stable in upto 10 ppm H2S in humidified hydrogen at 800åC, and Sr-free LMC materials were shown to have reasonable catalytic activity towards the hydrogen oxidation reaction at 700 and 800åC.
Impedance Identification of Lanthanum Strontium Vanadate Anode in H2-H2O-He Atmosphere
Authors: Ge Xiaoming , Chan Siew Hwa
Published: September 2009

Impedance behavior of composite anode of strontium doped lanthanum vanadate and yttria-stabilized zirconia was investigated in H2-H2O-He atmosphere. It included reaction impedance, gas concentration impedance, and inductive loops that only emerged at high biased conditions. The gas concentration impedance was inhibited significantly in wet atmosphere. A detrimental water effect was observed for up to 15 vol % H2O.
Synthesis and Characterization of LnBaCo2O5+δ Layered Perovskites as Cathodes for Intermediate-Temperature Solid Oxide Fuel Cells
Authors: Wang Wei , Peh Teng Sheng , Chan Siew Hwa , Zhang Tian Shu
Published: September 2009

LnBaCo2O5+δ (Ln=Pr, Gd, Sm, Nd) layered perovskites were successfully synthesized by an EDTA-citrate complexing method. Cathode performance of LnBaCo2O5+δwas investigated in the intermediate temperature range of 450oC-750oC on Sm-doped CeO2 (SDC) electrolyte. PrBaCo2O5+δ (PBCO) showed reasonably good performance among all the compounds examined. Addition of SDC phase to form PBCO/SDC composite cathode greatly improve the electrode performance. The lowest polarization resistance of 0.15-0.17 Ωcm2 at 600oC was achieved on PBCO/SDC composites with PBCO content of 60-70wt%. The results demonstrate the potential of layered perovskites as alternative SOFC cathodes for the intermediate temperature operation.
Activation of LSM-based SOFC Cathodes - Dependence of Mechanism on Polarization Time
Authors: Haider M. Ali , Vance Andrew A , McIntosh Steven
Published: September 2009

La0.8Sr0.2MnO3-δ (LSM) film electrodes of thickness 100-700 nm were deposited onto yttria-stabilized zirconia (YSZ) and cerium gadolinium oxide (CGO) electrolyte pellets by ultrasonic spray pyrolysis. The activation behavior upon initial application of cathodic polarization was studied with respect to the magnitude of applied potential and current, duration of applied potential, and surface doping with Sr, La and Mn oxides or La0.6Sr0.4FeO3 (LSF) nanoparticles. We provide evidence for two separate activation phenomena - a surface dominated process during short-term application, and bulk pore formation during long-term application of cathodic current.
Plasma Sprayed LSM Cathode for Solid Oxide Fuel Cells
Authors: Wittmann-Ténèze Karine , Sauvet Anne-Laure
Published: September 2009

Lanthanum Strontium Manganate (LSM) and LSM/Yttria Stabilized Zirconia (YSZ) cathode materials were developed by Vacuum Plasma Spraying (VPS) and Air Plasma Spraying (APS). A parametric study on thermal spraying conditions was performed to manufacture LSM and LSM/YSZ coatings having a good cohesion, high enough porosity and a minimal decomposition of the LSM phase. Layers open porosity was measured by the Archimedes method and phase analysis was done by X-Ray Diffraction (XRD). Electrochemical characterization was performed by impedance spectroscopy at 900{degree sign}C under air on selected cathode materials. Different electrochemical performances were obtained following the spraying atmosphere and the cathode composition. The most efficient cathode developed in this work is composed of two layers: LSM/YSZ as active layer and LSM as collecting layer obtained by APS.
Reducing the Cathode Losses by Optimization of IT-SOFC Cathode Microstructure
Authors: Ma Libin , Wang Haiqian , Xie Bin
Published: September 2009

In order to reduce the cathode losses, some studies were carried out on optimizing the LSM-based cathode microstructure. Firstly, the current collecting coatings were prepared with LSM sintered at different temperatures. The sample sintered at 1150 {degree sign}C exhibited the best performance in terms of microstructure and the electrical conductivity. Secondly, composite cathode materials with different LSM contents were prepared. When LSM three-dimensional network was formed, the conduction of the composite cathode was dominated by LSM phase, resulted in higher conductivity and lower activation energy. When the YSZ network formed, the composite exhibited a lower polarization resistance. Electrochemical Impedance Spectroscopy implied that at the temperature of 750 {degree sign}C the composite cathode with 50 wt.% LSM displayed the lowest Rp value of 0.26 Ω cm2.
High Temperature Defect Equilibrium, Solid State Properties and Crystal Structure of La0.6Sr0.4Co1-yFeyO3-δ (y=0.2, 0.4, 0.6, 0.8) for Cathode of Solid Oxide Fuel Cells
Authors: Fukuda Yasuhiro , Hashimoto Shin-ichi , Sato Kazuhisa , Yashiro Keiji , Mizusaki Junichiro
Published: September 2009

Oxygen nonstoichiometry of La0.6Sr0.4Co1-yFeyO3-δ (y=0.2, 0.8) were measured by high temperature gravimetry and coulometric titration as a function of temperature and oxygen partial pressure. The lattice constant is also observed by HT-XRD as a function of temperature and oxygen partial pressure. The relationship between lattice constant and oxygen deficiency is determined from these results. Almost linear behavior was obtained between them.
Long-Term Study of MIEC Cathodes for Intermediate Temperature Solid Oxide Fuel Cells
Authors: Endler Cornelia , Leonide André , Weber André , Tietz Frank , Ivers-Tiffée Ellen
Published: September 2009

The time-related change of anode supported single cell performance for intermediate temperature SOFC was evaluated continuously up to 700 hours of operation. For the first time, cathodic and anodic polarization losses were separated by high resolution impedance studies based on DRT analysis (distribution of relaxation times) followed by a CNLS fitting approach. The cathodic polarization resistance (15mΩcm2 at t = 11 h), by far the smallest part, could only be visualized in the relevant frequency range by well selected and adapted experimental parameters. Within 700h the cathode resistance increases by 400% (63mΩcm2 at t = 700 h) undergoing a nonlinear degradation rate which can not explained by microstructural changes but probably by compositional changes.
Inhibition of the Electrode Particle Growth in the SOFC
Authors: Murata Kosuke , Hirano Atsushi , Imanishi Nobuyuki , Takeda Yasuo
Published: September 2009

The La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) surface modified with Ag fine particles exhibits enhancement of the electrode properties, but the grain growth of Ag particles over long term operation results in deterioration of the cell performance. In order to suppress the growth of Ag particles in LSCF, Ce0.8Gd0.2O1.9(GDC) fine particles were distributed over the porous LSCF-Ag composite electrode using the infiltration technique with a solution of Ce0.8Gd0.2(NO3)x in citric acid. In the accelerated test at high temperature, the addition of GDC was revealed to be effective for the prevention of Ag particle grain growth, and no increase in the electrode resistance, which corresponds to a decrease in oxygen reduction, was observed.
Performance of (Ln0.5M0.5)FeO3-δ Perovskites as Cathode for SOFCs.: Effect of Mean Radious of the A site Cations
Authors: Vidal Karmele , Rodriguez-Martinez Lide M. , Ortega-San-Martín Luis , Martínez-Amesti A. , No M.Luisa , Rojo Teófilo , Laresgoiti Ander , Arriortua María Isabel
Published: September 2009

Crystal structure, microstructure, electrical conductivity and electrochemical performance of a new family of iron perovskites with the general formula Ln0.5M0.5FeO3-δ (Ln = La and/or Pr; M = Sr, Ca or/and Ba) has been studied as function of mean A cation radius . All the samples have a rhombohedral structure (space group: R-3c). SEM images show that the average grain size decreases with increasing . The DC four-probe measurements indicate that all samples have high electrical conductivity, increasing with . The electrochemical behaviour of these cathode materials was evaluated by using I-V curve measurements and AC impedance spectroscopy over three electrodes electrolyte supported cells. The results show a great improvement in cathode performance and a significant decrease in polarization resistance with increasing mean A cation radius .
Effect of Infiltrate Solution Additives on Samarium Strontium Cobaltite-Cerium Gadolinium Oxide Nano-Composite SOFC Cathodes
Authors: Nicholas Jason D. , Barnett Scott A.
Published: September 2009

Nano-composite SSC (Sm0.5Sr0.5CoO3-x) - GDC (Ce0.9Gd0.1O1.95) Solid Oxide Fuel Cell cathodes were produced by infiltrating SSC nitrate solutions with/without additives into GDC scaffolds. X-ray diffraction indicated that fired precursor solutions containing the surfactant Triton X-100 had less secondary phases than similarly processed pure nitrate solutions. Further, precursor solutions containing citric acid, a chelating agent, produced nearly phase-pure SSC after 1 hour at 800{degree sign}C. These solution additives did not have a large effect on the cathode polarization resistance. In contrast, alterations of the infiltration procedure influenced the SSC nano-particle size and hence the polarization resistance. Polarization resistances of 0.1 Wcm2 at 600{degree sign}C were achieved with a single infiltration of concentrated solution. Polarization resistance predictions made using microstructural observations and a modified Tanner, Fung, Virkar model were found to be within 40% (without fitting parameters) of the experimentally measured values, regardless of the testing temperature, cathode thickness, solution additives, and cathode synthesis conditions.
Improving Stochiometery and Processing of LSCF Oxygen Electrode for SOFC
Authors: Ansar Asif , Soysal Dennis , Ilhan Zeynep , Wagner Nobert , Wolf Steffen , Ruckdäschel Robert
Published: September 2009

La1-xSrxCo0.2Fe0.8O3-δ deposits were developed for oxygen electrode for SOFC using powders of different stochiometery. The manufacturing of functional layer was carried our by atmospheric plasma spraying (APS) using TriplexPro gun. The processing was improved to obtain microstructure exhibiting high gas permeability and no degradation of the powders while attaining high production rates. Dwell time of the particles in the plasma was the established as the critical factor for the degradation and permeability. The improved functional coatings had a porosity of about 20 vol%. The CTE in air flow at 800{degree sign}C was, however, 15.6 x10-6 K-1. Electrochemical tests on SOFC cells having cathodes of different stochiometery with improved processing were conducted. These cells were produced using metal supported design, had YSZ as electrolyte and NiO+YSZ as anode. No interlayer (such as CGO) between YSZ and LSCF cathode was introduced. At 800{degree sign}C, power densities of above 640 mW/cm² at 0.7 V were recorded with H2/air for cell having La0.60Sr0.40Co0.2Fe0.8O3-δ as cathode. Cells consisting of La0.58Sr0.4Co0.2Fe0.8O3-δ and La0.78Sr0.2Co0.2Fe0.8O3-δ had 479 and 496 mW/cm² under similar conditions. Using equivalent circuit diagrams the contribution of different polarizations on the cell performance were separated and cathodes were compared. La0.60Sr0.40Co0.2Fe0.8O3-δ was found to have best electrochemical performance followed by La0.58Sr0.40Co0.2Fe0.8O3-δ and La0.78Sr0.20Co0.2Fe0.8O3-δ.
Fabrication of Composite LSCF-SDC Cathode Coatings by Plasma Spray Processing
Authors: Harris Jeffrey , Kesler Olivera
Published: September 2009

Composite cathode coatings were fabricated by plasma spraying mixtures of La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) and Ce0.8Sm0.2O2-δ (SDC) powders. These electrodes were fabricated using plasmas with low powers. X-ray diffraction (XRD) and energy dispersive x-ray spectroscopy (EDX) were performed to determine how the relative deposition efficiency of the materials is influenced by the process parameters and the relative particle sizes of the feedstock powders. The microstructures of the electrodes were evaluated by scanning electron microscopy. Although pure SDC adhered poorly onto substrates, the SDC phase could be incorporated into a composite coating using low power plasmas.
Performance Study of Alternative (La,Sr)FeO3-δ and (La,Sr)(Co,Fe)O3-δ MIEC Cathode Compositions
Authors: Leonide André , Rüger Bernd , Weber André , Meulenberg Wilhelm A. , Ivers-Tiffée Ellen
Published: September 2009

In this study two cathodes, La0.68Sr0.3FeO3-δ and La0.68Sr0.3Co0.2Fe0.8O3-δ, are characterized by electrochemical impedance spectroscopy. The chemical surface and diffusion coefficients of both cathode materials are obtained directly from impedance measurements performed on full anode supported solid oxide fuel cells (SOFC). This is done by a combined distribution of relaxation times and equivalent circuit impedance analysis method, which allows a high resolved identification and deconvolution of each single polarization mechanisms contributing to the overall loss of the cell.
Oxygen Reduction Kinetics and Transport Properties of (Ba,Sr)(Co,Fe)O3-δ and Related SOFC Cathode Materials
Authors: Wang Lei , Merkle Rotraut , Maier Joachim
Published: September 2009

Oxygen surface reduction kinetics is studied with the help of impedance spectra measured on dense thin film microelectrodes of (Ba1-xSrx)(Co1-yFey)O3-δ (BSCF) and related SOFC cathode materials. Effective oxygen exchange rate constants kq, calculated from area-specific surface resistances Rs extracted from the impedance spectra, increase in the sequence of LSM (La1-xSrxMnO3+/-δ), LSCF (La1-xSrxCo1-yFeyO3-δ) and BSCF. The influence of bulk properties, such as electronic conductivity and Goldschmidt tolerance factor, on kq is investigated to supply information for identifying the rate-determining step. Possible roles of oxygen vacancies in the oxygen surface incorporation reaction are discussed.
Characterization of SmBaCoFeO5+δ Cathode Material for Intermediate-temperature Solid Oxide Fuel Cells
Authors: Lu Shiquan , Meng Xiangwei , Long Guohui , Wang Xiaomin , Ji Yuan
Published: September 2009

Cathode material SmBaCoFeO5+δ (SBCF) was synthesized by a combined EDTA-citrate complexing sol-gel method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), AC impendence spectroscopy, respectively. The results showed that the SBCF cathode had an orthorhombic perovskite-structure and formed a good contact with the Ce0.9Gd0.1O1.95 (GDC) electrolyte after sintering at 950°C for 2h. Based on symmetric cell test, area specific resistance of SBCF on GDC electrolyte was as low as 0.1Ω cm2 at 800°C. The maximum power densities of a cell using the SBCF cathode are 431 mWcm−2, 313mWcm−2 and 200mWcm−2 at 800°C, 750°C and 700°C, respectively. Preliminary results demonstrate that SBCF is a very promising cathode material for application in intermediate-temperature solid oxide fuel cells (IT-SOFCs).
Improved Performance of Ba0.5Sr0.5Zn0.2Fe0.8O3-δ Cathodes for Intermediate-Temperature Solid Oxide Fuel Cells
Authors: Kong Lingping , Lu Zhe , Wei Bo , Huang Xiqiang , Su Ren , Su Wenhui
Published: September 2009

In this study, Ba0.5Sr0.5Zn0.2Fe0.8O3-δ(BSZF) oxide, synthesized by solid-state reaction method, was modified for the cathode of solid oxide fuel cells. Three kinds of BSZF-based cathodes, pure-BSZF, BSZF-GDC (30wt.%Ce0.9Gd0.1O1.95) and BSZF-GDC-Ag, were investigated using AC impedance spectroscopy. The results demonstrated the performance of BSZF-GDC-Ag cathode was greatly improved, for example, at 700°C its polarization resistance decreased by 61% in comparison with pure BSZF.
Performance of Zinc-doped Perovskite-type Cathodes at Intermediate Temperatures and Under Carbon Dioxide Atmosphere
Authors: Martynczuk Julia-Maria , Efimov Konstantin , Robben Lars , Feldhoff Armin
Published: September 2009

Zinc-doped (BaSr)FeO3-δ perovskite-type membranes were found to exhibit an excellent long-term stability at high and intermediate temperatures under an oxygen partial pressure gradient. With carbon dioxide as sweep gas, the oxygen permeation diminishes almost completely. By X-ray diffraction a phase mixture of hexagonal, tetragonal and cubic perovskite with a (Ba0.4{plus minus}0.1Sr0.6{plus minus}0.1)CO3 layer and some zinc oxide was found. Transmission electron microscopy showed that the dense perovskite membrane is decomposed into phases with different morphologies accompanied by pore and crack formation in a surface layer of 5 µm. After switching to helium as the sweep gas, a hexagonal perovskite phase is still present, which reduces the oxygen permeation flux. A short heating to 950 {degree sign}C regenerates the oxygen permeation flux. The appearance of the carbonate structure leads to a breakdown of the oxygen permeation ability, but the effect of the carbon dioxide is totally reversal after a short high temperature treatment.
Electrochemical Performances of Cells Containing Alternative Oxygen Electrodes, Ln2NiO4+δ (Ln=Nd, La)
Authors: Chauveau Florent , Mougin Julie , Mauvy Fabrice , Bassat Jean-Marc , Grenier Jean C.
Published: September 2009

Two rare-earth nickelates, with compositions Nd2NiO4+δ and La2NiO4+δ have been investigated as oxygen electrodes. Their polarization resistance was determined on symmetrical half-cells and was found much lower than for classical Sr-doped LaMnO3 (LSM) perovskite. Then Nd2NiO4+δ was integrated in an electrolyte supported cell and tested in both fuel cell (SOFC) and electrolysis (SOEC) modes. The performances of this cell were higher than the one of a LSM-containing one. ASR values measured for this cell at 0.7 V were equal to 0.60 and 1.09 Ω.cm², at 850 and 750{degree sign}C, respectively. At 850{degree sign}C, this value is 1.7 times lower compared to the LSM-containing cell. At 750{degree sign}C it is 5.6 times lower. These results seem to show that nickelates are particularly suitable for a use below 800{degree sign}C. Similar conclusions were obtained in electrolysis mode.
Investigations of Graded Cathodes to Improve SOFC Electrochemical Performances
Authors: Rieu Mathilde , Sayers Ruth , Laguna-Bercero Miguel A. , Skinner Stephen , Lenormand Pascal , Ansart Florence
Published: September 2009

Mixed ionic and electronic conducting oxides (MIEC) used as cathodes for solid oxide fuel cells (SOFC) have demonstrated their interest to enhance the electrocatalytic activity compared to only electronic oxides. In this paper, MIEC oxides belonging to the Ruddlesden-Popper series, such as La2NiO4, have been prepared by the sol-gel route to synthesize powders and a dip-coating process as the deposition method. In this work, this low cost process was used to prepare various graded cathodes on YSZ pellets and impedance spectroscopy studies were performed to characterize electrochemical performance. By adapting slurries, cathode layers with different porosity and thicknesses were obtained. A ceria gadolinium oxide (CGO) barrier layer has also been introduced. A systematic correlation between microstructure, composition and electrochemical performance of these cathodes has been attempted. Significant enhancement in Area Specific Resistance (ASR) has been achieved through the use of a compact interlayer when compared with standard porous La2NiO4 electrodes.
Oxygen Nonstoichiometry, Crystal Structure, and Mechanical Properties of La2NiO4+δ
Authors: Nakamura Takashi , Takeyama Yohei , Watanabe Satoshi , Yashiro Keiji , Sato Kazuhisa , Hashida Toshiyuki , Mizusaki Junichiro
Published: September 2009

Crystal structure and mechanical properties of La2NiO4+d were measured by high temperature X-ray diffractometry and in-situ small punch test as a function of temperature and oxygen partial pressure. As P(O2) increases, the lattice parameter perpendicular to the perovskite layer increases and that parallel to the layer slightly decreases, and the lattice volume slightly increases. Apparent and true thermal expansion coefficients were calculated from the variation of the lattice constants. The elastic modulus and the fracture strength become larger at higher P(O2) condition. This may be caused by the structural change due to excess oxygen.
Property Study of La2-xSrxNiO4 (x {less than or equal to} 0.8) to be used for IT-SOFCs Cathode
Authors: Inprasit Thitirat , Limthongkul Pimpa , Wongkasemjit Sujitra
Published: September 2009

Materials with Ruddlesden-Popper structure (A2BO4) such as La2NiO4 system have been identified as the new cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs) as their coefficient of thermal expansion values match those of the currently used electrolytes. Moreover, such materials have shown mixed ionic and electronic conductivity desirable for cathodes. The low electronic conductivity of La2NiO4 remains a challenge. To improve this property, investigations on La2-xSrxNiO4+δ (x = 0, 0.4, and 0.8) prepared via sol-gel and solid state reaction processes were carried out in this study. Effects of Sr substitution on A sites on physical and electrical properties of the compound were investigated and compared. A simple preparation sol-gel process, carried out at room temperature and using water as solvent for the synthesis of La2-xSrxNiO4+δ, was successfully developed. The solgel synthesis method yielded more homogenous samples with higher conductivity compared to those synthesized via the solid state reaction method. Conductivity as high as 160 S/cm at 500oC was observed for La1.2Sr0.8NiO4+δ synthesized via the sol-gel process.
Fabrication and Characterisation of Cathode Support-tubes for Micro-tubular SOFC Application
Authors: Luebbe Henning , Rossen John , Diethelm Stefan , Van Herle Jan , Hofmann Heinrich , Bowen Paul , Snijkers Frans , Betz Thomas
Published: September 2009

Tubes of diameter <5mm of a nickelate cathode material of composition Nd1.95NiO4 were prepared by cold-isostatic pressing (CIP) and extrusion. These tubes are intended as cathode support structure for micro-tubular SOFCs at reduced working temperatures around 700{degree sign}C. The characteristics of these tubes - porosity, pore size, geometric dimensions and surface roughness - were measured by various techniques such as mercury intrusion, SEM-Imaging and with an in-house built diffusion setup. Diffusion measurements yielded average pore sizes of 0.12 μm for CIP-ed tubes and 0.22 μm for extruded tubes. Estimation of the loss due to oxygen diffusion has shown that the wall thickness of CIP-ed tubes must be reduced prior to coating processes in order to limit oxygen concentration overpotential loss during operation.
Fabrication and Properties of Perovskite-type Ln0.8Sr0.2Cu0.9Fe0.1O2.5-δ(Ln=La, Pr, Nd, Sm, Gd) Ceramics
Authors: Song Xiwen , Zhong Chongying , Zhou Fen , Hao Xihong , Jia Guixiao , An Shengli
Published: September 2009

In this work, the perovskite oxides Ln0.8Sr0.2Cu0.9Fe0.1O2.5-δ (LSCF, Ln=La, Pr, Nd, Sm, Gd) are successfully synthesized by a pechini-type gel method. The crystal structures and the thermal stabilities of these oxides are characterized using powder X-ray diffraction (XRD) and differential thermal analysis (DTA), respectively. The results indicate that the major perovskite phase is formed after sintering at 800 oC, and the LSCF perovskite is thermodynamically stable and chemically compatible to Sm0.2Ce0.8O1.9 electrolyte below 1000 oC. The result from the electrical conductivity measured by the four-probe D.C. method shows that, as the ionic radius of Ln3+ decreases, the electrical conductivity decreases from 632.7 S cm−1 for La0.8Sr0.2Cu0.9Fe0.1O2.5-δ to a low value of 14.7 S cm−1 for Gd0.8Sr0.2Cu0.9Fe0.1O2.5-δat 700 oC.
Thermal Expansion Properties of Sr1-xLaxTiO3-δ ((0 {less than or equal to} x {less than or equal to} 0.3) Perovskites in Solid Oxide Fuel Cells
Authors: Wang Zhenwei , Mori Masashi , Itoh Takanori
Published: September 2009

Sr1-xLaxTiO3-δ perovskites are strong candidates for use as the anode and interconnect materials in solid oxide fuel cells. The thermal expansion properties of these materials with La contents of 0 <= x <= 0.3 during oxidation-reduction (redox) cycling were investigated. The thermal expansion coefficients (TECs) in air increased with increasing La content. TECs in an H2 atmosphere showed an opposite trend. Shrinkage occurred in the reducing atmosphere, and no further shrinkages of the reduced samples were observed upon re-exposure to the same environment. On the other hand, the pre-reduced samples expanded in air. These thermal expansion properties are expected to be related to the release and absorption of oxygen as well as the disappearance of excess cation and oxygen vacancies in the perovskite structure.
Conductivities and Seebeck Coefficients of donor-doped-SrTiO3 Oxide Ceramics
Authors: Niwa Eiki , Sato Kazuhisa , Yashiro Keiji , Mizusaki Junichiro
Published: September 2009

Strontium titanate, SrTiO3 has a cubic perovskite-type structure in the wide range of the temperature and is chemically stable from oxidizing to reducing atmospheres. Moreover donor-doped-SrTiO3 oxides have high electric conductivity. In this study, the examination was made on the possibilities of the application of polycrystalline of SrTi1-yNbyO3 and Sr1-xYxTiO3 to the interconnector materials of SOFCs. The result of conductivities corresponded to Kroger-Vink diagram of donor-doped-SrTiO3.
Effect of the Synthetic Method on the Structure and Electrical Conductivity of La0.5Ba0.5FeO3 as SOFC Cathode Materials
Authors: Ecija Ana , Vidal Karmele , Larrañaga Aitor , No M.Luisa , Laresgoiti Ander , Arriortua María Isabel
Published: September 2009

The perovskite oxide La0.5Ba0.5FeO3 (with = 1.34 Aå) has been synthesised by ceramic and glycine-nitrate routes. The obtained compounds have been compared as cathode materials for intermediate temperature solid oxide fuel cells (SOFCs). These materials have been studied by inductively coupled plasma atomic emission spectroscopy, X-ray diffraction, scanning electron microscopy, four-probe conductivity measurements and electrochemical impedance spectroscopy. La0.5Ba0.5FeO3 samples prepared by the two methods have a mixture of rhombohedral (R-3c) and cubic (Pm-3m). The SEM images on bulk samples show that their morphology is clearly different depending on the preparation method. The electrical bulk conductivity of the samples has been measured in the 30-900ºC temperature range. The compound obtained by ceramic method show higher electrical conductivity than the one synthesised by glycine-nitrate route. Electrochemical impedance spectroscopy measurements have been realised at 700 and 800ºC. Impedance results indicate better electrochemical performance for the sample obtained by glycine-nitrate process.
Thermal stability of silver-MOx (M = Mn, Fe, Co, Ni) Composite Cathode for IT-SOFCs
Authors: Saka Hideyuki , Hirano Atsushi , Imanishi Nobuyuki , Takeda Yasuo
Published: September 2009

Silver nano composite cathode is expected as one of the new materials for intermediate temperature SOFCs cathode. Characteristics of silver are high conductivity and oxygen ion conductivity so it is a suitable material. Generally the silver were introduced by wet infiltration method. Infiltrating Ag powder into LSCF, the maximum output power was improved. However, the power density decreased with time above 700 ºC, because of the growth of Ag particle. In this study, we have synthesized Ag and transition metal oxides (MOx, M = Mn, Fe, Co, Ni) composite cathode with various mixing ratio using AgNO3 and MNO3 solutions in citric acid. The material of electrode is able to make in a nano composite electrodes by oxide into Ag at intermediate temperature. In the characteristic of electrochemical, power density of Ag-NiO electrode on anode supported cell was increased from 0.098 W/cm2 to 0.612W/cm2 at 700 ºC.
Oxygen Pathway in Ag Cathode using Oxygen Isotope Exchange and Secondary Ion Mass Spectroscopy
Authors: Muranaka Minoru , Sasaki Kazuya , Suzuki Akihiro , Terai Takayuki
Published: September 2009

The oxygen isotope exchange and the time-of-flight secondary ion mass spectroscopy (TOF-SIMS) are used to visualize the oxygen pathway in a Ag cathode. It has been confirmed that oxygen is uniformly distributed on the subsurface of the Ag electrode, localized at the Ag grain boundaries in the Ag bulk, and uniformly distributed at the Ag/La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) interface. The oxygen pathway in the Ag electrode determined is as follows. Firstly, molecular oxygen is absorbed on the Ag surface and then dissociates into oxygen atoms. Secondly, these oxygen atoms diffuse along the grain boundaries from the Ag surface to the Ag/electrolyte interface. Thirdly, the oxygen atoms diffuse and spread along the Ag/electrolyte interface. Finally, oxygen ion transfer occurs across the two-dimensional interface between the Ag electrode and the electrolyte.
Electrode Properties of Pr0.7Sr0.3Fe0.8Al0.2O3-δ Thin Film Prepared by Pulsed Laser Deposition
Authors: Takahashi Hiroo , Takamura Hitoshi
Published: September 2009

A mixed conductive Pr0.7Sr0.3Fe0.8Al0.2O3-δ (PSFA) thin film has been prepared by using pulsed laser deposition (PLD) and its electrochemical properties have been investigated. A dense PSFA target for PLD was prepared at 1130 oC for 10 h. By using the target, 285 nm-thick PSFA thin film was deposited on an 8mol%Y2O3-doped ZrO2 substrate at 625 oC. The PSFA thin film was well crystallized and its grain size was in the range of 5 to 10 nm. The PSFA thin film showed an area specific resistance (ASR) of 0.37 Ω•cm2 at 900 oC. The activation energy of ASR was approximately 1.6 eV at temperature range of 600 to 900 oC.
Electrochemical Characterization of a La0.8Sr0.2Ni0.4Fe0.6O3-δ Electrode Interfaced with La9.83Si5Al0.75Fe0.25O26{plus minus}δ Apatite-type Electrolyte
Authors: Gasparyan Hripsime , Argirusis Christos , Szepanski Christian , Sourkouni Georgia , Stathopoulos Vassilis , Kharlamova Tamara , Sadykov Vladislav A. , Bebelis Symeon
Published: September 2009

The electrochemical characteristics of a La0.8Sr0.2Ni0.4Fe0.6O3 cathode electrode interfaced to La9.83Si5Al0.75Fe0.25O26{plus minus}δ apatite-type electrolyte were studied using AC impedance spectroscopy under open circuit conditions, at temperatures 600 to 800 oC and oxygen partial pressures in the range 0.1 to 20 kPa. The cathode and electrolyte powders were prepared via the Pechini method and the mechanochemical activation method, respectively. The electrocatalytic activity of the tested interface was assessed on the basis of its open circuit area specific polarization conductance , determined from the impedance data. The polarization conductance was found to increase with increasing , following power law dependence. The impedance characteristics of the system were determined by at least two different processes, corresponding to two partially overlapping depressed arcs in the Nyquist plots. The relative contribution and degree of overlap of these arcs depended on temperature and oxygen partial pressure.
Characterization of Cuprate based Cathode Structures by AC Impedance
Authors: Cassidy Mark , Irvine John
Published: September 2009

Composites containing the cuprate Nd1.8Ce0.2CuO4+δ (NCCO) have been shown to have promising behaviour for SOFC cathode applications, with performances similar to those of standard LSM based composites. It is hoped that the n-type conductivity exhibited by the NCCO may confer further operational advantages when operating at high oxygen utilizations or high cell polarisations where the local cathode oxygen partial pressure is reduced. Also, as it contains neither Mn nor Sr (both of which have been implicated in nucleating Cr deposition) it may also have benefits in terms of Cr tolerance. Candidate structures were assessed in a symmetrical half cell arrangement using both AC impedance and SEM examination. So far the best results have been obtained using the in-situ fired current collector Rp values of 0.10Ωcm2 and 0.115 Ωcm2 at around 750{degree sign}C have been observed for cathode structures with the CGO interface or CGO electrolyte respectively.
Ionic and Electronic Conductivity of (Ho0.9Ca0.1)2Ti2O6.9 Pyrochlore
Authors: Savvin Stanislav , Belov Dimitry , Shlyakhtina Anna , Shcherbakova Lidia , Ruiz-Morales Juan Carlos , Núñez Pedro
Published: September 2009

Partial electronic conductivity of (Ho0.9Ca0.1)2Ti2O6.9 was determined at 750-900C by Hebb-Wagner polarization and reoxidation methods. The ion transference number in air was estimated to vary from 0.991 at 750C to 0.979 at 900C. The activation energies of the electron and hole conductivity at P(O2)=1 atm were calculated to be 2.95 eV and 1.34 eV respectively.
Enhanced ASC Performance at 600{degree sign}C by Ceria Barrier Layer Optimisation
Authors: Van Berkel Frans P. , Zhang-Steenwinkel Ye , Schoemakers Guillaume , Van Tuel Marc , Rietveld B. G.
Published: September 2009

Reduction of the SOFC operating temperature to 600{degree sign}C is an effective approach for reducing the costs of applied materials and increasing the lifetime of SOFC systems. The anode-supported cell design (ASC) with thin electrolyte is a promising configuration for operation at this temperature. This paper deals with the ASC performance improvement at 600oC by optimisation of the ceria barrier layer that is placed between the La0.6Sr0.4CoO3-δ cathode and the zirconia electrolyte to prevent the formation of resistive secondary phases. Conventional screen printing has been used for the deposition of the ceria barrier layer. The improved screen printed ceria layer results in an increase in maximum power output of the anode supprted cell from 260 to 580 mW/cm2 at an operating temperature of 600oC. The performance improvement was mainly caused by a significant reduction of ohmic losses.
Bias-Assisted Sputtering of Gadolinia-Doped Ceria Interlayers for Solid Oxide Fuel Cells
Authors: Fonseca Fabio C. , Uhlenbruck Sven , Nedéléc Ronan , Sebold Doris , Buchkremer Hans Peter
Published: September 2009

The effects of both temperature and applied bias power during the sputtering of gadolinia-doped ceria (GDC) interlayers used as diffusion barriers in anode-supported solid oxide fuel cells (SOFC) were investigated. Scanning electron microscopy analysis revealed that increasing the applied bias power, in the 0-300W range, progressively inhibits the columnar structure typically observed in sputtered films, favoring the deposition of dense interlayers. Such feature was mirrored in the electrochemical tests of single cells that demonstrated enhanced power density for SOFC with bias-assisted sputtered interlayers. In addition, similar electrochemical performances of fuel cells having interlayers deposited in the 400-800 {degree sign}C temperature range indicated that the applied bias allows for the sputtering of GDC protective interlayers at relatively lower temperatures than unbiased depositions. The presented results evidenced that bias-assisted sputtering is an effective technique for the fabrication of high-performance anode supported SOFC.
Oxygen Incorporation Reaction into Mixed Conducting Perovskites: a Mechanistic Analysis for (La,Sr)MnO3 Based on DFT Calculations
Authors: Merkle Rotraut , Mastrikov Yuri A. , Heifets Eugene , Kotomin Eugene A. , Kukla Maija , Maier Joachim
Published: September 2009

Based on DFT calculations of intermediates and transition states, several hypothetical mechanisms for oxygen incorporation into mixed conducting La1-xSrxMnO3{plus minus}d perovskites are discussed. In the most probable mechanism, the rate-determining step comprises the encounter of a highly mobile surface oxygen vacancy and a molecular oxygen adsorbate. Starting from these results, the variation of reaction rates for different materials is explored.
Prediction of Surface Oxygen Vacancy Concentrations of (La1-xSrx)MnO3
Authors: Lee Yueh-Lin , Morgan Dane
Published: September 2009

Perovskite materials of the form ABO3 are an important family of compounds for use in solid oxide fuel cell (SOFC) cathodes. In particular, their surface properties play an essential role in their catalytic ability. This paper combines bulk defect models fit to experimental data with ab initio surface energies to predict surface vacancy concentrations in (La1-xSrx)MnO3. It is found that the surface vacancy concentration is ~106 times that of bulk under SOFC operating conditions. The enhanced concentration of surface vacancies may play a role in O2 dissociation, incorporation, and surface transport.
Investigation of Cathode Behavior and Surface Chemistry of Model Thin Film SrTi1-xFexO3-δ Electrode
Authors: Jung WooChul , Tuller Harry L.
Published: September 2009

The defect and transport properties of dense thin films of SrTi1-xFexO3-δ (STF), deposited by PLD onto single crystal YSZ and MgO substrates, were investigated based on the analysis of the chemical capacitance and the DC electrical conductivity as a function of temperature, pO2, and Fe fraction. The magnitude of the surface exchange coefficient, k, was found to be only weakly dependent on the magnitudes of the electronic and ionic conductivities as well as carrier densities (over nearly five orders of magnitude change in σel) over the x values (0.01-1.0) examined in this study. On the other hand, an appreciable degree of Sr-excess near the surface of the STF thin film was found by means of XPS over the whole Fe fraction from x=0.05-1.0. The observed defect, transport, and surface chemical properties are discussed in relation to the cathodic behavior of the STF thin film electrodes.
Investigation of the Oxygen Exchange Reaction on Pt/YSZ: The Relation between Three Phase Boundaries and Electrode Performance
Authors: Opitz Alexander K. , Schintlmeister Arno , Hutter Herbert , Fleig Juergen
Published: September 2009

In this work the electrochemical oxygen exchange reaction on the system platinum/yttria stabilized zirconia (YSZ) was investigated by means of impedance spectroscopy and time-of-flight secondary ion mass spectrometry (ToF-SIMS) on well-defined dense platinum thin film electrodes. From impedance measurements on differently sized electrodes it was possible to show that the resistance caused by the rate determining step scales with the inverse length of the three phase boundary (TPB). To reveal information on the properties of the electrochemically active zone - i.e. the zone where oxygen is incorporated into the electrolyte - 18O tracer experiments combined with ToF-SIMS analysis were carried out. The extension of the active zone was found to depend on the overpotential η. In addition, the ToF-SIMS investigations revealed an enrichment of impurities in the vicinity of the TPB after dc load. The influence of sample pretreatment on the electrode performance is discussed.
Potential Distribution in SOFCs with LSM and SYCM Cathodes Investigated Using a Built-in Potential Electrode
Authors: Burmistrov Ilya N. , Bredikhin Sergey I.
Published: September 2009

The objective of this work was to use a "built-in" potential electrode method to measure the cathode overpotential in solid oxide fuel cells (SOFCs) directly. The studies were performed on yttria-stabilised zirconia (YSZ) electrolyte-supported SOFCs using La0.8Sr0.2MnO3 (LSM) and Sr0.75Y0.25Co0.5Mn0.5O3-y (SYCM) as cathodes and Ni-ScSZ cermet as the anode. The contributions of the cathode, anode and electrolyte to the total cell resistance were investigated using a combination of current-voltage and impedance measurements with the built-in potential electrode technique. The cathode overpotential was shown to be lower for the SYCM cathode than for the LSM cathode, and the difference increases as the current in the cell increases.
Effect of Electrolyte Contribution on the Electrochemical Behaviour of Pr0.8Sr0.2Fe0.8Ga0.2O3
Authors: Ortiz-Vitoriano Nagore , Ruiz de Larramendi Idoia , Ruiz de Larramendi José Ignacio , Arriortua María Isabel , Rojo Teófilo
Published: September 2009

Pr0.8Sr0.2Fe0.8Ga0.2O3 (PSFG) phase with perovskite-type structure was obtained by a glycine nitrate process. The product was characterized by X-ray diffraction and an orthorhombic structure (Pbnm) was found. The study of morphology indicates the existence of inhomogeneous particle size and agglomerates. The polarization resistance was studied using different electrolytes: Yttrium-stabilized zirconia (YSZ); Samarium-doped ceria (SDC); Praseodymium-doped ceria (CPO) and Gadolinium-doped ceria (CGO). No chemical reactivity between the PSFG and the electrolytes was observed. Electrochemical Impedance Spectroscopy measurements of PSFG/electrolyte/PSFG test cells were carried out. These electrochemical experiments were performed at equilibrium from 850ºC to room temperature, under both zero dc current intensity and air. The obtained ASR values at 850ºC for the cell tests were: 0.67 Ω cm2 (YSZ); 0.55 Ω cm2 (SDC); 0.26 Ω cm2 (CPO) and 0.68 Ω cm2 (CGO).
A Global Defect Chemistry Model for p-Type Mixed Ionic and Electronic Conductors
Authors: Zhou Xiao-Dong , Anderson Harlan
Published: September 2009

A global defect chemistry model is presented to relate the properties of a variety of p type perovskite conductors, including chromites, manganites, and ferrites, which can be tailored as mixed ionic and electronic conductors (MIECs). It is found that oxygen nonstoichiometry in these p type MIECs can be correlated using reaction constant for oxygen vacancy generation. The values of reaction constant for oxygen vacancy formation can be obtained by simulating the electronic conductivity as a function of oxygen activity and temperature with the existing global model that is based on the concept of localized electron holes. The global defect chemistry model allows us to better understand and predict the electrochemical properties of perovskite type p-type conductors.
Fused LSM: A Novel Powder Limiting the Formation of La2Zr2O7 and SrZrO3 Resistive Phases at the Interface with YSZ in SOFC Cathodes
Authors: Levy Caroline , Zhong Yu , Morel Constance , Marlin Samuel
Published: September 2009

In solid oxide fuel cell (SOFC) on the cathode side, the formation of highly electrically resistive phases as La2Zr2O7 (LZO) or SrZrO3 (SZO) at the triple-phase boundary between LSM, YSZ and air decreases the performance of the cell and is partially responsible for the long term degradation of the SOFC. Saint-Gobain Company is making LSM material by fusion process. The reactivity of LSM made by fusion and conventional methods with 8YSZ was compared. Ageing tests were performed by increasing the temperature over 1100{degree sign}C and in several atmospheres (air and N2). Whatever the conditions are, the reactivity of fused LSM is barely if not observable whatever the Sr content is, whereas LSM powders made by conventional methods lead to the formation of LZO or SZO as a function of Sr content. Thus, LSM made by fusion process is a promising material for cathodes to avoid the long term degradation of SOFC.