bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of Tubular Solid Oxide Fuel Cells Composed of Ni-YSZ Supported SSZ Electrolyte Film and Cobaltile Electrodes for Reduced-Temperature Operating SOFCs
Authors: Nguyen Tuong Lan T. , Kato Tohru , Honda Takeo , Tanaka Yohei , Negishi Akira , Kato Ken , Tanaka Seiko , Iimura Youko
Published: May 2007

Tubular solid oxide fuel cells (SOFCs) composed of Ni- yttria- stabilized zirconia (YSZ) supported scandia-stabilized zirconia (SSZ) electrolyte film, doped ceria interlayer and strontium-doped cobaltile electrodes were successfully developed for reduced-temperature operation. The SOFCs were fabricated by adopting a slurry coating technique, which allows to prepare a ceramic layer with a thickness varied between 1~ca. 150μm, and a co-fire process. The fabrication process was investigated in detail for realizing low cost SOFCs with high degree of straight, round, high reproductive quality, and high electrochemical performance. Flawless dense electrolyte thin film less than 10μm was achieved on porous tubular Ni-YSZ substrate with the thickness that thicker than 500μm. Primary results of electrochemical performance test show that the a fabricated cells with (Sm0.6Sr0.4)CoO3 electrode could produce ca. 0.4 Wcm-2 of power density at H2 utilization of 60% at 800oC.
Performance of Single Cells with Anode Functional Layer based on Ni-YSZ, ScSZ and SDC for IT-SOFCs
Authors: Park Jae-Keun , Yang Su-Yong , Lee Taehee , Park Tae Seung , Yoo Young-Sung
Published: May 2007

To improve the performance of the anode-supported Solid Oxide Fuel Cells (SOFCs) which can be operated at an intermediate temperature, the functional layer (FL) is introduced on a Ni- YSZ anode substrate. And the scandia-stabilized zirconia (ScSZ) and the samaria-doped ceria (SDC) which have the high ionic conductivity and the chemical stability as well as the yttria- stabilized zirconia (YSZ) are used as material for the anode FL with the Ni. The fabrication process of anode-supported single cell with the anode FL was established and the power density of those was appreciated. As a result, the sample with anode FL (Ni-YSZ) has higher power density than normal cell. The single cell which was consist of the FL(Ni-YSZ) and a electrolyte(YSZ) showed about 550mW/cm2 as the maximum power density and 0.41Ω cm2 as a lower internal resistance at 650{degree sign}C. In case of the single cell using the ScSZ and the SDC as the anode FL, the performance of samples decrease rapidly and those showed unstable voltages during long-term test.
Power Generation Experiment of Single Planar SOFC with Segmented Electrodes
Authors: Iwai Hiroshi , Yasutomi Ryota , Okumura Youji , Saito Motohiro , Yoshida Hideo , Kodani Kazufumi , Yoshikata Kuniaki
Published: May 2007

Power generation experiments with single planar solid oxide fuel cell were conducted. Two types of cells with different electrolyte material, namely Yttria Stabilized Zirconia (YSZ) and Gadolinia Doped Ceria (GDC), were tested. Both the anode and cathode electrodes were segmented so that the local current density could be obtained. Fundamental power generation characteristics of the test cells are evaluated varying the operation temperature and the hydrogen concentration in the fuel flow. The local current densities are successfully measured within the space resolution of the segmented electrodes, showing the possibility of measuring the local current density distribution of a cell under operation.
Fabrication and Characterization of the Gas Channel Integrated SOFC Cells
Authors: Ryu Takashi , Okamoto Taku , Chen Chunhong , Ito Shigenori , Matsuda Kazuyuki , Kuno Toshiaki , Ichigi Takenori
Published: May 2007

The unique anode supported solid oxide fuel cell called gas channel integrated cell is introduced in this paper. The cell has the flat-tubular structure with the appearance of the planar cell, therefore has the great advantage in the volumetric power density. The cell was fabricated by molding the planer anode substrate with the gas channel preform and burning out it during the firing process. The entire surfaces of the anode substrate are covered with the thin film electrolyte and the cathode layers are printed on the both electrolyte surface. The fabricated cells have the size of 10 cm x 11 cm and 2mm in thickness. The electric power generation was implemented with the single cell at 800{degree sign}C with the hydrogen. The generated power of 30 W was comparable to that in the conventional planar cell.
Fabrication and Characterization of Miniaturized SOFC by Colloidal Process
Authors: Oh Eun Ohk , Kim Hyoungchul , Baek Dong Chul , Park Junyoung , Kim Hae-Ryoung , Lee Jong-Ho , Lee Hae-Weon , Whang Chin Myung , Son Ji-Won
Published: May 2007

Miniaturized solid oxide fuel cells (SOFCs) have drawn increasing interest as next generation portable and mobile power sources recently. For these applications, operation and fabrication temperature reduction along with miniaturization of SOFCs should be achieved. For these purposes, we investigated miniaturized SOFC fabrication through various processing techniques including colloidal processes. Anode- supported cells with thin electrolytes and well-controlled electrode structures are obtained by the combination of the processes such as spin-on, electrostatic spray deposition, and microwave sintering at lower fabrication temperature. The properties of cell components and the overall cell performance have been characterized and will be presented.
Characteristics and Performance of Electrolyte Supported Single Solid Oxide Fuel Cells using Ethanol and Hydrogen
Authors: Zanetti de Florio Daniel , Fonseca Fabio Coral C. , Muccillo Eliana N. , Muccillo Reginaldo
Published: May 2007

A laboratory setup was designed and put into operation for the development of solid oxide fuel cells (SOFCs). The whole project consisted of the preparation of the component materials - anode, cathode, and electrolyte - and the buildup of a fuel leaking-free sample chamber with platinum leads and current collectors for measuring the electrochemical properties of single SOFCs. Several anode powders of ZrO2:Y2O3 + NiO or GDC + NiO, obtained by solid state mixture, modified liquid mixture and commercial one have been wet sprayed on electrolyte supported single SOFCs consisting of porous anode / (ZrO2:Y2O3) dense electrolyte / (La0.65Sr0.35MnO3 + ZrO2:Y2O3) porous cathode. These cells have been tested at 600 {degree sign}C, 700 {degree sign}C, 800 {degree sign}C and 900 {degree sign}C after in situ H2 anode reduction, using ethanol or H2 as fuels. The main results show that the wet spraying coating method resulted in single-cells with good reproducibility and reasonable performance.
Metal-supported Solid Oxide Fuel Cell Operated at 400~600{degree sign}C
Authors: Hui Shiqiang R. , Yang Dongfang , Wang Zhenwei , Yick Sing , Decès-Petit Cyrille , Qu Wei , Tuck Adam , Maric Radenka , Ghosh Dave
Published: May 2007

Metal-supported SOFCs potentially offer many advantages compared to conventional technology, such as low operating temperatures, reduced cost, and increased reliability. They are also a promising choice for applications that require quick start-up, good stability against thermal cycles and mechanical shock resistance such as Auxiliary Power Units (APU) for the automotive industry. The National Research Council of Canada's Institute for Fuel Cell Innovation (NRC-IFCI) has been working on the development of metal supported SOFCs since 2004. In this paper, a metal-supported SOFC with a samarium doped ceria (SDC)/scandia-stabilized zirconia (ScSZ) bilayer electrolyte was fabricated by a combination of pulsed laser deposition (PLD) and wet chemistry processing. The cell performance and aging characteristics were analyzed by AC impedance spectroscopy and current-voltage measurements during operation in the temperature range from 400oC to 600oC. The power generation characteristics at low temperatures of this metal- supported SOFC will be beneficial for quick start-up and is expected to alleviate the performance deterioration. These results at such an early stage of research is very promising for the future development of this technology.
Fabrication of a Metal-Supported Ceria Cell by Wet Powder Spray and its Characterization at Intermediate Temperatures
Authors: Oishi Naoki , Yoo Yeong , Davidson Isobel
Published: May 2007

A tri-layer comprising a lanthanum strontium cobalt iron perovskite cathode, a doped ceria electrolyte and a nickel ceria cermet anode was fabricated on a porous stainless steel substrate by a series of processing technologies of wet powder spraying, lamination and sintering, and was tested under fuel cell conditions of humidified 50 % hydrogen and air at intermediate temperatures of 650 and 600 {degree sign}C. Open circuit voltage showed relatively lower values, below 0.75 V, the cell was found to deliver higher current densities over 1 A/cm2, achieving a maximum density of over 450 mW/cm2 at 650 {degree sign}C. It was found that the cathode accounted for most of the polarization resistance and that the anode polarization was less influential to the ceria cell tested.
Spray Pyrolysis Deposition of Electrolyte and Anode for Metal Supported Solid Oxide Fuel Cell
Authors: Xie Yongsong , Neagu Roberto , Hsu Ching-Shiung , Zhang Xinge , Decès-Petit Cyrille
Published: May 2007

Metal supported solid oxide fuel cells offer many advantages including increased robustness, improved thermal shock resistance and decreased cost. However, fabricating metal- supported solid oxide fuel cells using conventional techniques are either very difficult or very costly. In this study, two processes of spray pyrolysis deposition - pneumatic spray deposition and electrostatic spray deposition were used to deposite samaria doped ceria (SDC) electrolytes on different substrates and deposite NiO-SDC anodes on porous stainless steel substrate. A cathode layer was subsquently applied on the electrolyte by stencil prining for electrochemical testing. The test results indicaed that the electrolyte had reasonable cell performance but the topography of the anode needed optimization.
Stability Analysis of the Interface Between Electrical Contact Layers and Metal Interconnects in Solid Oxide Fuel Cells
Authors: Shim Sungbo , Mumm Daniel R.
Published: May 2007

Growth of an oxide layer between the metallic interconnect and cathode leads to undesirable increases in contact resistance across the interface. It is particularly important to minimize the interfacial resistance by using suitable electrical contact layer between cathode and interconnect. In order to develop ideal electrical contact layer, fundamental mechanism of the evolution of interface between electrical contact and metallic interconnect in SOFC cathode environment was studied. ASR evolution of LaNi0.6Fe0.4O3 (1) and Pt contact layer/Pt sheet interface was evaluated. It was found that interdiffusion plays a key role in ASR increase. Particle sintering was minimal after 200 hours. Smaller particle size of LNF electrical contact layer enhanced diffusion rate to the scale. ASR of growing oxide was measured with Pt and LNF electrode. Interdiffusion between electrical contact material and growing oxide was observed and contributed to ASR increase rate. It seems that development of electrical contact material that reacts with oxide scale and forms the phase that has low resistance is a direction to pursue.
Carbon Content in a Direct Carbon Fuel Cell
Authors: Jain Sneh , Lakeman Barry , Pointon Kevin D. , Irvine John T.
Published: May 2007

In direct carbon fuel cells (DCFCs), elemental carbon is directly oxidised electrochemically to generate electrical power. Carbon is readily available, easily transported and stored and, therefore, affordable to the global energy economy. Further operational advantages include the use of a fully renewable solid bio-carbon fuel source and the opportunity for scale-up. Herein we discuss a DCFC which utilises a molten mixed alkali metal carbonate eutectic as a secondary electrolyte, contained within a solid oxide fuel cell. The operation of the cells over an extended temperature range (525-700 oC) was examined using standard electrochemical methods. We will present the electrochemical performance of Super S, a high surface area carbon black.
High-temperature Reactions between Scandia-doped Zirconia (ScSZ) and Cathode Materials
Authors: Wackerl Jürgen , Markus Torsten , Peck Dong-Hyun , Woo Sang-Kuk , Singheiser Lorenz
Published: May 2007

The high-temperature reactions of some familiar cathode materials like strontium doped lanthanum manganite (LSM), strontium doped samarium manganite (SSM) and strontium and cobalt doped lanthanum ferrite (LSCF) with a 10 mol% scandium doped zirconia (10ScSZ) electrolyte material were investigated. After annealing the mixtures of cathode and electrolyte materials for 100 hours at 1200 {degree sign}C in air, the LSM- ScSZ and the SSM-ScSZ mixtures remained biphased. Nevertheless, the LSM shows a better adhesion with the ScSZ compared to the SSM. This is due to the formation of pores at the SSM-ScSZ interface. The formation of a tetragonal zirconia phase was observed in combination with SSM. This situation remains unclear for the LSCF-ScSZ mixture due to the presence of secondary phases. Among these is one having a good adhesion to the ScSZ. Additionally, a CoFe2O4 spinell was found for the LSCF.
Influence of Polymeric Resin-Derived LSM Coated YSZ Composites on Cathodic Performance and Durability in SOFCs
Authors: Song Hwa Seob , Hyun Sang-Hoon , Moon Jooho
Published: May 2007

(La, Sr)MnO3 (LSM) - yttria doped ZrO2 (YSZ) composite was prepared using polymeric resin-derived LSM precursor coated on the YSZ particles in order to improve the performance and durability of SOFC cathode. The synthesized LSM-YSZ composite powder was confirmed by XRD, XPS, and SEM. The cathodic performance of the symmetrical electrochemical cell with different LSM-YSZ ratios was investigated by measuring impedance spectroscopy. There was an optimum ratio at which cathodic polarization was minimized because of better homogeneity, longer triple-phase boundary, and sufficient ionic conductivity. Cyclic current loading test was further carried out for rapid evaluation of aging effect of coated composite cathode, which was compared with mechanically mixed LSM-YSZ powder.
Growth of Thin Film Electrodes of SOFC by PLD Method
Authors: Tsukui Shigeki , Otani Masashi , Yoshida K , Sagara K , Oka T
Published: May 2007

Thin films of cathode and anode electrode were prepared by pulsed laser deposition. High porosity and good conductivity cathode film (Gd0.5Sr0.5CoO3) was grown at 1023 K on YSZ(100) single crystal. The electric conductivity was 640 S/cm at 1123 K in air. High porosity and good crystalline anode thin film (Ni-YSZ cermets) was grown at over 1023 K.
ONEBAT: Micro-Solid Oxide Fuel Cells for Battery Replacement in Portables
Authors: Rupp Jennifer , Muecke Ulrich P. , Beckel Daniel , Bieberle-Hütter Anja , Infortuna Anna , Gauckler Ludwig J.
Published: May 2007

The Swiss ONEBAT project aims for the fabrication of micro- Solid Oxide Fuel Cells. This are miniaturized solid oxide fuel cells in which the active fuel cell components (anode, electrolyte and cathode) exist as thin films forming a free- standing membrane on a substrate. The total thickness of the fuel cell membrane is less than 2 micrometer in thickness and of 200 micometer in diameter. Heat cycling between room temperature and 550 {degree sign}C are possible for such membranes without rupture or crack development. The future goal is to integrate these micro-Solid Oxide Fuel Cells in a system with reformer, post-combuster and insulation, and to replace current Li-ion batteries. Microstructure and electrical conductivity characteristics of micro-solid oxide fuel cell gadolinia-doped ceria thin film electrolytes are reported more detailed in this study.
Ceria-Based Thin Film Hetero-structure Growth and Characterization for SOFC Applications
Authors: Esposito Vincenzo , Pergolesi Daniele , Sanna Simone , Tebano Antonello , Medaglia Pier Gianni , Licoccia Silvia , Balestrino Giuseppe , Traversa Enrico
Published: May 2007

Electrolyte thin films of Ce0.8Gd0.2O1.9-δ (GDC20) ionic conductor were deposited by pulsed laser deposition (PLD) for the fabrication of micro solid oxide fuel cells (SOFCs). The crystal structure and morphology of the films deposited on different substrates were investigated as a function of the growth parameters, using X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) analysis. The film conductivity was measured in parallel and perpendicular directions of the film substrate using electrochemical impedance spectroscopy (EIS) measurements. Pt or La0.8Sr0.2Co0.8Fe0.2O3-δ (LSCF) films were used as electrodes in symmetrical cells. For parallel conductivity measurements, two electrodes were deposited by PLD on the surface of the film, while for perpendicular conductivity, thin film hetero- structure were grown sandwiching the electrolyte film between the two electrodes.
Materials for Symmetrical Solid Oxide Fuel Cells
Authors: Ruiz-Morales Juan Carlos , Canales-Vázquez Jesús , Savaniu Cristian , Irvine John T. , Núñez Pedro
Published: May 2007

A new concept of Solid Oxide Fuel Cell (SOFC), Symmetrical SOFC (SFC), has been investigated. In this new configuration, the same electrode material is used simultaneously as anode and cathode. Interconnector materials, such as chromites, could be potential symmetrical electrodes, at least, under pure hydrogen at relatively high temperatures. However, their lack of catalytic activity towards hydrocarbon oxidation led to the use of substituted-chromites to enhance the aforementioned catalytic activity. Thus, La0.75Sr0.25Cr0.5Mn0.5O3-δ (LSCM) is a good option for such symmetrical configuration, rendering fuel cell performances in excess of 500 and 300mW/cm2 using pure H2 and CH4 as fuel, at 950oC. Other potential materials could be typical n-type anode materials, such as strontium titanates, that could be activated for oxidising conditions by substituting some of Ti content for Fe to introduce p-type conductivity. Preliminary electrochemical experiments on La4Sr8Ti12-xFexO38-δ-based SFCs show that they perform reasonably well under humidified H2.
Manufacture of LSM and GDC Thick Film Pastes for SOFCs in an ISO 9001 Environment
Authors: Feingold Alvin H. , Palanisamy Ponnusamy , Takarabe Kunihide , Topka Zak , Webb Richard S.
Published: May 2007

Availability of SOFC materials for cell fabrication in the desired form (tape, paste, etc.) is crucial. Equally important is the dependable supply of these products with consistent properties despite of size of volume. This paper discusses successful development, scale-up, and manufacture of those materials.
Development of High-Performance Current Collectors via Novel Metal Coating for Micro-Tubular Cells
Authors: Liu Yu , Hashimoto Shin-Ichi , Nishino Hanako , Takei Katsuhito , Mori Masashi , Funahashi Yoshihiro
Published: May 2007

The Ni-cermet anode-supported micro-tubular SOFC based on La0.6Sr0.4Co0.2Fe0.8O3-d cathode shows high power density below 650{degree sign}C. Current collecting appears to a major obstacle towards the integration of these single cells in a cube-shaped cell bundle, which can finally lead to a higher volumetric power density. This study aims to develop and modify for high performance current collectors for the compact and high power SOFC bundles. Feasibility of the La0.6Sr0.4Co0.2Fe0.8O3-d based oxides was then investigated. The well-dispersed Ag particles were introduced to give an enhanced electron path and a lowed interfacial resistance.
Solid Oxide Electrolyzers for Efficient Hydrogen Production
Authors: Ouweltjes Jan Pieter P. , Tuel Marc V. , van Berkel Frans P. , Rietveld Bert
Published: May 2007

Solid oxide electrolyzers have the potential to play an important role in a hydrogen economy in which energy, for mobile applications and electrical grid load balancing, is stored as hydrogen. The advantages of solid oxide electrolyzers for hydrogen production are 1/ the high operating temperature resulting in high electrical efficiency, 2/ the possibility to use hydrocarbon fuels as counter-feed to further increase the electrical efficiency, and 3/ the flexibility to alternately operate in fuel cell mode. This paper focuses on the use of state-of-the-art SOFC materials for air-assisted and hydrocarbon-assisted hydrogen production. Electrolyte supported cells, with 90 µm thick 3YSZ electrolyte and Ni-GDC electrode, showed comparable ASR-values in electrolyzer and fuel cell mode between 650 and 920{degree sign}C, and exhibited stable hydrogen output during a 100 hours period in both electrolyzer modes at 850{degree sign}C and 70% steam utilization. Anode supported cells, with 5µm thick 8YSZ electrolyte and Ni- YSZ electrode, showed lower ASR-values than electrolyte supported cells, which would make this cell type the most promising. However, in this case the hydrogen production was limited at steam utilizations of 50%, which seems related to mass transport limitations in the anode substrate.
Single-Chamber Mini-Solid Oxide Fuel Cells Operated at a Lower Temperature
Authors: Min Ji-Hyun , Ahn Sung-Jin , Moon Jooho , Kim Joosun , Lee Hae-Weon
Published: May 2007

The performance characteristics of single chamber solid oxide fuel cell (SOFC) with micro-patterned electrode structures on the disc type electrolyte were investigated. We selected Sm0.2Ce0.8O2-x (samarium doped ceria, SDC) as an electrolyte, SDC-NiO cermat as an anode and SDC-Sm0.5Sr0.5CoO3(samarium strontium cobaltite) as a cathode for low operating temperature (500-600{degree sign}C). To fabricate complex micro-patterned electrodes on electrolyte, we used microfluidic lithography method. Before patterning the cathode, patterned NiO-SDC anode sintered at 1350{degree sign}C for 4 hrs, then SDC-SSC cathode was patterned and sintered at 1050{degree sign}C for 8 hrs, resulting in co- planar type single chamber SOFC in which interdigitated electrode has 100 μm line width with anode-to-cathode distance 100 μm. Reduction condition was proposed below 350{degree sign}C using humidified hydrogen gas. The shape of electrode and microstructure was observed by scanning electron microscope (SEM) and optical microscope. I-V characteristics of the SOFC were measured using a propane-air mixture gas by DC source measure unit.
Single-Chamber SOFC Operating with Hydrocarbon-Air and Hydrogen-Oxygen Gas Mixtures
Authors: Kellogg Isaiah , Dogan Fatih , Suzuki Toshio , Koylu Umit O. , Anderson Harlan U. , Petrovsky Vladimir
Published: May 2007

A single-chamber solid oxide fuel cell (SC- SOFC), which is operated in a mixture of fuel and oxidant gas, provides several advantages over the conventional SOFC such as simplified cell structure (no sealing required). SC-SOFC allows using a variety of fuels without carbon deposition by selecting appropriate electrode materials and cell operating conditions. Operating conditions of single chamber SOFC was studied using hydrocarbon- air gas mixtures for a cell composed of NiO-YSZ/YSZ/LSCF-Ag. The cell performance and catalytic activity of the anode was measured at various gas flow rates. The results showed that the open-circuit voltage and the power density increased as the gas flow rate increased. A similar cell was tested in a double chamber configuration using hydrogen-air mixtures by controlling the hydrogen/air ratio at cathode and anode. Simulation of single chamber conditions in double chamber configurations allows distinguishing and better understanding of the electrode reactions in the presence of mixed gases. The effect of hydrogen-air mixtures as a fuel on the performance of anode and cathode materials in single-chamber and double- chamber SOFC configurations is presented.
Anode Performance of a Dense Pd Film for IT-SOFCs using BaCe0.8Y0.2O3-α as an Electrolyte
Authors: Asano Koichi , Kawakami Masashi , Mugikura Yoshihiro , Watanabe Takao
Published: May 2007

We evaluated the anode performance of a dense Pd film for intermediate temperature-type solid oxide fuel cells (IT-SOFCs) using BaCe0.8Y0.2O3-a (BCYO) at 723 to 873 K. A dense Pd film anode of diameter 13 mm was fabricated by electroless plating deposition onto a BCYO substrate (diameter: 17 mm, thickness: 0.5 mm) and heat treatment at 1123 K after the plating. The anodic overvoltage hardly changed even when the film thickness was increased. An interfacial specific resistance of 0.05 ohm cm2 was achieved at 823 K in the dense Pd film anode in a pure hydrogen atmosphere. In dense film and porous electrodes, the apparent activation energies were 89 kJ mol-1 and 86 kJ mol-1, respectively, which are almost identical values. These results suggest that the dense Pd film possesses sufficient anodic reactivity for IT-SOFCs using a protonic conductor such as BCYO.
Characterisation of Combinatorial Libraries of Perovskite Materials for SOFC Cathode Applications
Authors: Rossiny Jeremy , Fearn Sarah , Kilner J.A. A. , Zhang Yong , Chen Lifeng , Yang Shoufeng , Evans Julian R. , Zhang Tong , Yates Karen , Cohen Lesley F.
Published: May 2007

The system La0.8Sr0.2Mn1-xCoxO3+δ (LSMC) for 0{less than or equal to}x{less than or equal to}1 with x varying by 0.1 has been synthesised by the means of a robotic ink-jet printer. Characterization of the materials has been implemented to determine the non-stoichiometry, structure and composition of each sample. Raman spectroscopy has been used to study the B-site metal/oxygen interactions.
(BaxSr1-x)(CoyFe1-y)O3-δ Perovskites as SOFC Cathode Material: Electrode-Electrolyte Reactions and Electrochemical Characterisation
Authors: Wang Lei , Merkle Rotraut , Baumann Frank S. , Fleig Jürgen , Maier Joachim
Published: May 2007

(BaxSr1-x)(CoyFe1-y)O3-d (BSCF) perovskites are promising SOFC cathode materials. The interfacial reaction with zirconia and ceria electrolyte materials is investigated. The electrochemical performance is studied for y = 0.8, x = 0.25 and 0.5, using im-pedance spectroscopy on dense thin-film microelectrodes, which allows one in particular to determine absolute values of the surface resistance unaffected by morphology effects. Temperature, oxygen partial pressure and applied DC bias are varied to obtain a broad data basis for a further mechanistic analysis.
Long-Term Stability of Composite Cathode at High Current Densities
Authors: Kusnezoff Mihail , Trofimenko Nikolai , Mosch Sindy , Beckert Wieland , Graff Andreas , Altmann Frank
Published: May 2007

The durability tests were carried out on substrate supported cells based on yttria and scandia stabilized zirconia with conventional uLSM/YSZ and Ni/YSZ electrodes. The cells were operated at 850{degree sign}C in air/H2:H2O (1:1) for more than 1000h at current densities >450 mA/cm2. The reduction of the cathode polarization resistance is observed from the analysis of the impedance spectra. Microstructure investigations of the composite cathode using FESEM and TEM were made. It was found that the composite cathode undergoes morphology changes during the first 200-500h of the operation creating some nano-porosity at the uLSM/YSZ interface. Furthermore it was found that the change of the microstructure is strongly affected by the magnitude of the current density. The depth of the electrochemically structured zone as well as the change of the uLSM-composition at the uLSM/YSZ-interface was investigated using transmission electron microscopy.
Impedance Studies of Thin-film and Patterned Sr-doped LaMnO3 on Yttria- Stabilized Zirconia to Probe Oxygen Reduction Kinetics
Authors: La O' Gerardo Jose , Shao-Horn Yang
Published: May 2007

Sr-doped LaMnO3 (LSM)/Yttria-stabilized Zirconia (YSZ) are the conventional cathode/electrolyte materials for SOFCs. However, the mechanisms that occur during oxygen reduction reaction (ORR) at the cathode/electrolyte interface are still unclear and have been a roadblock for further enhancement of SOFC performance, especially at low-temperatures. For this study, LSM is fabricated on sputtered and single crystal YSZ by thin-film techniques and patterned via photolithography to obtain precise microelectrodes. EIS results on thin-film LSM microeletrodes supported on thin-film YSZ showed at least four distinct processes during ORR, which were tentatively assigned to (i)surface chemical reaction on LSM, (ii)surface diffusion on LSM, (iii)electrolyte ion transport and (iv)bulk+three-phase boundary (TPB) charge transfer process. It should be noted that the resistance associated with bulk+three-phase boundary charge transfer was highly dependent on LSM electrode thickness. In contrast, thin-film LSM microelectrodes supported on single-crystal YSZ exhibited one distinct process, which is be attributed to bulk charge transfer process.
Deconvolution of SOFC Cathode Polarization
Authors: Wachsman Eric
Published: May 2007

Current SOFC performance is limited primarily by cathode polarization. In order to address this we have undertaken a multi-faceted, multi- disciplinary approach to deconvolute the various contributions to SOFC cathode polarization. This approach involves using catalysis techniques to determine the fundamental oxygen reduction mechanism, using a FIB/SEM to quantify the cathode microstructure, and relating kinetics and microstructure to electrochemical performance. The results to date are summarized.
Mechanisms and Rate Laws for Oxygen Exchange on Mixed-Conducting Oxide Surfaces
Authors: Adler S.B. , Chen Xiyong Y. , Wilson Jamie R.
Published: May 2007

Although the thermodynamic and transport properties of mixed-conductors are generally understood, a consensus has not emerged regarding the mechanisms (and appropriate rate laws) governing exchange of oxygen with the bulk at the gas-exposed surface. One difficulty is that mass-action rate expressions typically used in developing kinetic models are at odds with the thermodynamic behavior, which often deviates substantially from mass-action. We have developed an alternative framework for deriving O2 reduction rate laws that is rigorously consistent with thermodynamics, yet allows rates of some individual steps to be developed in terms of traditional mass-action laws, where appropriate. We have used this framework to re-examine equilibrium oxygen exchange kinetics reported for electron-rich perovskite mixed conductors La1-xSrxCoO3-δ (LSC) and La1- xSrxFeO3-δ (LSF). Our analysis suggests that the metallic band structure of LSC may play an important role in the catalysis by stabilizing physisorbed O2 on the surface.
Influence of Cathode Porosity and Potential on Oxygen Reduction Kinetics at Intermediate Temperature SOFCs Cathodes
Authors: Lust Enn , Kivi Indrek , Nurk Gunnar , Möller Priit , Kallip Silvar , Grozovski Vitali , Kurig Heisi
Published: May 2007

Electrochemical characteristics of half-cells, based on gadolinia doped ceria electrolytes and micro-mesoporous La0.6Sr0.4CoO3-δ, Pr0.6Sr0.4CoO3-δ and Gd0.6Sr0.4CoO3-δ cathodes, have been obtained by electrochemical impedance, cyclic voltammetry and chronoamperometry methods. The seeming activation energy Eact depends on the chemical composition of half-cell, specific surface area and pore size distribution inside the cathode. Eact decreases with increasing negative potential, and more pronounced dependence of Eact on potential has been established for less porous cathodes. The transfer coefficient for the oxygen reduction reaction αc > 0.5 dependent on the half-cell has been obtained. Analysis of Nyquist and Bode plots indicates the complicated adsorption/absorption and mass transfer processes inside the porous material at temperature T {greater than or equal to} 773 K. At T{greater than or equal to} 873 K the limiting step is the charge transfer process. Dependence of the ratio of limiting steps on cathode porosity and chemical composition as well as on electrode potential and temperature was established.
Development of (La0.75Sr0.25)(Cr0.5Mn0.5)O3 Cathodes of Solid Oxide Fuel Cells by Gelcasting Technique
Authors: Jiang San Ping , Zhang Lan , Cheng C. S. , Zhang Lan
Published: May 2007

The synthesis and performance of (La0.75Sr0.25)Cr0.5Mn0.5O3 cathodes of solid oxide fuel cells (SOFCs) by gel-casting and solid-state reaction methods were investigated. DTA and XRD analysis indicate that the phase formation temperature of LSCM powders synthesized by the gel-casting technique is 50-100oC lower than that by the solid-state reaction method. The reason is related to the homogeneously distributed and immobilized precursor particles in a polymeric network, achieved during the cross linking and gel formation steps. The LSCM cathode prepared by the gel-casting powder is shown to have a much higher electrochemical activity for the O2 reduction than that by the solid-state reaction powder. The results in the present study demonstrate the advantages of the aqueous gel-casting method in the synthesis of high quality and highly catalytic active perovskite LSCM oxide powders for SOFC cathodes.
Studies of Oxygen Exchange on Thin-Film La0.6Sr0.4CoO3-δ Using Nonlinear Electrochemical Impedance Spectroscopy (NLEIS)
Authors: Wilson Jamie R. , Sase Maya , Kawada Tatsuya , Adler S.B.
Published: May 2007

In order to probe the mechanism of O2 reduction on mixed- conducting oxides, we have measured the nonlinear harmonic impedance response of a dense thin film electrode of La0.6Sr0.4CoO3-δ. (LSC-64). This approach reveals the nonlinear rate law governing O2 reduction/oxidation. Comparison to various models based on nonequilibrium thermodynamics suggests that O2 reduction on LSC-64 is limited by dissociative adsorption. These results are discussed in the context of known equilibrium exchange kinetics and electronic structure. Implications for porous electrode kinetics are also discussed.
Electrochemical Characterization of Air Plasma Sprayed LSM/YSZ Composite Cathodes on Metallic Interconnects
Authors: White Bradley , Kesler Olivera , Rose Lars
Published: May 2007

Porous composite cathodes composed of (La0.8Sr0.2)0.98MnO3-y (LSM) and yttria stabilized zirconia (YSZ) have been produced by axial air plasma spraying on porous metal interconnect substrates and characterized by scanning electron microscopy (SEM). Cathodes with different microstructures were produced by varying the input parameters of the APS process to determine the effect of this variation on cathode microstructure and performance. Symmetrical double-cathode cells with YSZ electrolytes produced by plasma spraying were also fabricated for comparison of electrochemical performance at temperatures ranging from 650{degree sign}C to 900{degree sign}C, using electrochemical impedance spectroscopy (EIS) to correlate the microstructural quality with the cathode polarization resistance. Values of the APS process parameters most suitable for the deposition of LSM/YSZ composite cathodes were identified, and post-testing analysis of the symmetrical cells was carried out to examine the degradation of the metal substrate and cathodes.
Alanine Assisted Low-Temperature Synthesis and Characterization of Nanocrystalline SOFC Cathodes
Authors: Basu Rajendra , Pal P , Raja M W. , Mukhopadhyay J , Dutta A , Mahanty S , Maiti H S.
Published: May 2007

Nanocrystalline SOFC cathode materials of perovskite family, La1-xSrxM1-yCoyO3, where 0<x{less than or equal to}0.5, 0<y {less than or equal to}0.8 (M is transitional metal= Mn or Fe) have been synthesized at a relatively low temperature by combustion technique using alanine as novel fuel. The thermal analyses of the precursor gels show sharp single step combustion with low decomposition temperature (170- 200oC). Detailed X-ray powder diffraction analyses show 47-96% phase purity in the as-synthesized powder and upon calcination at temperature ~ 825oC, single phase material is obtained wherein the nanocrystallinity (crystallite size ~19-24 nm) is retained. Densification studies of the materials are carried out within 900-1100oC. The coefficient of thermal expansion (CTE) of the sintered cathodes is also measured. Detailed electrical characterizations of the sintered cathodes are evaluated and correlated with the microstructures. The electrochemical performances of SOFC single cells (Ni-YSZ anode-support /YSZ ~ 20 μm/LaFeO3-based cathodes) with ceria interlayer show high current density of ~1.2 A/cm2 at 0.7V at 8000C.
Correlation of La0.8Sr0.2MnO3-δ Powder Synthesis Routes and High Temperature Electrical Properties
Authors: Creedon Matthew. J. , Yang Yi , Khadilkar Chandra S. , Shaikh Aziz
Published: May 2007

Lanthanum strontium manganate (LSM) powders were synthesized utilizing high temperature solid-state calcination and co-precipitation methods. The powders were characterized by various techniques such as by X-Ray diffraction (XRD), BET surface area, laser scattering particle size analyzer, scanning electron microscopy (SEM), and ICP spectrometer. Selected LSM powders were then formulated to make tapes of various thickness. Tape layers were laminated and fired to form a dense substrate of LSM. The temperature dependence of electrical conductivity of fired substrates was measured using four-point probe method. The correlation between the powder synthesis route and the electrical properties is investigated.
Evaluation of La0.8Sr0.2Cu1-xMnxOd Double Perovskite for Use in SOFCs
Authors: Berenov Andrey , Wood Hilary , Atkinson Alan
Published: May 2007

Compounds with the general formula La0.8Sr0.2Cu1-xMnxO3 were prepared by the citrate route. A solid solution region containing hexagonal perovskite phase, was formed when 0.6{less than or equal to}x{less than or equal to}1, in which oxygen stoichiometry in air changes from oxygen deficiency to oxygen excess with Mn doping. The temperature dependence of electrical conductivity changes from metallic- like behavior in La0.8Sr0.2CuO3-d to semiconducting type in La0.8Sr0.2MnO3+d. Mn doping resulted in a decrease in the conductivity (with the minimum at 40% Mn doping), whereas the thermal expansion coefficient decreased linearly with x. A defect model for the mixed Cu-Mn perovskite is proposed and related to its physical and electrochemical properties.
LaNi0.6Fe0.4O3 - Ceria Composite Cathode for SOFCs Operating at Intermediate Temperatures
Authors: Chiba Reiichi , Orui Himeko , Komatsu Takeshi , Tabata Yoshitaka , Nozawa Kazuhiko , Arai Hajime , Arakawa Masayasu , Sato Kazunori
Published: May 2007

We fabricated single cells with the LaNi0.6Fe0.4O3 cathode and scandia alumina doped zirconia electrolyte. Cells with a cathode consisting of current collecting LNF layer and active layer were also fabricated by using the screen printing technique. The active layer contains SDC or GDC and LNF particles. The LNF cathodes with this active layer exhibited good levels of performance including over potential and interface resistance from the start of the operation at 800C. With this configuration, adhesiveness of the cathode to the zirconia electrolyte was improved as well. It was found that the active layer is functional, when the ceria particle size is smaller or equal to that of LNF. SEM observation of the active layer shown high sintering temperature tends to break weak bonds around triple phase boundary and create strongly connected bonds of LNF and ceria particles in the active layer.
A-Site Deficiency and Phase Purity of Lanthanum Strontium Ferrite Powders
Authors: Striker Todd , Ruud James A. , Heward William J. , Gao Yan , Steinbruchel Christoph
Published: May 2007

A-site deficient perovskite powders are commonly used for high- performance SOFC cathodes. Lanthanum strontium ferrite (LSF) powders, with an average composition of (La1-x'Srx')y'FeO3+d, were fabricated with an average strontium composition of x'=0.4 and an average A-site deficiency range between 0.8<y'<1.0. Samples were initially evaluated using x-ray diffraction with CuKa radiation and observed to be phase pure perovskite powders. However, when evaluated using high-energy synchrotron radiation, substantial amounts of second phases were observed. A hexaferrite phase was observed for A-site deficient compositions. The presence of the second phase substantially changed the determination of the composition of the perovskite phase. The actual A-site deficiency of the perovskite phase was lower than the average value of the bulk powder. A-site deficient LSF phases that were present in as- fabricated powders were metastable, as further heat treatments allowed for complete reaction to produce a two phase mixture of A-site stoichiometric perovskite and hexaferrite phases.
Initial Characterisation of Cerium Doped Neodymium Cuprates for Solid Oxide Fuel Cell Applications
Authors: Cassidy Mark , Irvine John T.
Published: May 2007

Electrically conducting ceramics are of great interest for high temperature applications such as current collectors and contacts in solid oxide fuel cells (SOFCs). This paper presents the initial characterisation of the high temperature electrical properties of cerium doped neodymium copper oxide (Nd2-xCexCuO4+δ) (NCCO) with respect to Ce content, temperature and oxygen partial pressure for possible SOFC applications. Initial results have shown conductivities in air up to 110Scm-1 at 900{degree sign}C and 60Scm-1 at 800{degree sign}C, with the highest conductivity to date at x = 0.20. With reducing pO2 the conductivity initially rises before dropping significantly. Specimens sintered at 950 {degree sign}C exhibited significant improvement in conductivity with time at temperature suggesting continued in-situ microstructural development. NCCO therefore presents itself as a possible candidate for use as a cathode contact material, sintering to a strong, highly conductive layer at stack operating conditions.
Activation Process of Solid Oxide Fuel Cells under Polarization Conditions
Authors: Kikuchi Ryuji , Murakami Kota , Futamura Makoto , Matsui Toshiaki , Eguchi Koichi
Published: May 2007

Power generation characteristics were improved during electrical loading on the cells with Zr-containing electrolyte and La-containing cathode, mainly because of decrease in the resistance of the cathode. On the contrary, the resistance of anode was slightly decreased, and thus the cell activation can be derived from cathode and/or cathode/electrolyte interface. LSM/YSZ/Pt was fabricated and the impedance between LSM and reference electrode was measured. The impedance was reduced by cathodic current treatment for ca. 60 min in air, whereas raised by anodic current treatment. Reversible behavior of the impedance was observed for cathodic and anodic current treatments. In addition, oscillation in cathode potential during current loading was observed depending on the partial pressure of oxygen. From these experimental results, it is inferred that the oscillation behavior and cell activation process can be related to redox of manganese species by current passage in the proximity of the three-phase boundary.
Electrochemical Impedance Studies of SOFC Cathodes
Authors: Hjelm Johan , So̸gaard Martin , Wandel Marie , Menon Mohan , Mogensen Mogens , Hagen Anke
Published: May 2007

Mixed ion- and electron-conducting composite electrodes consisting of doped ceria and perovskite have been studied by electrochemical impedance spectroscopy (EIS) at different temperatures and oxygen partial pressures. This paper aims to describe the different contributions to the polarisation impedance of the cathode at intermediate operating temperatures. The perovskite is of the La-Sr-Co-Fe type. The EIS response of symmetrical cells with a thick (~200 µm) gadolinia doped ceria electrolyte was compared with the impedance contribution of the cathode of a full anode supported cell. The full cells had a Ni-YSZ anode and anode support, a thin YSZ electrolyte, and a CGO barrier layer. The symmetric and full cell cathode responses were compared at open-circuit voltage. Humidified hydrogen was used as the fuel in the full cell measurements. Differential analysis of the impedance data was used to identify frequency ranges where changes occur upon degradation and oxygen partial pressure variations.
Electronic Structure Studies of La1-xSrxCoO3-δ Using High Temperature Magnetization Measurements
Authors: Baskar Dinesh , Adler S.B.
Published: May 2007

High temperature/controlled atmosphere magnetic measurements using a Faraday magnetometer were used to probe the electronic structure of La1- xSrxCoO3-δ (LSC). We find that high temperature magnetic behavior of La1- xSrxCoO3-δ as a function of oxygen nonstoichiometry suggests co-existence of localized and delocalized electronic states. Above 800{degree sign}C oxygen exchange with the gas principally involves delocalized electrons, while at lower temperatures the situation becomes more complex. We discuss this behavior in the context of existing theories of electronic structure, as well as electron transport properties.
Electrode Performance at Hetero-interface of Perovskite-related Oxides, (La, Sr)CoO3-δ / (La, Sr)2CoO4-δ
Authors: Yashiro Keiji , Nakamura Takashi , Sase Maya , Hermes Florian , Sato Kazuhisa , Kawada Tatsuya , Mizusaki Junichiro
Published: May 2007

The hetero-interface electrode, LaSrCoO4-d on La0.6Sr0.4CoO3-d, was examined by means of impedance analysis and steady state polarization method. The performance of the hetero-interface electrode was higher than those of LaSrCoO4-dγandγLa0.6Sr0.4CoO3-d. This is attributed to the enhancement of oxygen exchange at the hetero interface of LaSrCoO4-dγandγLa0.6Sr0.4CoO3-d.
Performance of Ag/La0.6Sr0.4Co1-xFexO3 (x = 0 - 0.8) Nanotube Composite Cathodes for IT-SOFCs
Authors: Bellino Martín G. , Sacanell Joaquín G. , Lamas Diego G. , Leyva Ana G. , Walsöe de Reca Noemí E.
Published: May 2007

We investigated the performance of Ag/La0.6Sr0.4Co1-xFexO3 (x = 0;0.8) nanotube composite cathodes using samaria-doped ceria as electrolyte. These composites were prepared by mixing a commercial Ag paste and La0.6Sr0.4Co1-xFexO3 (x = 0;0.8) nanotubes synthesized by the pore wetting technique using plastic templates. Electrochemical impedance spectroscopy analyses showed that the incorporation of La0.6Sr0.4Co1-xFexO3 nanotubes significantly enhances the performance of the cathode in comparison to pure Ag due to their high specific surface area.
Ag Thin Film Cathode for LSGM Electrolyte LT-SOFCs
Authors: Sasaki Kazuya , Muranaka Minoru , Suzuki Akihiro , Terai Masayuki
Published: May 2007

A composite Ag-La0.6Sr0.4Ga0.8Mg0.2O3 (LSGM) thin film cathode was synthesized on the LSGM electrolyte successfully by a simultaneous RF sputtering method of Ag and LSGM. The microstructure of the thin composite film cathode was examined by FE-SEM and EDX. Nano-size LSGM particles existed in the grain boundary of the Ag thin film, and prevented the agglomeration of Ag. As the result, the crystal grain of the Ag thin film cathode became small, and although it was a thin film, it had high thermal stability. The coexistence of Ag and LSGM was investigated by FE-SEM, and EDX. The initial performance and durability of the composite Ag-LSGM thin film as LT-SOFCs cathode operated at 500 to 600 oC were studied by the three-probe AC-impedance method.
Electrophoretically Coated Wire Meshes as Current Collectors for Solid Oxide Fuel Cell
Authors: Itagaki Yoshiteru , Matsubara Fumiya , Asamoto Makiko , Yamaura Hiroyuki , Yahiro Hidenori , Sadaoka Yoshihiko
Published: May 2007

Metal wire meshes were coated with La0.8Sr0.2MnO3 and NiO/YSZ by electrophoretic deposition technique (EPD) and applied them for surface modified current collectors for a solid oxide fuel cell. The current interrupt analyses for each electrode attached with the wire meshes clearly indicated that coated wire meshes remarkably reduced the cathodic and anodic resistances, especially polarization component, compared to using the uncoated meshes. This enhancement of the electrode performance is due to that EPD coating of the metal meshes increases an effective contact area and/or points between the wire mesh and electrode surface, resulting an increase in three-phase boundary length. A single cell with the EPD coated meshes exhibited higher I-V characteristic compared to that with the uncoated meshes as expected from the result of the electrode resistance measurements.