bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Anode Composition on the Performances of Cathode Supported Micro Channel SOFCs
Authors: Yamaguchi Toshiaki , Shimizu S. , Suzuki Toshio , Fujishiro Yoshinobu , Awano Masanobu
Published: September 2009

The effect of anode composition on the electrochemical performance of cathode-supported micro solid oxide fuel cells (SOFCs) was evaluated using current-voltage and AC impedance measurements. The micro SOFCs were fabricated by the extrusion of a microtubular (La0.8Sr0.2)0.97MnO3 support and subsequent surface coating with a Ce0.9Gd0.1O1.95 (GDC)/Sc2O3-doped ZrO2 bilayer electrolyte and NiO-GDC anode layers. Impedance analysis indicated that 50wt%NiO-50wt%GDC anode has higher electrode activity than 70wt%NiO-30wt%GDC anode. The SOFC with 50wt%NiO generated approximately eight times higher power density than that with 70wt%NiO.
Inherent and Induced Conduction in PSZ Cells with Nanocomposite Electrodes
Authors: Prokhorov Igor
Published: September 2009

Ionic conduction in 3Y-PSZ based cell with nanocomposite Ag/PSZ electrodes was studied using dc transient analysis. Observed tremendous increase in conductivity as compared with conventional electrodes was attributed to huge amount of extra carriers due to highly increased density of triple points.
The Use of Conventional SOFC Electrodes in High Temperature Water Electrolysis Mode: An Electrochemical Study of Ni-Cermet and LSM
Authors: Grondin Dominique , Grunbaum Nicolas , Deseure Jonathan , Ozil Patrick
Published: September 2009

Ni-Cermet and LSM were synthesized and tested respectively as solid oxide electrolyser cathode and anode using three-electrode techniques between 973K and 1173K. YSZ was used as the electrolyte and Pt as the counter electrode. Polarization curves and impedance spectra have been analyzed for different gas compositions. The present results highlight a mechanism changing on Ni-cermet electrode upon gas composition. Oxygen ion oxidation on LSM electrode should be described using a Tafel's law depending on oxygen concentration. Moreover resistance polarization electrode exhibits a same magnitude order for LSM electrode as for Ni-YSZ cermet electrode.
Development of a Methanol SOFC APU Demonstration System
Authors: Rechberger Juergen , Schauperl Richard , Hansen John Bo̸gild , Larsen Peter K.
Published: September 2009

In mid 2007 it was decided to develop a SOFC APU demonstration system in the power range of 7 kWel and fuelled by methanol. Target application of the system should be an APU on board of ships. The main development goals were: • demonstration of fully automated and transient operation • electrical efficiency > 40% • thermally integrated in a gas-tight box • start-up time below 1 hour • project duration 8 months
Degradation in Solid Oxide Fuel Cells Operating with Alternative Fuels
Authors: LaBarbera Mark , Fedkin Mark , Lee Jeoung , Zhow Zoungfei , Lvov Serguei
Published: September 2009

Solid Oxide Fuel Cells (SOFCs) have been shown to generate power with a wide variety of hydrocarbon based fuels. The operation of SOFCs with alternative fuels is hindered by carbon deposition and sulfur poisoning. Here we analyze the performance and degradation of SOFCs with different types of anode, including Ni-YSZ, Cu-ceria, and Rh-ceria based anodes. The tested fuels include Pennsylvania crude oil, JP-7 and JP-8 Plus jet fuels, waste vegetable oil, ethanol, and biodiesel. The performance of the cell with each fuel was characterized with cell voltage vs. current density curves, degradation tests, and electrochemical impedance spectroscopy measurements.
Carbon Deposition and Power Density in Rechargeable Direct Carbon Fuel Cells with Gadolinium-doped Ceria and Scandium-stabilized Zirconia
Authors: Tagawa Yuki , Ohba Fuhito , Takei Chikara , Ihara Manabu
Published: September 2009

Rechargeable Direct Carbon Fuel Cells (RDCFC) with Ni-cermet anodes and oxide anodes were developed. An RDCFC with a Ni/GDC (gadolinium-doped ceria) anode and 0.3-mm-thick ScSZ (scandium-stabilized zirconia) electrolyte with propane as the charging gas for 5 min at 1173 K exhibited a maximum power density of 258 mW/cm2, which is a 5 times improvement over a previously reported similar RDCFC except with YSZ electrolyte.  To investigate the reaction mechanism in RDCFCs and the role of Ni, the power generation of RDCFCs and conventional SOFCs with Ni/GDC, Ni/ScSZ, GDC, and ScSZ/GDC anodes was evaluated.
Preparation and Performance of CuO-GDC Anode Supported Unit Cells for Direct Utilization of Hydrocarbon Fuels
Authors: Lee Jong Jin , Myung Jae-ha , Ko Hyun Jun , Hyun Sang-Hoon
Published: September 2009

The CuO-ceria anodes have been developed for direct utilization of hydrocarbon fuels in SOFCs. The Cu in the anode has a part of an electric conductivity as well as carbon tolerance. On the other hand, because of no catalytic activity of Cu for direct electrochemical oxidation of hydrocarbon fuels, CeO2 materials were used to catalyze the oxidation reaction at the operating temperature range of IT-SOFCs (600 ~ 800 oC). Dense ceria electrolyte was sintered at temperature below 1100 oC using small amounts (about 1 mol%) of transition metal oxide (CuO and Co3O4) additives. Therefore, the CuO-GDC anode supported electrolyte cells could be fabricated via tape-casting and co-firing as the cost-effective process. The CuO-ceria baased anodes showed the maximum power density of 0.11 Wcm-2 and almost no carbon deposition until 500 hours.
Novel Oxidative Fuel Desulfurization System
Authors: Alptekin Gokhan , Jayaraman Ambal , Cook Ron , Dubovik Margarita , Schaefer Matt , Monroe John
Published: September 2009

The major drawback to the use of fuel cells as electric generators and auxiliary power units (APUs) by deployed forces is their inability to directly use battlefield fuels. Fuel Cells require a clean, essentially sulfur-free feed stream to prevent poisoning of the anode catalyst. TDA Research, Inc. (TDA) is developing a novel oxidative fuel desulfurization system, a key component of a compact fuel processor, to produce a sulfur-free feed for fuel cell power generators that run on high sulfur JP-8 fuel. TDA's desulfurization system uses a catalyst to first oxidize the thiophenic sulfur species in the fuel to their respective sulfones using molecular oxygen in air and then to remove the oxidized sulfur compounds with a novel regenerable, mesoporous sorbent to deliver essentially sulfur-free fuel to the fuel processor. The preliminary results from our catalyst and sorbent development efforts are presented here.
Physics of Failure based Damage Modeling for SOFC Development
Authors: Gassner Gert , Langmayr Franz , Prenninger Peter
Published: September 2009

Damage modeling can be used as a highly useful and cost effective tool to support the product development process. Models, referring to physics and chemistry of damage, generate a robust basis for reliability and lifetime assessment. They deliver reliable relationships between load and damage kinetics, which is used to evaluate damage kinetics under various operation conditions and boundaries. Simplified damage models, based on the relationship between operation conditions and damage kinetics can be used already during early phases of product development, when component load data measurements are not yet available. Thus, relevant input for decision making can be generated already within the concept phase. Throughout the development process accuracy rises step-by-step with the quality of available probes and data. This analysis method is in particular useful for decision making in situations with a limited amount of information. This paper describes the physics of failure approach to support SOFC development ranging from concept to validation. It describes the approach and lines out some typical failure modes. Further it describes typical applications to support component layout, test design, validation planning and failure assessment.
Dynamic Electrochemical Model For SOFC-Stacks
Authors: Klotz Dino , Weber André , Ivers-Tiffée Ellen
Published: September 2009

A dynamic electrochemical model based on an equivalent circuit model for anode supported cells (ASC) was developed further to the stack plane level. The model parameters were identified from experimental ASC data (iv-curves and EIS) followed by a pre-identification via the distribution of relaxation times (DRT) and a Complex Nonlinear Least Squares fit (CNLS-fit). The dynamic electrochemical stack model allows to separate the contributions of (i) ohmic resistance, (ii) gas phase polarisation (anode substrate), (iii) electrochemistry in the anode functional layer and (iv) oxygen reduction reaction (cathode) as a function of operating voltage and fuel gas composition along the gas channel. As a conclusion, the stack impedance and the static and dynamic current density distribution can be simulated on a stack plane level for a broad range of operating conditions.
High Volume Fabrication of Ready-to-Stack Components For Planar SOFC concepts
Authors: Venskutonis Andreas , Brandner Marco , Kraussler Wolfgang , Sigl Lorenz
Published: September 2009

Plansee has been active in the development of powder-metallurgical (P/M) interconnects for planar SOFCs since the 1990s. After the proof of feasibility of our dedicated chromium materials technology, we have lately focused on the development of cost-effective and industrially capable routes for the series production of inter¬connects. Net shape P/M fabrication has been introduced as a viable technology for the production of planar interconnects for high temperature SOFC systems. In this context different P/M processing approaches were compared and assessed with respect to their suitability for various SOFC concepts. Customers' needs for high volume production led to the development of a continuous and fully automated manufacturing technology which follows the process scheme of ferrous P/M products for the automotive industry.
Novel Method for Measuring Chromia Evaporation from SOFC Interconnect Materials
Authors: Casteel Micah , Willson Patrick , Goren Tolga , O'Brien Peter , Lewis Daniel
Published: September 2009

One of the major factors limiting solid oxide fuel cell (SOFC) performance is the degradation of chromium containing interconnects during operation. Under SOFC operating conditions chromium ions are vaporized by the cathode gas and reduced at catalytic sites within the cathode to form Chromium (III) Oxide. The formation of Cr2O3 blocks catalytically active sites and results in significant degradation in performance over the life of a fuel cell stack. This degradation has been traditionally measured via the transpiration measurement system; however, this method is expensive and time consuming. A novel method has been proposed to supplement the standard transpiration measurement system utilizing low cost solution conductivity measurement. Conductivity is linearly correlated to the amount of dissolved chromium species in a deionized water (DI water) solution and initial tests indicate that chromium concentration can be continuously monitored as a function of time using the solution conductivity method.
Improvement of Oxidation Resistance of Fe-Cr Ferritic Alloy Sheets for SOFC Interconnects
Authors: Yasuda Nobutaka , Uehara Toshihiro , Okamoto Masayuki , Aoki Chuya , Ohno Takehiro , Toji Akihiro
Published: September 2009

Fe-Cr ferritic alloys are applied for interconnects of solid oxide fuel cells (SOFCs) operated at around medium temperatures. The oxidation behavior of sheets with various thicknesses of Fe-22%Cr ferritic alloy, ZMG232L, was investigated. The oxidation rate of thin sheet was much higher than that of thick one because Cr content decreased under oxide layer of edge part of thin sheet and therefore Cr oxide became unstable and Fe was mainly oxidized. Such accelerated oxidation behavior was able to be improved by reducing Mn, increasing Cr, and adding W.
Long-Term Stability of the LSM-Coated Crofer22APU for Solid Oxide Fuel Cell Interconnect
Authors: Song Rak-Hyun , Pyo Seong-Soo , Lim Tak-Hyung , Lee Seung-Bok , Shin Dong-Ryul
Published: September 2009

We have successfully fabricated a Crofer22APU with (La0.8Sr0.2)0.98MnO3 layer which has good oxidation resistance and long-term stability, as well as to prevent the contamination of cathode due to the chromia rich vaporization. The (LSM) layer was coated on Crofer22APU via a wet spray coating process. The adhesive degree of an interface (LSM layer/Crofer22APU) increased with the surface roughness of Crofer22APU. After the oxidation experiments of the LSM coated Crofer22APU during 8000 hours, the ASR showed a low value of 23 mΩ⋅cm2. These result have shown that the coated oxides layer prevents the formation and the growth of scale (Cr2O3 and (Mn, Cr, Fe)3O4 layer) and enhances the long-term stability for SOFC.
High Temperature Glass-ceramic Seals for SOFC Applications
Authors: Liu Chien-Kuo , Yung Tung-Yuan , Lin Kin-Fu , Lee Ruey-Yi , Wu Szu-Han
Published: September 2009

A novel borosilicate glass, gc9, with the main compositions of BaO-Al2O3-B2O3-SiO2 and other minor additives, has been developed by INER as a high temperature seals for solid oxide fuel cell (SOFC) stacks. The glass transition temperature (Tg) and softening temperature (Ts) of gc9 glass are 652ºC and 745ºC, respectively. Its average coefficient of thermal expansion (CTE) is about 11.0 ppm/ºC (RT~800ºC), which is compatible with that of interconnect and MEA of a SOFC stack. Additionally, a proper balance of sealant properties, such as its viscosity and shrinkage behavior at different temperatures, is essential to have a successful sealing for a SOFC stack. The viscosity evolution and shrinkage amount of a gc9 glass powder pellet at elevated temperatures were measured using a high temperature parallel plate viscometer. Under an external loading of 0.080 MPa, the minimum viscosity, viscosity reflection point, and shrinkage percentage are 108 Pa•s, 806ºC, and 64%, respectively.
Gas Sealing Reliability of Glass/Ceramic Composite Seals under SOFC Working Conditions
Authors: Suda Seiichi , Kawahara Koichi , Jono Kaori , Mizuta Yasutoshi
Published: September 2009

Gas-tight seals are also indispensable for fabricating high-performance portable SOFC as well as other cell components because gas sealing leakage causes severe damage to integrated cells or stacks. We investigated glass/ceramic composite materials to apply to gas-tight seals for portable SOFC. The composite seals with glass precursor particles and ceramic precursor showed relatively high reliable gas sealing properties under some SOFC working conditions. The composite seals showed sufficient high gas sealing properties in humidified hydrogen gas as well as air, and humidified hydrogen gas would be little impact on fusible conditions. The seals can be used in hydrogen as well as air. The composites also exhibited high durability against the thermal cycle between 650oC and 250oC, and they kept gas-tight sealing and no leakage was observed under raid heating conditions at the rate more than 200oC/min.
Redox Properties of Ordered Macroporous Ce-Zr Mixed Oxides
Authors: Tonti Dino , Torralvo Maria Jose , Enciso Eduardo , Martinez Lidia , Roman Elisa , Sanz Jesus
Published: September 2009

In this contribution finely textured three-dimensionally ordered macroporous (3DOM) mixed oxides of composition Zr0.6Ce0.4O2 were prepared by the inverse opal technique. By using thermal analysis and photoelectron spectroscopy the oxygen storage and the redox response to different environments has been investigated. Multiple high temperature oxidation-reduction cycles decrease the initial high sensitivity of the surface oxidation state of Ce to the environment. This has been ascribed to the development of Ce(III) phases. Finally, we present a simple analysis of XPS data that allow the detection of surface inhomogeneities on Ce-containing oxides. We show that phase segregation can produce chemically heterogeneous surfaces.
Possible Suppression of Partial Electronic Conductivity by Electron Traps in CeO2-based Electrolytes by Electron Traps
Authors: Yoo Han-Ill , Park Sang-Hyun , Chun Jakyu
Published: September 2009

A critical drawback of ceria-based electrolytes is that they are much more prone to reduction, thus limiting the lower bound of their electrolytic domain to much higher an oxygen activity than the classic electrolyte YSZ. We examined the possibility to suppress the partial electronic conductivity, thus to expand the electrolytic domain width, of acceptor(A)-doped Ce1-xAxO2-x/2 by trapping reduction-induced electrons by variable valence impurities with 3d (Ti, Mn, Fe, Co, Cu) and 4f electrons (Eu, Yb, Sm, Tb). It has been found that a few of 4f elements are indeed effective to extend the domain width to lower oxygen activity by as much as two orders of magnitude. We will report the result together with the inner working of suppressing the partial electronic conductivity of Ce1-xAxO2-x/2.
Role of Lattice Strain and Defect Chemistry on the Oxygen Vacancy Migration at the (8.3% Y2O3-ZrO2) / SrTiO3 Hetero-Interface: A First Principles Study
Authors: Kushima Akihiro , Yildiz Bilge
Published: September 2009

We report on the mechanism and the upper limits in the increase of oxygen ion conductivity at oxide hetero-interfaces, particularly the 8.3%Y2O3-ZrO2/SrTiO3 (YSZ/STO) as a model interface. We consider two factors contributing to the increase in ionic conductivity at or near the interface: 1) a favorable strain state to shift and/or change the symmetry of electron energy levels to provide improved charge transfer and mobility. 2) the alteration of the defect chemistry to enhance the density and distribution of oxygen vacancies. First principles and Kinetic Monte-Carlo simulations were performed to identify the atomic-scale nature of the hetero-interface and the oxygen vacancy migration barriers and diffusivity. Our results suggest that the modulation in both the lattice strain and the defect chemistry due to the YSZ/STO interface can enhance the ionic conductivity in YSZ up to six orders of magnitude by reducing the migration barrier and increasing the oxygen vacancy concentration, respectively.
Structural Stability of GDC Electrolyte for Low-Temperature SOFCs Depending on Fuels
Authors: Ko Hyun Jun , Lee Jong Jin , Hyun Sang-Hoon
Published: September 2009

It has been considered to apply GDC (Gd0.1Ce0.9O1-X) to low-temperature SOFC electrolytes at a low temperature. However, ceria cannot be efficiently used with hydrogen and wet hydrocarbon fuels because its structure change (Ce+4→Ce+3) causes a decline of mechanical strength under a reduction atmosphere. In this work, the structural stability test of the GDC electrolyte for low-temperature SOFCs was investigated under reduction and oxidation atmospheres depending on the fuels. Each structural stability test was examined under reduction (H2) and oxidation (dry CH4) atmospheres at 650 °. Micro-cracks and pinholes were observed on the electrolyte surface and at the fracture after completing the test with hydrogen fuel, but in the case of dry methane, only small amounts of defects were found at the fracture. This study clearly confirmed from the XPS data that many more Ce+4 ions transform into Ce+3 ions under the reduction (H2) atmosphere (1, 2).
Low Sintering Temperature and Electrical Properties of Samarium-Doped Ceria
Authors: Camilo de Souza Eduardo Caetano , Muccillo Eliana N.
Published: September 2009

Ce0.8Sm0.2O1.95 solid electrolytes were synthesized by a modified homogeneous precipitation method aiming optimizing their densification behavior and electrical conductivity. Nanoparticles with 3 to 8 nm in diameter were obtained after calcination at 450 and 700ºC, respectively. The linear shrinkage of powder compacts shows an endset temperature around 1200ºC with maximum shrinkage rate at 1000ºC. High relative density values (~ 93%) were obtained for pellets prepared from mixed solvents at only 1150ºC. The electrical conductivity of both grains and grain boundaries exhibits a considerable dependence on the type of alcohol used as solvent and on the residual porosity.
Investigation of High Temperature Elastic Modulus and Internal Friction of SOFC Electrolytes Using Resonance Method
Authors: Kushi Takuto , Sato Kazuhisa , Unemoto Atsushi , Amezawa Koji , Kawada Tatsuya
Published: September 2009

The Young's modulus, the shear modulus, the Poisson ratio and the internal friction of typical electrolyte materials for SOFC, (Gd2O3)0.05(CeO2)0.9, (Sm2O3)0.05(CeO2)0.9, (Y2O3)0.08(ZrO2)0.92, (Y2O3)0.1(ZrO2)0.9, (Sc2O3)0.1(ZrO2)0.9, (Sc2O3)0.9Ce0.01(ZrO2)0.89 were evaluated by a resonance method. The measurements were carried out from room temperature to 1273 K in flowing pure Ar. The Young's modulus of (Gd2O3)0.05(CeO2)0.9 and (Sm2O3)0.05(CeO2)0.9 gradually decreased with increasing temperature as expected for the typical ceramics. However, the Young's modulus of the series of zirconia drastically decreased in the temperature range between 573 K and 873 K, and correspondingly the internal friction increased. Such a characteristic temperature dependence of the mechanical properties was discussed in terms of phase change.
Zirconia EB-PVD Electrolyte Films: Structure, Mechanical Properties and Conductivity
Authors: Vasylyev Oleksandr D. , Smirnova Alevtina , Brychevskyi Mykola , Pryshchepa Ievgenii , Dubykivskyi Leonid , Sameluk Anatolii , Vereschak Viktor , Malzbender Juergen
Published: September 2009

Structure, elastic modulus and conductivity of EB-PVD 10Sc1CeSZ films deposited on NiO-8YSZ anodes were studied. The films have laminar-columnar structure nucleating as bundles of columns of nano-sized diameter. Two types of lamella could be distinguished with a thickness range of 0.5 - 5.0 μm and 0.1 - 0.2 μm, respectively. This structural anisotropy is associated with the distribution of chemical elements across the as-deposited film (Zr, Sc, Ce) and diffusion from the anode (Ni, Y), which most likely is a consequence of instabilities of the deposition process and the condensation mechanism. The elastic modulus of the film is also anisotropic; showing values of 120 GPa at the surface and 105 GPa in the cross-section. Annealing in air increases the elastic modulus up to 140 GPa. The area near the interface with the anode has a higher modulus than that near the surface, which might be associated with the solidification process of the film. The conductivity of the EB-PVD film is half an order of magnitude higher than for a film deposited by screen printing one.
Characterization of Co-doped LSGM Electrolyte Prepared by GNP for IT-SOFC
Authors: Lee Dokyol , Han Ju-Hyeong
Published: September 2009

Co doping was used to enhance electrical conductivity of La0.8Sr0.2Ga0.8Mg0.2O2.8. The La0.8Sr0.2Ga0.8Mg0.2-xCoxO2.8 powders of two different compositions (x = 0.05 or 0.1) were synthesized using glycine nitrate process as the electrolyte material of intermediate temperature solid oxide fuel cells (IT-SOFCs). The electrical conductivity of La0.8Sr0.2Ga0.8Mg0.1Co0.1O2.8 at 800° is observed to be 0.145S/cm which is higher than that of La0.8Sr0.2Ga0.8Mg0.2O2.8 (0.127S/cm). And the linear thermal expansion coefficient was measured to be 15.2×10-6K−1 for La0.8Sr0.2Ga0.8Mg0.1Co0.1O2.8 which is very close to that of La0.6Sr0.4Co0.2Fe0.8O3-x (13.4×10-6K−1). The phase stability of La0.8Sr0.2Ga0.8Mg0.1Co0.1O2.8 in contact with La0.6Sr0.4Co0.2Fe0.8O3-x was fairly good. And the relative density values of La0.8Sr0.2Ga0.8Mg0.1Co0.1O2.8, when sintered at 1400° for 4 hours, were over 98%.
Exploring Highly Yttrium Doped Barium Zirconate Proton Conductor Electrolytes for Application in Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFCs)
Authors: Fabbri Emiliana , Pergolesi Daniele , Licoccia Silvia , Traversa Enrico
Published: September 2009

High temperature proton conductor (HTCP) perovskites are gaining growing attention as electrolyte materials for application in intermediate temperature solid oxide fuel cells (IT-SOFCs). In particular, Y-doped barium zirconate (BZY) electrolyte has been recently the subject of several studies because of its good chemical stability. To investigate the influence of Y concentration on the electrical properties of BZY, BaZr1-xYxO3-δ (0.3 {less than or equal to} x {less than or equal to} 0.6) oxides were synthesized using a wet chemistry process to obtain powders with controlled compositional homogeneity and purity at low processing temperatures. The synthesized powders were characterized by X-ray diffraction (XRD) and inductively coupled plasma (ICP) analysis. Dense electrolytes were obtained pressing the calcined powders into cylindrical pellets and then sintering at 1600 {degree sign}C for 12 h. Electrical conductivity of the sintered pellets was measured as a function of the temperature and the Y concentration by electrochemical impedance spectroscopy (EIS) measurements.
Fabrication and Generation of Intermediate Temperature Operating SOFC based on Y-doped BaZrO3 Proton Conducting Oxides
Authors: Iguchi Fumitada , Nagai Masahumi , Sata Noriko , Yugami Hiroo
Published: September 2009

An electrolyte supported type intermediate temperature operating SOFC (IT-SOFC) using 15mol% Y-doped BaZrO3 (BZY15) is fabricated and tested in the temperature range of 650oC to 550oC to study fundamental properties of an IT-SOFC using proton conductors. The measurement of I-V characteristics and impedance spectra reveal that BZY15 is superior to oxygen ionic conductors as an electrolyte material from the viewpoint of electrolyte resistance in the tested temperature range. The results also confirm the necessity of reducing cathodic overpotential.
BITX: New Electrolyte for Oxide Ion and Proton SOFC
Authors: Noirault Samuel , Quarez Eric , Caldes Maria Teresa , Le Gal La Salle Annie , Joubert Olivier
Published: September 2009

Ba2In2(1-x)Ti2xO5+x•1-x compounds (BITx) have been prepared by solid state reaction. Whereas Ba2In2O5 corresponds to an ordered Brownmillerite structure, for 0.15 < x < 1 all members adopt a disordered cubic perovskite structure at RT. This phase transformation induces a drastic increase of the anionic conductivity level. At 700{degree sign}C, 10-2 S.cm-1 is obtained for BIT07. Stable under hydrogen, the x = 0.7 was selected and a SOFC built on BIT07 and Ni/BIT07 cermet was tested. The peak power is about 500mW at 800{degree sign}C. Due to the basicity of these compounds, water uptake of BITx was investigated. The change of the lattice volume upon hydration, inferred from X-ray diffraction data, appears as an important parameter for the characterization of perovskite-type proton conductors. Proton conductivity higher than 1 mS.cm-1 was measured at 400{degree sign}C for BIT02. A ceramic fuel cell based on this material as electrolyte was evaluated.
Effect of Gun Current of APS on Microstructure of Apatite-type Lanthanum Silicate (ATLS) Electrolyte Coatings
Authors: Gao Wei , Lapostolle Frédéric , Liao Hanlin , Coddet Christian
Published: September 2009

The microstructure of apatite-type lanthanum silicate (ATLS) electrolyte coatings was studied by the effects of the plasma-sprayed process parameters. This work demonstrated experimentally that the use of as-calcinated feedstock powders is sufficient to obtain the dense La10(SiO4)6O3 electrolyte coatings by atmospheric plasma spraying (APS) with an unusual broad range of gun currents.
Quantification of Ni-YSZ Anode Microstructure Based on Dual Beam FIB-SEM Technique
Authors: Iwai Hiroshi , Shikazono Naoki , Matsui Toshiaki , Teshima Hisanori , Kishimoto Masashi , Kishida Ryo , Hayashi Daisuke , Matsuzaki Katsuhisa , Kanno Daisuke , Saito Motohiro , Muroyama Hiroki , Eguchi Koichi , Kasagi Nobuhide , Yoshida Hideo
Published: September 2009

Three-dimensional microstructure of a conventional Ni-8YSZ anode is quantified by means of dual beam FIB-SEM system equipped with EDX. The microstructure of the anode is virtually reconstructed in a computational field using a series of two-dimensional SEM images acquired. Three-phase-boundary (TPB) density and tortuosity factors are carefully evaluated applying two different evaluation methods to each parameter. TPB density is evaluated by volume expansion method and centroid method, while tortuosity factor is evaluated by Lattice Boltzmann Method calculation and by random walk approach. The estimations of each parameter by two methods match well each other showing the reliability of analyzing methods proposed in this study.
Three-Dimensional Numerical Simulation of Ni-YSZ Anode Polarization Using Reconstructed Microstructure from FIB-SEM Images
Authors: Matsuzaki Katsuhisa , Kanno Daisuke , Teshima Hisanori , Shikazono Naoki , Kasagi Nobuhide
Published: September 2009

The overpotential in a three-dimensional Ni-YSZ anode model structure obtained by a dual-beam focused ion beam-scanning electron microscope is predicted by lattice Boltzmann method. Gaseous, ionic and electronic transport equations with electrochemical reaction at the three-phase boundary are solved with an assumption of local equilibrium in the solid oxide. The gas transport is modeled by a so-called dusty gas model. The numerical simulation is performed under the current density conditions of 0.01, 0.1, 0.3 and 0.7 A/cm2. Three-dimensional electrochemical potential distributions inside a test anode microstructure are presented. The proposed method can be used for predicting SOFC electrode polarization.
Theoretical Study for Properties of SOFC Anode Using Three-Dimensional Porous Structure Simulator
Authors: Ogura Teppei , Ishimoto Takayoshi , Nagumo Ryo , Koyama Michihisa
Published: September 2009

Anodic microstructure influences overpotential characteristics and the optimization of the microstructure for given anode materials and operating conditions is challenging. In this study, we have tested enormous number of microstructures of Ni-YSZ cermet anode using the porous structure simulator developed previously. As a result of overpotential calculations, we found anode structure giving superior overpotential characteristics with different microstructures. Further, our analyses clarified that consideration of only triple-phase boundary length is not enough to explain the overpotential dependence on microstructures. We therefore introduced a new index to relate overpotential characteristics with porous microstructures by taking into account both triple-phase boundary length and its spatial distribution.
3-dimensionally Ordered Macroporous Ni-YSZ for Low Temperature SOFC
Authors: Munakata Hirokazu , Otani Masashi , Katsuki Yuki , Kanamura Kiyoshi
Published: September 2009

Ni-YSZ anode with three-dimensionally ordered macroporous (3DOM) structure was applied to solid oxide fuel cell, in order to demonstrate high potential of 3DOM structure for electrodes of intermediate temperature solid oxide fuel cells (IT-SOFCs). Polystyrene beads with particle size of 2.5 μm or 1.4 μm were used as the template for 3DOM Ni-YSZ. The cell with LSM-YSZ / YSZ / 3DOM Ni-YSZ configuration showed better performance than that of the conventional cell with random-structured Ni-YSZ. The polarization resistance of Ni-YSZ anode was further reduced due to 3DOM structure with the smaller pores that provided large electrochemical interface. Consequently, 374 mW cm-2 and 119 mW cm-2 were obtained as the maximum power density at 700 {degree sign}C and 600 {degree sign}C, respectively.
Determination of the Anode Flow Distribution in a SOFC Stack at Nominal Operating Conditions by EIS
Authors: Dekker Nico , Van Wees J. F. , Rietveld B. G.
Published: September 2009

The maximum efficiency of a fuel cell stack is to a large extent determined by the maximum applicable fuel utilization. To achieve a high fuel utilization an even flow distribution of the fuel gas over the cells in the stack is required. The flow distribution is determined by many factors, such as the design of the stack, production tolerances and changes of the fuel flow fields during operation by creep and corrosion. For the determination of the fuel flow distribution within the stack, an in-situ method was developed based on Electrochemical Impedance Spectroscopy (EIS). By this method the fuel flow distribution over the cells can be measured at the nominal operating condition, providing insight in the flow distribution in time without disturbing the long term behavior. The results of the method will be shown by measurements with a Staxera Mk-100 stack, consisting of 30 cells
H2-H2O Effective Binary Diffusivity Measurement in Solid Oxide Fuel Cell Anode Using an Electrochemical Cell
Authors: He Weidong , Yoon Kyung Joong , Eriksen Ryan S. , Gopalan Srikanth , Basu Soumendra N. , Pal Uday B.
Published: September 2009

The effective binary diffusivity of H2 and H2O in a Ni and yittria-stabilized zirconia (YSZ) anode of the solid oxide fuel cells (SOFCs) was measured between 650 and 800oC using an electrochemical cell consisting of an oxygen pump, an oxygen sensor, and a porous SOFC anode pellet. The effective binary diffusivity was obtained from the relationship between the current density across the oxygen pump, and the H2 partial pressure gradient across the anode sample measured using the oxygen sensor. The anode limiting current density and concentration polarization were estimated using the experimental results.
Strong Metal Support Interactions of Infiltrated Ni with TiO2 in a Porous YSZ Anode Matrix - A Possible Method for Ni-Stabilization
Authors: Singh C. Anand , Bansal Loveleena , Tiwari Pankaj , Krishnan Venkatesan V.
Published: September 2009

In earlier research, sintering of Ni infiltrated into porous anodes in SOFCs was responsible for loss in performance. The idea of introducing strong metal support interactions (SMSI) has been investigated as a possible method for curbing the sintering of Ni. Titania, when used as a support in catalysts, has been found to show SMSI behavior with metals, dispersed on its surface. Porous anodes, typically used as the SOFC support (anode supported cells), containing titania and Ni have been prepared using impregnation methods and characterized using Chemisorption, Scanning Electron Microscopy (SEM) and XRD studies. SEM results do indicate strong wetting of nickel particles with titania after reduction at 800åC and reduced amount of sintering on prolonged exposures in hydrogen at high temperature. Hydrogen chemisorption studies also revealed a sharp drop in Ni dispersion from 5.3% to less than 1%, due to the presence of titania, at 800oC confirming SMSI effects in Ni-TiO2-YSZ systems.
Operation of Ni-YSZ Anode Supported Solid Oxide Fuel Cell on Different Simulated Syngas
Authors: Chen Tao , Li Tingshuai , Miao He , Wang Wei Guo , Wu Yanan
Published: September 2009

Ni-YSZ anode supported solid oxide fuel cells (ASCs) were tested under various simulated syngas. There was no voltage degradation of the cell operated on 41%H2-7%CH4-6%CO-11%CO2-35%H2O fuel condition for nearly 450 hours. However, the high vapor content reduced the open circuit voltage (OCV) and discharge voltage. The cells run steadily with most dry syngas until the simulated reforming temperature reduced to 500oC and steam to carbon ratio (S/C) reduced to 3. The corresponding composition of this syngas was 49%H2-24%CH4-8CO -14CO2-5%H2O. In this case, the voltage dropped quickly and the cell failed within 5 hours. The microstructure analysis showed that the failed cell had a carbon deposit layer of approximately 10μm thickness closed to the anode surface. The results indicated that carbon deposited quickly on Ni surface when there was no adequate carbon dioxide or vapor to avoid methane cracking.
Electrochemical Analysis on Degradation of Ni-GDC Cermet Anode for SOFC
Authors: Watanabe Hidetaka , Unemoto Atsushi , Amezawa Koji , Kawada Tatsuya
Published: September 2009

AC impedance measurements were carried out with Ni-GDC cermet anode in various partial pressures of hydrogen at temperatures from 873 K to 1273, the data was analyzed focusing on the chemical capacitance. It was proposed that the effective reaction zone (ERZ) of the cermet anode could be evaluated by comparing the observed capacitance and the one expected for the whole electrode. The ERZ was estimated as 1 μm for the Ni-GDC electrode investigated in this work. Degradation mode of the cermet anode was discussed based on the observed change in the ERZ. It was suggested the agglomeration of Ni particles might be the main factor for the degradation during the thermal cycle at high temperature.
The Role of Interstitial Hydrogen Species in Ni/YSZ Patterned Anodes: A 2D Modeling Study
Authors: Vogler Marcel , Bessler Wolfgang G.
Published: September 2009

The mechanistic details of the hydrogen oxidation at Ni/YSZ anodes are subject of controversial discussion. In the light of potential accumulation of secondary phases at the three-phase boundary, a mechanism involving interstitial hydrogen species in the bulk phases and charge-transfer at the Ni/YSZ two-phase boundary has been proposed. We present a quantitative analysis of this mechanism based on a two-dimensional elementary kinetic model of electrochemistry and bulk diffusion. The use of literature diffusion coefficients yields diffusion-limited current densities that are below those observed in experiments. Assuming increased diffusivity allows to quantitatively reproduce published experimental pattern anode data, including their dependence on gas composition and temperature. This shows the feasibility of interstitial mechanisms when impurities are present and explains their decreased performance. For clean three-phase boundaries, surface spillover pathways are preferred.
Degradation Effects of Ni Patterned Anodes in H2/H2O Atmosphere
Authors: Utz Annika , Störmer Heike , Leonide André , Weber André , Ivers-Tiffée Ellen
Published: September 2009

Patterned Ni anodes on Y2O3-stabilized ZrO2 (YSZ) represent a promising approach to determine the kinetics of electrochemical reactions in SOFC. Contrary to technical Ni/YSZ cermet anodes, the reaction zone for the hydrogen oxidation has the potential to be well defined. In this study the focus was on the structural stability of the Ni patterned anodes and its correlation with activation and degradation processes. Considerable activation and degradation processes with time constants in the order of some hours were found and are discussed: (i) an initial decrease in LSR during the first 20 - 25 h of temperature exposure, attributed to a restructuring process in the Ni thin film (ii) reversible changes in LSR upon pH2O / pH2 variations in correlation to the initial gas composition (iii) rapid reversible changes in LSR upon anodic and cathodic polarization followed by a slow relaxation.
Performance Deterioration of Ni-based Cermet Induced by Electrochemically-generated Steam in Anode
Authors: Matsui Toshiaki , Kishida Ryo , Kim Jin-young , Muroyama Hiroki , Eguchi Koichi
Published: September 2009

Nickel-yttria stabilized zirconia (Ni-YSZ) cermet is a conventional anode for use in solid oxide fuel cells, and its composition and microstructure are carefully controlled to achieve high performance and long-term stability. In this study, the performance stability of electrolyte-supported cell (Ni-YSZ | YSZ | LSM) was examined at 1000ºC by feeding humidified fuel, x% H2O-(100-x)% H2. The influence of cermet composition on deterioration was also studied. The deterioration behavior was significantly dependent on the fuel humidity and cermet composition. In the case of Ni-YSZ with a volumetric ratio of 50 to 50, peculiar phenomena were observed. When the fuel of 30% H2O-70% H2 was supplied to anode and the terminal voltage was fixed at 0.7 V, the current density decreased gradually soon after the discharge up to 70 h. Then a sudden drop in current density occurred. After the subsequent open-circuit holding, the performance was partially recovered in discharge operation. This behavior of deterioration-recovery was reversibly repeated upon discharge-open-circuit holding operation.
Chemical Degradation and Poisoning Mechanism of Cermet Anodes in Solid Oxide Fuel Cells
Authors: Haga Kengo , Shiratori Yusuke , Ito Kohei , Sasaki Kazunari
Published: September 2009

This paper reports the chemical degradation of Ni-based SOFC anodes caused by small amounts of impurities supplied with fuels. In particular, the impurity dependence of degradation behaviors as well as poisoning mechanisms are highlighted and investigated. Poisoning effects by chlorine and siloxanes are found to be critical to achieve satisfactory SOFC durability. In addition, it has also been demonstrated that phosphorus and boron compounds led to gradual decrease in cell voltage, Ni grain growth, and even formation of nickel phosphates. The measured trends are discussed in relation to the thermochemical calculations and FESEM/STEM-EDX analysis.
Ostwald Ripening and Oxidation Kinetics of Nickel Gadolinia Doped Ceria Anodes
Authors: Galinski Henning , Reuteler Joakim , Rupp Jennifer L. , Bieberle-Hutter Anja , Gauckler Ludwig J.
Published: September 2009

The Ostwald ripening and the oxidation of a nickel gadolinia doped ceria (CGO) cermet with an approximate median porosity of 50 volume percent has been studied via focused ion beam (FIB) nanotomography and in-situ X-ray diffraction in the temperature range 773-1323 K. Ostwald ripening has been identified as physical process that promotes degradation of Ni/CGO cermets. The oxidation kinetics is found to be a thermally activated process with an apparent activation energy of 1.7(2) eV at temperatures below 1023 K.
Development of La-doped Ni-SDC Anode for High Performance IT-SOFC of Ni-SDC/LSGM/SSC
Authors: Kawahara Koichi , Suda Seiichi , Kawano Mitsunobu , Yoshida Hiroyuki , Inagaki Toru
Published: September 2009

Sr and Mg co-doped lanthanum gallate electrolyte (LSGM) shows high oxide ion conductivity at temperatures of 650-800oC. However, LSGM has rather high chemical reactivity with anode materials; reaction compounds at the anode/electrolyte would lead to the degradation of the SOFC performance. In order to develop the optimum cermet anode for LSGM, La and Sm co-doped ceria (SLDC) was synthesized and investigated in connection with reactivity between SLDC and LSGM. The NiO-SLDC composite particles synthesized by spray pyrolysis were applied for cermet anodes in order to prevent the anode/electrolyte interface from undesirable interfacial reaction. The power density of the cells with Ni-SLDC anode was found to be higher than that with Ni-SDC anode. Current interruption measurements revealed that La addition to SDC has an effect of the decrease in ohmic loss.
Effect of Operation Conditions on Soot Formation in SOFC Stacks
Authors: Kavurucu Schubert Sena , Kusnezoff Mihails
Published: September 2009

SOFCs can be operated with various fuel types which make them attractive to use for different applications. In many of these applications carbon containing gases are used as fuel that can cause soot formation in the cells especially during heating up - cooling down the SOFC stacks. Experiments have been performed in order to understand the effect of temperature, heating rate and gas composition for carbon containing fuel gas by simulating stack operation parameters. The soot formation phenomenon is studied on the pellets made from anode powders as well as on SOFC one cell stacks. The electrochemical behaviour evaluated by I-V-characteristics and impedance spectroscopy and microscopic analysis of the cells confirm soot formation when SOFC stack is fuelled under unfavourable temperature regions and heating rates. However, it is also found that stack can regenerate itself during operation after a small amount of coke has been deposited on the electrode.
Mitigation of Carbon Deposits Formation in IT-SOFCs Fed with Dry Methane by Anode Doping with Barium
Authors: Aricò Antonino Salvatore , La Rosa Daniela , Lo Faro Massimiliano , Minutoli Maurizio , Monforte Giuseppe , Antonucci Vincenzo , Sin A.
Published: September 2009

The effect of barium-doping on carbon deposition during the CH4 oxidation over a Ni0.53Cu0.47 alloy/CGO cermet catalyst has been investigated in an Intermediate Temperature Solid Oxide Fuel Cell (IT-SOFC). Electrolyte-supported SOFCs composed of different anodes were compared in terms of performance, steady state operation, and formation of carbon deposits on the anode surface. After proper cell conditioning, similar maximum power densities of 285 mW cm-2 and 310 mW cm-2 were obtained in dry methane fuel at 750{degree sign}C for the anodic compositions with and without barium, respectively. As evidenced by microscopy and X-ray diffraction, the anode without barium showed the presence of carbon deposits whereas the anode containing barium did not show significant carbon deposits after a 200 h time-study in dry methane.
Correlation between Crystalline Phase of ScSZ and Carbon Deposition Behavior Over Ni-ScSZ Anode for Internal Reforming of Solid Oxide Fuel Cells
Authors: Matsui Toshiaki , Iida Tatsuya , Kikuchi Ryuji , Kawano Mitsunobu , Inagaki Toru , Muroyama Hiroki , Eguchi Koichi
Published: September 2009

The influence of preparation condition of Ni-ScSZ (scandia-stabilized zirconia) cermet on the tolerance to carbon deposition was investigated in the wide temperature range of 800-1000ºC. The mixture of NiO-ScSZ was subjected to pre-heat treatments prior to use as a cermet electrode. Although the inhibitory effect of ScSZ in Ni-based cermet for carbon deposition is well-known, the present study revealed that the preparation method and firing condition affected the carbon deposition behavior. The Ni-ScSZ cermet obtained from the oxide mixture heated at 1400ºC showed peculiar behavior to carbon deposition. The initial carbon deposition rate at 800-900ºC for this sample was larger than that at 1000ºC, whereas other samples exhibited a reduction in deposition rate with decreasing temperature. The cubic phase stabilization in ScSZ was confirmed for the sample treated at 1400ºC, though ScSZ was in the rhombohedral phase before the heat-treatment with NiO. These results suggested that a strong interaction between NiO and ScSZ was induced by the high-temperature heat-treatment.
Effect of Coal Syngas Fuel Composition on the Performance and Stability of Oxide Anodes
Authors: Bierschenk David M. , Haag Jacob M. , Poeppelmeier Kenneth R. , Barnett Scott A.
Published: September 2009

The performance and stability of La0.8Sr0.2Cr0.82Ru0.18O3-δ (LSCrRu)-Gd0.1Ce0.9O2(GDC) and LaSr2Fe2CrO9-δ(LSCrFe)-GDC composite solid oxide fuel cell (SOFC) anodes were evaluated during SOFC operation on surrogate coal-derived syngas and CO-H2 mixtures. The LSCrRu-GDC cells exhibited the least coking and best performance stability in syngas compositions expected to cause coking, although the LSCrFe-GDC anodes were significantly better than Ni-YSZ. No degradation and minimal coking was observed in LSCrRu-GDC cells during operation on coal gas or pure CO at 700 - 800ºC. All anodes tested showed higher anode polarization resistance (RP,A) in pure CO compared to H2 fuel; the LSCrFe-GDC anode showed lower RP,A in pure CO than the LSCrRu-GDC anode. In coal gas, on the other hand, the LSCrRu-GDC anode showed an RP,A value comparable to that of LSCrFe-GDC. This was explained by the production of H2 at the LSCrRu-GDC anode, due to the significant activity for the water gas shift reaction.
Influence of Some Inorganic Impurities on the Electrochemical Properties and Microstructure of Ni-CGO Anode in Artificial Woodgas Atmosphere
Authors: Nurk Gunnar , Kubacki Adam , Holzer Lorenz , Figi Renato , Graule Thomas , Holtappels Peter
Published: September 2009

The influence of inorganic impurities on the SOFC anode behavior is one of the key issues that have to be solved for developing a SOFC system fuelled with gasified biomass. In this paper the results of initial electrochemical tests of Ni-CGO anodes under load in N2/H2/H2O gas mixtures and in the presence of KCl salt as an inorganic impurity are presented. The Ni-CGO anodes were studied in different conditions: in low concentration potassium chloride vapors (approx. 6 ppm) similar to potassium concentrations in woodgas, very high concentration KCl vapors (approx. 3500 ppm) and after impregnation with KCl solution. Significant dependence of the anode electrochemical behavior on the salt concentration in the fuel stream was observed. Condensation of salt droplets on the anode surface and inside the porous anode takes place.