bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of Cathode Kinetics in SOFC: Model Thin Film SrTi1-xFexO3-δ Mixed Conducting Oxides
Authors: Jung WooChul , Tuller Harry L.
Published: April 2011

To understand the kinetics controlling the SOFC cathode processes, a model mixed conducting perovskite materials system, SrTi1-xFexO3-δ, was selected, offering the ability to systematically control both the levels of electronic and ionic electrical conductivity as well as the energy band structure. This, in combination with considerably simplified electrode geometry, served to demonstrate that the rate of oxygen exchange at the surface of SrTi1-xFexO3-δ is only weakly correlated with either high electronic or ionic conductivity, in apparent contradiction with common expectations. On the other hand, evidence was found suggesting the importance of minority electronic species in determining the rate of oxygen exchange. Furthermore, the enrichment of Sr to the surface of the electrodes was found to reduce the oxygen exchange rate constant; this effect becoming more evident with increasing values of x. The observed trends are discussed in relation to the cathodic behavior of MIEC electrodes.
Effect of Gel Viscosity on the LSM Films Supported on Metallic Substrate
Authors: Conceição Leandro , Ribeiro Nielson , Souza Mariana M.
Published: April 2011

This work is a part of the research on the synthesis of multilayer LSM (Lanthanum Strontium Manganite) thin films for SOFC cathode. The films were prepared by sol-gel route, using a concentration of the transition metal salts in the starting solution of 0.18 mol.L−1. This solution was refluxed at 80ºC on a hot plate until a viscosity of 50 or 100 cP was reached. These gels were deposited by dip coating on metallic substrate (SST439 - Cr - 17-19%) at room temperature. After deposition, the LSM/metal-supported composite was heated at 800ºC for 2 h. The structure and morphology of the films were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively, to study the influence of the gel viscosity and the number of layers deposited.
Nanofiber Scaffold for Solid Oxide Fuel Cell Cathode
Authors: Zhi Mingjia , Mariani Nicholas , Gerdes Kirk , Wu Nianquiang
Published: April 2011

Yttria stabilized zirconia (YSZ) and La0.8Sr0.2MnO3 (LSM) nanofibers were prepared by electrospinning method. The diameter of the nanofibers is around 200 nm and tens of microns. The crystal phase and morphology of the nanofibers were examined. The nanofibers exhibit chemical and structural stability at high temperature. The results indicate these nanostructures are promising materials for fabricating high performance solid oxide fuel cell cathode.
Silver Nanomesh as a Cathode for Solid Oxide Fuel Cells
Authors: Shim Joon Hyung , Kim Young Beom , Park Joong Sun , Prinz Fritz B.
Published: April 2011

We have tested a silver nano-mesh with close-packed holes as cathodic catalysts for intermediate temperature solid oxide fuel cells. The nano-mesh structure was fabricated in a close-packed hexagonal array with the pore size of 500~600nm. Fuel cell tests were conducted using the nano-mesh silver cathodes with commercial 100μm-thick 8% yttria stabilized zirconia electrolytes and sputtered porous platinum anodes. Performance of the fuel cells was analyzed by the current-voltage and the potentiostatic current measurements at temperatures of 250~300ºC. We confirmed that the nano-mesh silver cathodes improved fuel cell performance dramatically and enhanced stability against thermal degradation and morphological agglomeration compared to randomly sputtered porous silver cathodes.
Effect of Polarization on Platinum Deposition at LSM/YSZ Interfaces
Authors: Yamaji Katsuhiko , Shimonosono Taro , Kishimoto Haruo , Brito Manuel E. , Horita Teruhisa , Cho Do-Hyong , Izuki Manabu , Wang FangFang , Yokokawa Harumi
Published: April 2011

The effect of polarization on platinum deposition from current collector to triple phase boundaries around LSM/YSZ interfaces was investigated. Button-type half-cells consisting of LSM cathode and 8YSZ electrolyte with platinum mesh current collector was used for polarization tests at T = 1073 K. Fixed voltages of - 0.1 or -0.3 V vs. reference electrode was applied to the cathode during the tests. Abnormal rapid increment of current density was observed at the large polarization of -0.3 V, and normal slow increment of current density was observed at the small polarization of - 0.1 V. Platinum particles are observed at the triple phase boundaries (TPBs) around LSM/YSZ interfaces after the cell test at - 0.3 V for 60 h. On the other hand, platinum particles are not observed around TPBs after the cell test at - 0.1 V for 86 h.
Monitoring Active and Resistive Zones of SOFC Cathodes by Voltage Driven Tracer Incorporation
Authors: Fleig Jürgen , Opitz Alexander , Schintlmeister Arno , Kubicek Markus , Hutter Herbert
Published: April 2011

Information on the active and resistive zones involved in the oxygen reduction reaction at SOFC cathodes is often deduced indirectly, for example from interpretations of impedance spectra or from geometry dependent polarization resistance measurements. A more direct means for obtaining information on the decisive zones is voltage driven tracer incorporation and subsequent spatially resolved analysis of tracer concentrations by secondary ion mass spectrometry. In this contribution it is first discussed under which conditions quantitative data on the width of three phase boundaries (TPB) can be determined. The calculations are then exemplified by measurements on the TPB width of Pt electrodes on YSZ. Moreover, it is shown for Sr-doped LaCoO3-δ cathodes that also resistive regions of oxygen reduction can be visualized by voltage driven tracer studies.
Nanostructured Composite Cathodes by Suspension Plasma Spraying for SOFC Applications
Authors: Soysal Dennis , Ansar Asif , Ilhan Zeynep , Costa Rémi
Published: April 2011

In the metal supported SOFCs (MS-SOFCs), conventional sintering route for cathode layer appears unfeasible due to excessive oxidation of metal support in air at sintering temperatures and degradation of perovkites during sintering in low oxygen partial pressures. The novel process of suspension plasma spraying (SPS), capable of producing a wide variety of coating structures and compositions without any post-deposition sintering, is developed and evaluated in detail for the fabrication of cathode layers for MS-SOFCs. Composite cathodes of LSCF and CGO were developed and the influence of different cathode microstructures on fuel cell performance was examined. Four exemplary cathode coatings have been created, ranging from partially dense with small pores to highly porous layers preserving submicronic agglomerated structures. These cathode coatings have been tested on equal half-cells made of the same anode and electrolyte. The best performing microstructure had a powder density of 798 mW/cm² at 800°C. Microstructural differences could be attributed to different behavior and performance of the coatings.
Study of Ca3-xBixCo4O9+δ(0 < x ≤ 0.5) as Novel Cathodes for IT-SOFCs
Authors: Zou Jing , Park Jungdeok , Yoon Heechul , Choi Seokgon , Chung Jongshik
Published: April 2011

The misfit compound Ca3-xBixCo4O9+δ (CCOBix, x = 0.1-0.5) are synthesized via conventional solid state reaction and investigated as cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs). The powders exhibit good thermal stability, as well as good chemical compatibility with Ce0.8Sm0.2O2-γ electrolyte. The SEM results indicate that the melting point decreased with increased Bi amount. The maximal conductivities are 655.9 S•cm-1 and 917.1 S•cm-1 for CCOBi0.1 and CCOBi0.3, respectively. Among the investigated compositions, Ca2.9Bi0.1Co4O9+δ shows the lowest total polarization resistance values. The preliminary results indicate that Ca2.9Bi0.1Co4O9+δ is a promising candidate as IT-SOFC cathode material.
Influence of SO2 on the Long-Term Durability of SOFC Cathodes
Authors: Liu Run-Ru , Taniguchi Shunsuke , Shiratori Yusuke , Ito Kohei , Sasaki Kazunari
Published: April 2011

Sulfur poisoning effect on the electrochemical performance and long-term durability of SOFC cathodes has been investigated for (La0.8Sr0.2)0.98MnO3 (LSM) and La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) up to 1000 hours. Gradual degradation of performance occurred, associated with the formation of strontium sulfate, which depended on SO2 concentration.
Detailed Electrochemical Analysis of High-Performance Nanoscaled La0.6Sr0.4CoO3-δ Thin Film Cathodes
Authors: Hayd Jan , Guntow Uwe , Ivers-Tiffée Ellen
Published: April 2011

Nanoscaled and nanoporous La0.6Sr0.4CoO3-δ thin film cathodes derived from metal-organic precursors (metal organic deposition, MOD) with a film thickness of 200 nm and an average grain and pore size in the sub 100 nm regime were investigated with the focus on the reaction kinetics by a systematic temperature (400 - 600 ºC) and oxygen atmosphere (pO2
= 0.01 - 0.5 atm) variation. Electrochemical impedance spectroscopy was applied, followed by a detailed data analysis including calculating the distribution function of relaxation times (DRT) and CNLS fit. Five processes were identified. Four processes are temperature activated, whereas one process at low frequencies exhibits a slight deactivation with temperature. Furthermore, the three low and mid frequency processes are oxygen partial pressure dependent, whereas the two high frequency processes remain unaffected by pO2
variations. Extremely low polarization losses as low as ASRpol
= 9 mΩ cm² at 600 ºC were measured in synthetic air.
Comparison of Electrochemical Performances of Electrosprayed LSCF Cathode Films for IT-SOFCs for Different Morphologies and Cobalt Contents
Authors: Marinha Daniel , Dessemond Laurent , Djurado Elisabeth
Published: April 2011

The electrochemical behaviour of La0.6Sr0.4Co1-yFeyO3-d cathodes with y = 0.2 and 0.8 was examined, for two distinct film morphologies, using impedance spectroscopy between 400 and 600° at OCV in air. LSCF films were deposited by Electrostatic Spray Deposition (ESD) technique onto Ce0.9Gd0.1O2-d substrates, resulting in dense and cracked microstructures, with ~2 and ~28 µm in thickness, respectively. The microstructure and composition of the cathodes were found to have significant influence on the impedance responses. The lowest cathode polarization resistance value (0.6 ohm.cm2 at 600°) was determined for the cobalt-rich composition with cracked microstructure, The enhancement is attributed to the increase in cathode surface area, due to the film porosity, and improvement of both the bulk diffusion and surface exchange phenomena due to increase in cobalt content. Activation energies of ~1.1 eV indicated that the cathode reaction is limited by bulk diffusion and surface exchange.
Exploring Mixed Protonic/Electronic Conducting Oxides as Cathode Materials for Intermediate Temperature SOFCs Based on Proton Conducting Electrolytes
Authors: Fabbri Emiliana , Markus Isaac , Bi Lei , Pergolesi Daniele , Traversa Enrico
Published: April 2011

Novel mixed protonic/electronic conducting perovskite oxides, BaZr0.8-xPrxY0.2O3-δ (BZPYx, 0.1 < x < 0.4), were investigated for use as cathode materials in intermediate temperature solid oxide fuel cells (IT-SOFCs) based on proton conducting electrolytes. Chemical stability tests showed that BZPYx oxides were stable in the presence of CO2 and water vapor. Conductivity measurements of BZPYx were performed in wet (3% H2O) air atmosphere using electrochemical impedance spectroscopy analysis. Ionic and electronic transport numbers were calculated from conductivity measurements at different oxygen partial pressures, using an established defect model. For all the compositions, electronic conduction decreased with decreasing the temperature. Varying the Pr content, it was found that the ratio between the electronic and ionic conductivity was dependent on the Pr content, being the electronic conductivity proportional to Pr content.
Nanocomposite Cathode Materials for Intermediate Temperature Solid Oxide Fuel Cells
Authors: Kharlamova Tamara , Pavlova Svetlana , Sadykov Vladislav , Bespalko Yulia , Krieger Tamara A. , Pelipenko Vladimir , Belyaev Vladimir , Muzykantov Vitaly , Alikina Galina , Okhlupin Yury , Uvarov Nikolai , Smirnova Alevtina
Published: April 2011

The present paper is devoted to optimization of composites (100-z) wt.% La1-ySryFe0.7Ni0.3O3-δ - z wt.% Ce0.9Gd0.1O2-δ (GDC) and study of the effect of Sr doping of perovskite and GDC content in the sample on structural and transport features of the composites. The results on the research of structural and microstructural features of the composites and their transport properties by using XRD, HRTEM, EDX analysis, electrical conductivity measurements, oxygen isotope heteroexchange and conductivity as well as weight relaxation techniques are presented and discussed.
Detailed Microstructure Analysis and 3D Simulations of Porous Electrodes
Authors: Joos Jochen , Carraro Thomas , Ender Moses , Rüger Bernd , Weber André , Ivers-Tiffée Ellen
Published: April 2011

The microstructure of a high performance LSCF-cathode is reconstructed using a dual-beam focused ion beam / scanning electron microscopy (FIB/SEM) system. The corrected reconstruction data representing altogether a volume of ~ 2800µm3 are the basis for the calculation of the microstructure parameters (i) volume-specific surface area, (ii) volume/porosity fraction and (iii) tortuosity. An analysis of the influence of the size of the reconstructed volume on the microstructure parameters is performed. Thereby the FIB/SEM data were resampled with different sizes and the influence of the resampling on the parameters is investigated. These parameters constitute the basis to calculate cathode performance via simplified microstructure models (1). However, it would be desirable to fit the reconstructed microstructure directly into a more accurate 3D-model. First results of a 3D finite element method model, which enables a direct use of the corrected 3D FIB/SEM data, are presented here.
Firing Temperature Effect on 3D Microstructure and Performance of LSM-YSZ Composite SOFC Cathodes
Authors: Cronin J. Scott , Muangnapoh Kullachate , Patterson Zach , Yakal-Kremski Kyle , Barnett Scott A.
Published: April 2011

(La0.8Sr0.2)MnO3-Y-stabilized Zirconia (LSM-YSZ) cathodes fired at various temperatures were studied using 3D Focused Ion Beam - Scanning Electron Microscopy (FIB-SEM) tomography and Impedance Spectroscopy (IS). The lowest resistance cathode, fired at 1175°C, had nearly the highest active three-phase boundary density. This optimum was where the firing temperature was sufficient to yield good LSM-particle percolation but not so high as to cause substantial particle coarsening and densification. Increasing the firing temperature above 1175°C caused a shift in the main impedance response from ~100-1000 Hz to 1-10 Hz; this low-frequency response was primarily an electrochemical process, with gas diffusion becoming significant only for low oxygen pressure. Focusing on the low frequency peak for cathodes fired at 1325°C, A-site-deficient LSM yielded lower resistance than stoichiometric LSM. Finally, cathodes were annealed at 1000-1100°C in order to accelerate structural evolution; changes in the impedance response were similar to those observed with increasing firing temperature.
Microstructural Control of Composite Cathode by Wetting Nature of Infiltrated Solutions
Authors: Lee Shiwoo , Miller Nicholas , Manivannan Ayyakkannu
Published: April 2011

Wetting behavior of metal nitrates solution on a SDC-LSCF composite cathode of SOFC was investigated. Electrode overpotential of a fuel cell cathode prepared by infiltration is significantly affected by microstructural modification, which is, in turn, a function of wettability of solution components such as nitrate solution and cation species. Surface energies, which determine characteristic wetting behavior, could be varied by components' surface properties. Preferential wetting behavior expected from a model experiment using dense pellets was reasonably demonstrated for real composite cathodes.
Chemical, Electronic and Nanostructure Dynamics on Sr(Ti1-xFex)O3 Thin-Film Surfaces at High Temperatures
Authors: Chen Yan , Jung Woo Chul , Kuru Yener , Tuller Harry L. , Yildiz Bilge
Published: April 2011

The surface structure, chemical composition and electronic structure of Sr(Ti1-xFex)O3 under different temperatures and oxygen pressures were studied by Scanning Tunneling Microscopy / Spectroscopy (STM/S) and X-ray Photoelectron Spectroscopy (XPS). The surface structure remained stable to 430 oC at 10-3 mbar oxygen pressure. When annealing at low oxygen pressure, the A to B site ratio, Sr/(Fe+Ti) decreased, Fe content at the B site increased, and particles that are likely to be Fe enriched, precipitated to the grain boundaries. Moreover, Fe changed its valance state, in part, from Fe3+ to Fe2+, consistent with oxygen vacancy formation. The surface of STF was electrically insulating at room temperature, and exhibited by STS a well defined gap in the electronic density of states at 380 oC. With further increase to 430 oC, the energy gap disappeared. The variation in surface defects during thermal treatment is discussed as a likely reason for electronic structure changes at elevated temperatures.
Potential and Limitation of Application of Pulsed Laser Deposited Nano-Structure LSC Thin Film Cathode to YSZ Electrolyte SOFC
Authors: Son Ji-Won , Myung Doo-Hwan , Hwang Jaeyeon , Lee Hae-Weon , Lee Jong-Ho
Published: April 2011

Possible solutions to the microstructural instability of single phase lanthanum strontium cobaltite thin film cathode fabricated by pulsed laser deposition are presented. The effect of the deposition parameter variation and the deposition materials change from a single phase to a composite are discussed. By introducing the electrolyte-cathode composite concept to the thin film deposition and employing a gradient cathode structure, much improved stability of the high-temperature electrochemical performance and the microstructure of the thin film cathode could be obtained.
Mechanical Properties of La0.6Sr0.4Co1-yFeyO3-δ under Various Temperatures and Oxygen Partial Pressures
Authors: Kimura Yuta , Kushi Takuto , Hashimoto Shinichi , Watanabe Satoshi , Amezawa Koji , Kawada Tatsuya , Fukuda Yasuhiro , Unemoto Atsushi , Sato Kazuhisa , Yashiro Keiji , Mizusaki Junichiro , Hashida Toshiyuki
Published: April 2011

Young's modulus, shear modulus, Poisson's ratio and internal friction of La0.6Sr0.4CoO3-δ (LSC) and La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF6428) were evaluated in the temperature range between 298 to 1173 K, and the oxygen partial pressure, P(O2), range between 1 x 10-1 to 1 x 10-4 bar using the resonance method. The apparent Young's moduli of LSC and LSCF6428 first decreased with increasing temperature, and then drastically increased at intermediate temperatures. P(O2) dependence of the Young's modulus of LSCF6428 showed different trends depending on temperature. At 873K, the Young's modulus was almost independent of P(O2), while it increased with decreasing P(O2) at 973 K. At 1073 K, it increased down to 5 ×10-3 bar and then decreased in further lower P(O2). At 1173K, it decreased with decreasing P(O2). Such complicated temperature and P(O2) dependences are considered as composite phenomena caused by the lattice expansion/shrinkage, the oxygen nonstoichiometry change, and the phase transition.
Oxide Modification by Alloying Molybdenum to Fe-22Cr-0.5Mn for Solid Oxide Fuel Cell Interconnect
Authors: Yun Dae Won , Seo Hyung Suk , Jun Jae Ho , Lee Jae Myung , Kim Do Hyeong , Kim Kyoo Young
Published: April 2011

The effect of molybdenum addition to Fe-22Cr-0.5Mn ferritic stainless steel on the oxidation, electric property and Cr evaporation was investigated for applications to the solid oxide fuel cell interconnect. Mass gain was measured at 800oC to evaluate the oxidation rate and a 4-probe DC method was used to measure the area specific resistance. Cr and Mo evaporation rate was evaluated by the condensation method. Addition of 0.1 - 4 wt% Mo improved oxidation resistance and electric conductivity. The result suggests that Mo is doped into Cr2O3 layer and changes the defect structure of the layer. The evaporation rate of Cr vapor species was not changed significantly by Mo addition.
High Temperature Oxidation of Plastically Deformed Ferritic Interconnect Steel
Authors: Bexell Ulf , Olsson Mikael , Lundberg Mats W.
Published: April 2011

In this study, thin sheets of a 22% Cr ferritic steel, Sandvik Sanergy HT has been coated with a thin metallic cobalt film. Samples of the coated steel sheet were exposed to two different forming experiments simulating different aspects of sheet metal forming and post high temperature oxidation. The results show that the metallic cobalt film cracks when the steel sheet is subjected to biaxial straining but that the cracks heal at high temperature. Material subjected to modified scratch testing i.e. simulating the contact between sheet metal and forming tool will oxidize in the same manner as non-scratched material. Also, from high temperature corrosion point of view there is no difference between materials formed under lubricated or dry conditions when oxidized. However, from a tribological point of view a lubricated contact situation is preferred.
Multifunctional Nano-Coatings for SOFC Interconnects
Authors: Froitzheim Jan , Svensson Jan-Erik
Published: April 2011

Chromium evaporation from metallic interconnects in SOFCs is commonly poisoning the cathode of SOFCs. To reduce chromium evaporation, rather thick coatings have been deposited using various coating techniques. In this study a 22% Cr ferritic steel has been coated with multilayered nano coatings. The best coatings combine a Cr retention layer (800nm Co) with a 10nm layer of Ce that reduces the corrosion rate of the metallic interconnect. Such coatings might be a cost efficient way to meet the required lifetime targets for SOFC interconnects. The Cr evaporation measurements are carried out with a recently developed denuder technique which allows time resolved quantification of volatile chromium species. Downstream of the samples a denuder tube is placed which collects any CrO2(OH)2 evaporating from the samples.
Synthesis and Characterization of Nanocrystalline MnCo2O4-δ Spinel for Protective Coating Application in SOFC
Authors: Das Sharma Abhijit , Mukhopadhyay Jayanta , Basu Rajendra N.
Published: April 2011

Nanocrystalline (40-50 nm) powders of MnCo2O4-δ spinel have been synthesized through combustion technique at a relatively low temperature. The fuel to oxidant ratio has been optimized by carrying out the combustion reaction under various redox conditions (i.e. varying fuel : nitrate ratio) using different fuels viz., citric acid and glycine. A controlled combustion of the complex gel is achieved under a fuel lean condition using a mixed fuel of glycine and citric acid. Phase pure materials are obtained upon calcination of the ash at a temperature as low as 650degC and the powder can be consolidated to more than 95% of theoretical density at a temperature of only 1100degC. The bulk samples show a linear thermal expansion behaviour (CTE: 13.1 x 10-6 K-1) and a high electrical conductivity (>100 S/cm at 800degC). Crofer22APU interconnect plates are deposited with the synthesized powder using electrophoretic deposition (EPD) technique for protective coating application.
Characteristics of the Sintered Phlogopite Mica/SiO2-B2O3-Al2O3-BaO-La2O3 Glass Blends
Authors: Liu Chien-Kuo , Lin Kin-Fu , Lee Ruey-Yi
Published: April 2011

The thermal and crystalline properties of the sintered Phlogopite mica/SiO2-B2O3-Al2O3-BaO-La2O3 glass blends with the weight fraction of mica from 0 to 100% have been investigated in this paper. A small amount of Phlogopite mica addition raises the coefficient of thermal expansion (CTE) of the sintered phlogopite mica/SiO2-B2O3-Al2O3-BaO-La2O3 glass blends. However, the CTE of the blends decreases as the mica contents higher than 10 wt%. Besides, the CTE of the blends can be modified by adjusting the weight fraction of mica. In this study, the range of CTE varies from 9.7 to 18.1×10−6 ºC−1. The crystalline phases of BaSiO3 and BaAl2Si2O8 are found in the sintered Phlogopite mica/SiO2-B2O3-Al2O3-BaO-La2O3 glass blends. The amount of BaSiO3 phase in the sintered blends is observed at a maximum while the mica contents at 10 wt%. Additionally, the amount of BaAl2Si2O8 phase increases as the mica contents increases.
Characterization of Sr and Ba-Doped LaCrO3 Powders Synthesized by EDTA Method
Authors: Silva Adney Luís A. da , Rocco Ana Maria , Souza Mariana M.
Published: April 2011

Lanthanum chromites are good candidates for electrode application in IT-SOFC. This paper reports the synthesis and characterization of lanthanum chromite powders, doped with strontium and barium, from nitrate precursors by the EDTA method. The samples were synthesized, calcined (800ºC/ 6h), pelletized and sintered at different temperatures. X-ray diffraction patterns showed formation of crystalline perovskite phase, with smaller quantities of secondary phases of SrCrO4 and BaCrO4. The crystallite size calculated using the Scherrer equation is in the range of 23-29 nm. Thermogravimetric analysis revealed that the weight loss is similar for all samples, with complete burn out of organics at 800oC. Scanning electron microscopy showed the presence of agglomerates, formed by particles with low porosity. The electrical conductivity of all samples is similar to the values in the literature.
Lanthanum Chromite Based Ceramic and Glass Composite Interconnects for Solid Oxide Fuel Cells
Authors: Lee Seung-Bok , Pi Seuk-Hoon , Lee Jong-Won , Lim Tak-Hyoung , Park Seok-Joo , Song Rak-Hyun , Park Chong-Ook , Shin Dong-Ryul
Published: April 2011

In this study, LCC (La0.8Ca0.2CrO3) and glass composite interconnects were investigated to improve the sinterablity and electrical conductivity.
Anomalous Sintering Behavior of (Sr0.7La0.3)1-xTiO3+δ Perovskites (0 ≤ x ≤ 0.12)Synthesized by the Pechini Method
Authors: Mori Masashi , Itoh Takanori
Published: April 2011

The crystal structure, phase relationship and sintering characteristics of (Sr0.7La0.3)1-xTiO3 perovskites (0<x<0.12) have been studied using the Pechini method. From the results of high-temperature neutron diffraction analysis, it was clear that (Sr0.7La0.3)TiO3 showed an orthorhombic structure at room temperature and a cubic structure at 450 degree C. (Sr0.7La0.3)0.88TiO3 showed a single perovskite phase and other samples with an A-site deficiency of 0<x<0.08 included Ruddlesden-Popper phases as second phases. Sintering characteristics had a tendency to improve with increasing A-site deficiency. It was found that during sintering, (Sr0.7La0.3)0.88TiO3 expanded anomalously between 1400 degree C and 1500 degree C and for holding times between zero and 10 h at degree C and 1500 degree C. SEM observation of the samples showed that this expansion was caused by pore formation within the samples.
Oxidation Resistance and Mechanical Properties of ZMG232L and Improved Fe-Cr Ferritic Alloys for SOFC Interconnects
Authors: Uehara Toshihiro , Yasuda Nobutaka , Tanaka Shigenori , Yamamura Kazuhiro
Published: April 2011

Metallic materials, especially Fe-Cr ferritic alloys, are promising as interconnect materials of solid oxide fuel cells (SOFCs) operated at around medium temperatures. These metallic materials are usually machined or pressed into various shapes of interconnect parts, and thickness of these parts is often thin. However, the oxidation rate of thin sheet was much higher than that of thick one. Furthermore, higher strength at operating temperature is needed as the sheet is thinner. In this study, mechanical properties and oxidation resistance at operating temperature for ZMGTM232L and improved alloys, 232J3 and 232G10, were investigated.
Metallic Seals: A Possible Alternative Solution for High Temperature Steam Electrolysis
Authors: Reytier Magali , Bruguière Lionel , Lefrancois Michel , Besson Jacques
Published: April 2011

For High Temperature Steam Electrolysis (HTSE), gas tightness largely drives performance and is a critical key to develop this technology. The main difficulties are due to the fact that gas tightness must be achieved at high temperature (~800°C) between metallic components and brittle ceramic materials. The typical sealing solution relies on glass-based seals despite a large number of drawbacks. Metallic solutions have also been studied but without specific developments as they may be too stiff and too hard to be used together with ceramics. A sealing solution based on a specific metallic seal has been developed and is presented here. Using specific tightness tests, it is shown that this new seal remains tight enough during cooling from 800°C to 400°C and that the cell electrolyte can sustain the seating load. This metallic seal offers an alternative solution for HTSE stacks.
Biogas Fuel Reforming for Solid Oxide Fuel Cells
Authors: Murphy Danielle M. , Richards Amy E. , Colclasure Andrew M. , Rosensteel Wade , Sullivan Neal
Published: April 2011

In this paper, several strategies for biogas reforming and their ensuing effects on solid-oxide-fuel-cell performance are explored. Synthesized biogas (65% CH4 + 35% CO2) fuel streams are reformed over a rhodium catalyst supported on a porous alumina-foam support. Reforming approaches include steam reforming and catalytic partial oxidation utilizing either air or pure oxygen as the oxidant. A computation model is developed and utilized to guide definition of reforming conditions that maximize both CH4 and CO2 conversion. Model predictions are validated with experimental measurements over a wide range of biogas-reforming conditions. It is shown that higher reforming temperatures activate the CO2 in the biogas through dry-reforming reactions. Such dry-reforming chemistry leads to high CO content in the reformate streams, extensive water-gas shift reactions within the SOFC anode structure, and high SOFC power density.
Biomass Conversion in a Solid Oxide Fuel Cell
Authors: Alexander Brentan R. , Mitchell Reginald , Gür Turgut M.
Published: April 2011

Samples of biomass from rice straw, wood, and almond shell were directly converted within a solid oxide fuel cell. Measurements of cell performance indicate that for both wood and almond shell samples, a peak power density of 32 and 33 mW/cm2, respectively, was achieved. These results compare favorably with a measured peak power density of 38 mW/cm2 for an activated carbon fuel. EIS measurements verified the DC results and indicated that performance losses from the biomass samples can be attributed to higher resistances at the anode due to both changes in bed reactivity and mass transport parameters. Comparison with previous studies reveals substantial promise for producing a biomass fueled SOFC device with practical applications.
Sorbents for BioFueled SOFCs
Authors: Alptekin Gokhan , Jayaraman Ambalavanan , Schaefer Matthew
Published: April 2011

Unlike internal combustion engines, fuel cells operate with very high efficiency even at small scale, offering significant benefits to distributed combined heat and power (CHP) systems utilizing bio-waste. However, effective utilization of biogas in a fuel cell requires removal of impurities such as sulfur and siloxanes. TDA Research Inc. (TDA) is developing a low-cost, high-capacity expendable sorbent that can remove both the
H2S and organic sulfur species in biogas to the ppb levels. This sorbent bed operates downstream of a bulk desulfurization system as a polishing bed to provide an essentially sulfur-free gas to the fuel cell. The sorbent can also be modified so that it can remove contaminants such as siloxanes in a single step. TDA is carrying out field demonstrations of our integrated gas clean-up units and biofueled SOFCs. The results from the sorbent development for biogas and field demonstrations will be presented in the meeting.
Influence of Operation Conditions on Carbon Deposition in SOFCs Fuelled by Tar-Containing Biosyngas
Authors: Liu Ming , Millan-Agorio M. G. , Aravind P.V. , Brandon N.P.
Published: April 2011

This paper presents the influence of operation conditions including steam levels, current density and operating time on the performance of Solid Oxide Fuel Cells (SOFCs) fuelled by tar- containing biosyngas. The performance of SOFCs was evaluated by means of recording impedance spectra and polarization curves of the cells before and after tar exposure. The biosyngas composition and the tar concentration used in the measurements were experimentally measured from a commercial gasifier. The results show that increases steam level and current load would reduce the risk of carbon deposition arising from the tar-containing biosyngas. Deposited carbon was found by the change in impedance and by Scanning Electron Microscopy. SOFCs fed by the biosyngas with a high tar level are not expected to be operated for a long term, because this operation resulted in a severe carbon deposition on the anodes.
An Electrochemical Model of Anode Supported Microtubular SOFCs Powered by Ammonia
Authors: Huo J. Y. , Zhou Xiao-Dong
Published: April 2011

A 2-D model considering momentum conservation, mass transport and electrochemical reactions, has been established for tubular solid oxide fuel cells with ammonia as the fuel. The gas-diffusion in two directions has been investigated. One direction is the axial direction (along the tube), while the other is the radial direction (perpendicular to the tube). With respect to the reactions, we take consideration of both ammonia decomposition within the anode and electrochemical reactions at triple phase boundaries. Results of our model showed the concentration profile of gas species both axial and radial directions. The electrochemical reactions were then incorporated with mass transport to provide an insight view to evaluate the electrochemical performance of ammonia-fed SOFCs as functions of the operating temperature and anode microstructure.
Design and Testing of Structured Catalysts for Internal Reforming of CH4 in Intermediate Temperature Solid Oxide Fuel Cells (IT SOFC)
Authors: Smirnova Alevtina , Sadykov Vladislav , Mezentseva Natalia , Bunina Rimma , Pilipenko V. V. , Alikina Galina , Krieger Tamara A. , Bobrova L. N. , Smorygo Oleg L. , Van Berkel Frans , Rietveld B.
Published: April 2011

Procedures for the synthesis of nanocomposite anode materials comprised of Ni-YSZ promoted by doped Ce-Zr-O fluorite-like or La-Pr-Mn-Cr-O perovskite-like oxides and Pt/Ru were elaborated. Their composition, structure, reactivity, and catalytic properties in CH4 steam reforming were characterized using various techniques, such as SEM, TEM, EDX, TPR, and I-V testing in SOFC conditions. The optimized nanocomposites supported on compressed foam Ni-Al substrates demonstrated high and stable performance at H2O:CH4=1:2 ratio without coking or sintering. For the SOFC testing, the planar catalytic substrates with the surface area of 5x5 cm2 have been used. The demonstrated SOFC performance in the internal CH4 reforming mode was close to the performace obtained with the humidified hydrogen. The achieved power density was up to 300-800 mW/cm2 at 600-800 oC meeting the targets of the area specific resistance, fuel effficiency, and power density.
Effect of Hydrogen Sulfide on Electrochemical Oxidation of Syngas for SOFC Applications
Authors: Roushanafshar Milad , Luo Jing-Li , Chuang Karl T , Sanger Alan R
Published: April 2011

Addition of 0.5% hydrogen sulfide into syngas improved the performance of a oxygen conducting solid oxide fuel cell by enhancing the electrochemical oxidation of carbon monoxide. However, there was no consumption of hydrogen sulfide, as determined by mass spectrometric and gas chromatographic analyzes of the effluent gases during potentioidynamic and potentiostatic runs. The anode was a composite of lanthanum strontium titanate and yttrium cerium oxide. The electrochemical performance of the fuel cell fuelled with syngas containing 0.5% hydrogen sulfide was stable during 30 h galvanostatic tests.
Analysis of Fuel Options for SOFC-Based Power Systems in Undersea Vehicles
Authors: Burke Alan , Carreiro Louis
Published: April 2011

In a departure from NUWCDIVNPT's original focus on diesel-type (logistics) fuels, methane is looking more attractive for Unmanned Undersea Vehicle (UUV) applications, at least for first generation SOFC-powered UUVs. Even though the energy density for methane is roughly half that of diesel-type fuel, the savings in oxygen and carbon dioxide sorbent storage result in system energy metrics similar to those for S-8-based systems. In addition, the fuel processor control and system start-up can be greatly facilitated by using methane instead of a liquid hydrocarbon fuel. Switching to a methane fuel feed has the following advantages: • High Hydrogen-to-Carbon ratio (this lowers O2 and CO2 sorbent storage requirements) • Facilitates steam reforming versus diesel-type fuels • Greater ease of start-up and system power transient control • Risk mitigation for potential SOFC coking • Low boiling point, thus avoiding logistics of vaporizing diesel-type fuels and producing carbon residue.
Non-Thermal Plasma Reformation of Liquid Fuels
Authors: Hartvigsen Joseph , Elangovan S. , Hollist Michele , Czernichowski Piotr , Frost Lyman
Published: April 2011

Ceramatec has investigated the use of a non-thermal plasma reformer capable of processing Mil-Spec JP-8 (up to 3000 ppmw sulfur) into a stream of synthesis gas appropriate for a high temperature fuel cell. The plasma reformer is sulfur tolerant and liquid phase sulfur removal or hydro-desulfurization is not required prior to reformer operation. The unit is capable of a cold start. The reformer uses the non-thermal plasma to form radicals to promote reforming much as would occur with a solid reforming catalyst. The plasma unit has the advantages of being fuel flexible, and being capable of operating in a number of orientations for packaging. Reformer sizes ranging from 5 to 100 kWt have been operated successfully using JP-8 fuel.
Low Temperature Direct Methanol Fuel Cell with YSZ Electrolyte
Authors: Komadina Jason , Kim Young Beom , Park Joong Sun , Gür Turgut M. , Kang Sangkyun , Prinz Fritz B.
Published: April 2011

Direct methanol operation of an oxide ion conducting ceramic electrolyte fuel cell was studied at moderately low temperatures. The fuel cell architecture was comprised of a platinum cathode patterned by nanosphere lithography, a polycrystalline yttria-stabilized zirconia (YSZ) electrolyte, and a sputtered porous Pt0.4Ru0.6 anode. Fuel cell behavior and electrochemical impedance spectra (EIS) were measured. We observed maximum power densities of approximately 2 uW/cm2 and 480 uW/cm2 at 250°C and 450°C, respectively. Under H2 fueling conditions, we observed power densities of 1 mW/cm2 at 450°C. These results are consistent with the literature for similar cells and relative performance when using methanol. We speculate that anode reactions involving Ru may contribute significantly to the observed cell impedance.
Performance and Durability of High Temperature Steam Electrolysis: From the Single Cell to Short-Stack Scale
Authors: Petitjean Marie , Reytier Magali , Chatroux André , Bruguière Lionel , Mansuy Aurore , Sassoulas Hervé , Di Iorio Stéphane , Morel Bertrand , Mougin Julie
Published: April 2011

A new stack designed for High Temperature Steam Electrolysis is presented here. It integrates grids as contact layers and an optimized sealing solution. The design has first been validated at the SRU level before operating a 5-cell stack for a performance and durability test. Performance results show that i-V curves at the SRU and stack level are very close to those obtained at the single cell level, highlighting an optimized design and more specifically good contacts between the interconnects and the cells. Very high performances have been obtained (-1 A/cm² at 1.2-1.3 V at 800°C) at the stack level and more than 99% of the produced hydrogen has been collected. A durability test of 2700 hours has been carried out with a current density of -0.5 A/cm² and a steam conversion rate of 25%. Degradation rates around 7-13 %/kh for the 3 central cells have been measured during this test.
Long Term Testing of Short Stacks with Solid Oxide Cells for Water Electrolysis
Authors: Schefold Josef , Brisse Annabelle , Zahid Mohsine , Ouweltjes Jan Peter , Nielsen Jens Ulrik
Published: April 2011

Results from a 4000 h test of a solid oxide fuel cell (SOFC) stack operated in the H2O electrolyser mode are reported. The stack, which consisted of 5 cells with electrolyte supported cells of each 100 cm2 active area, was operated at 820°C under a current density of -0.4 Acm-2, an absolute feed gas humidity of 90%, and a steam conversion of 40%. Faradaic efficiencies close to 100% and initial cell voltages of ~1.2 V were achieved, which translates to high electrical-to-chemical energy conversion efficiency. Average (cell + interconnect) voltage degradation under constant current operation amounted to 5.6% per 1000 h. The cell specific, partly reversible, voltage evolution with time together with impedance spectroscopic results indicates that a significant part of degradation arises from ohmic losses at the cell interconnects. The response of the stack to a loss of steam supply under current flow is described and post-mortem analysis is reported.
Hydrogen and Power by Fuel-Assisted Electrolysis Using Solid Oxide Fuel Cells
Authors: Tao Greg , Butler Bruce , Virkar Anil
Published: April 2011

Solid oxide fuel cell (SOFC) operation in three modes is described: Power generation (SOFC), conventional electrolysis (SOEC), and fuel-assisted electrolysis (SOFEC). In the SOFEC mode, part of the applied voltage is replaced by chemical potential difference as the driving force. Steam is supplied at the oxygen supplying electrode. A combined 1 kW scale power generation - hydrogen production unit has been demonstrated.
Model-Based Evaluation of the Production of Pure Oxygen through SOFC/SOEC Integration
Authors: Taher Mohamed A. , Adjiman Claire , Iora Paolo , Chiesa Paolo , Brandon N.P.
Published: April 2011

Oxygen is used for a wide range of applications. Depending on the economic range and the required purity, various methods are used to extract oxygen; for the medium to large production scale, cryogenic air separation is preferred with relatively low energy consumption and high purity, whilst for the small scale, adsorption-based devices are widely used, with higher energy consumption and a lower purity product. A novel process capable of producing pure oxygen via the integration of SOFC and SOEC is evaluated in this paper using gPROMS ModelBuilder. Furthermore, a sensitivity analysis to study the effects of some of the important operating conditions was conducted. With a predicted electrical energy consumption of 0.21-0.34 kWh/ kg O2, this new approach is shown to be a good candidate to compete with the non-cryogenic small scale production technologies in terms of energy consumption, with the additional advantage of producing high purity oxygen.
Silicon Spintronics: Challenges and Perspectives
Authors: Fabian Jaroslav
Published: April 2011

Spintronics has significantly advanced our understanding of the electronic spin phenomena in metals and semiconductors. It has also given practical magnetoelectronic devices, as symbolized by the giant magnetoresistance (GMR) and tunneling magnetoresistance (TMR) read heads working in the hard drives. These practical devices comprise ferromagnetic metal layers separated by other metals or insulators. The next advance should involve semiconductors. Special attention is paid to silicon, due to its dominance in the information technology and favorable spin properties.
Trends and Challenges in Si and Hetero-Junction Tunnel Field Effect Transistors
Authors: Claeys Cor , Leonelli Daniele , Rooyackers Rita , Vandooren Anne , Verhulst Anne , Heyns Marc , Groeseneken Guido , De Gendt Stefan
Published: April 2011

This paper gives an overview of the different trends and challenges of fully Si-based and hetero-junction tunnel field effect transistors (TFETs). The different horizontal and vertical approaches are discussed in view of processing aspects and device performance. A benchmarking is given of the state-of-the-art experimental data reported in the literature, enabling to highlight the potentials of these emerging devices.
SiGe and Ge on Insulator Wafers
Authors: Daval Nicolas , Figuet Christophe , Aulnette Cécile , Landru Didier , Drazek Charlotte , Bourdelle Konstantin K. , Guiot Eric , Letertre Fabrice , Nguyen Bich-Yen , Mazure Carlos
Published: April 2011

This paper discusses the options to boost performances of PMOS in Fully Depleted CMOS via introduction of a SiGe compressively strained layer, specifically studying thickness uniformity of such SiGe layers. In a second part we discuss GeOI substrates as a substrate of choice for Ge PFET / IIIV NFET co-integration for future CMOS nodes, and its possible manufacturing using condensation method.
Lateral-Liquid Phase Epitaxy of (101) Ge-On-Insulator from Si Template by Metal-Induced Crystallization
Authors: Kurosawa Masashi , Kawabata Naoyuki , Kato Ryusuke , Sadoh Taizoh , Miyao Masanobu
Published: April 2011

We investigate metal-induced lateral crystallization (MILC) of Si on insulator to achieve (101) oriented Si films. Moreover, we demonstrate the lateral liquid phase epitaxy of high quality Ge(101) layers by using the MILC-Si films as crystal seed. This technique will be employed to realize high-speed thin-film transistors with Ge channel.
A Simulation Comparison between Junctionless and Inversion-Mode MuGFETs
Authors: Colinge Jean-Pierre , Kranti Abhinav , Yan Ran , Ferain Isabelle , Dehdashti Akhavan Nima , Razavi Pedram , Lee Chi-Woo , Yu Ran , Colinge Cindy
Published: April 2011

A new type of multigate MOSFET, called the junctionless nanowire transistor (JNT), has recently been proposed. It avoids junction formation problem and can be used to make very short-channel devices. Here, we compare the properties and performances of junctionless nanowire transistors with those of with Π-gate inversion-mode (IM) devices. The performances of silicon JNTs and IM transistors are evaluated in terms of short-channel effects, current drive, and gate capacitance. Junctionless devices are shown to have smaller short-channel effects than inversion-mode transistors with junctions. Comparison of carrier transport in the channel is made between junctionless nanowires and inversion-mode multigate field-effect transistors, and the benefits/drawbacks of bulk transport vs. surface transport are addressed.
Comparative Study of Random Telegraph Noise in Junctionless and Inversion-Mode MuGFETs
Authors: Nazarov Aleksey , Lee Chi-Woo , Kranti Abhinav , Ferain Isabelle , Yan Ran , Dehdashti Akhavan Nima , Razavi Pedram , Yu Ran , Colinge Jean-Pierre
Published: April 2011

Random telegraph-signal noise (RTN) is observed in n-channel junctionless metal-oxide-silicon field effect transistors (MOSFETs) and n-channel inversion-mode MOSFETs fabricated in the same technological process on UNIBOND® SOI wafers as a function of gate and drain voltages and measurement temperature. It is shown that the RTN of the drain current in the JL transistor operating in linear mode begins to appear when the transistor starts to form an accumulation channel and has considerable lower amplitude than in the IM MOSFET. On the basis of analysis of the average charge capture and emission time of the charge from the traps responsible for the RTN the main parameters of the traps are determined.
Novel SOI Structures and Characterization Strategy
Authors: Cristoloveanu Sorin
Published: April 2011

Innovative SOI materials and devices are reviewed with special attention to their electrical characterization. Appropriate measure-ment techniques and accurate interpretation of the experimental data are necessary steps for evaluating nanosize devices. Informative examples are selected from various structures including ultrathin SOI and GeOI, strained MOSFETs, multiple-gate transistors, nanowires, tunneling and memory devices.