bluuebunny/crossref_metadata_2025 huggingface dataset:
Modelling Potential, Current and Gas Velocity Distributions in Micro-Tubular Hollow Fiber SOFC Stacks
Authors: Doraswami Uttam , Droushiotis Nicolas D. , Kelsall Geoff
Published: September 2009

Micro-tubular solid oxide fuel cells of ca.1 mm diameter offer high volumetric power densities and tolerance to rapid thermal cycling, making them attractive as micro-power sources. Mathematical models accounting for charge, mass, energy and momentum balances, developed to predict single hollow fiber (HF)-SOFC behavior, have been extended to micro-tubular fuel cell stacks, mainly to study the effects of stack configuration on potential, current and velocity distributions. A stack design based on embedding of cells in a cathode matrix was predicted to perform well, producing 0.3 W for a 2Xseries by 2Xparallel stack of 5 mm long cells (1.79 W cm-3), performance being very sensitive to material conductivity and cross-sectional area of the series interconnect. A novel stack design with equal active surface area proposed herein, was predicted to perform less well, producing ca. 0.2 W for a 2Xparallel stack of 10mm long cells, primarily due to axial electrode potential losses.
Coupling Complex Reformer Chemical Kinetics with Three-Dimensional Computational Fluid Dynamics
Authors: Goldin Graham , Zhu Huayang , Kattke Kyle , Dean Anthony , Braun Robert , Kee Robert J. , Zhang Dan , Maier Lubow , Deutschmann Olaf
Published: September 2009

A new capability is developed that enables the modeling of hydrocarbon fuel reforming for certain reactor geometries. The system described in this paper considers a shell-and-tube configuration for which the catalytic reforming chemistry is confined within the tubes. The models are designed to accommodate detailed gas-phase and catalytic reaction kinetics, possibly including hundreds of species and thousands of reactions. The shell flow can be geometrically complex, but does not involve any complex chemistry. An iterative coupling algorithm is developed with which the geometrically complex flow is modeled with FLUENT and the chemically complex reforming is confined to straight tubes. The paper illustrates the model using propane partial oxidation and reforming as an example.
Numerical Simulation of Intermediate-Temperature Disk Type Seal-less SOFC Using Pure Hydrogen Considering Air Back Diffusion Phenomenon
Authors: Tanaka Tadashi , Inui Yoshitaka , Chitose Norihisa , Akbay Taner
Published: September 2009

A one-dimensional simulation code for single cell intermediate-temperature disk-type seal-less SOFC is improved to include the air back diffusion phenomenon, which implies the diffusion of air into the fuel channel due to the mixing of the anode and cathode exhaust gases and the complete oxidation of hydrogen at the seal-less edge of the cell. The numerically obtained current density-single cell voltage (i -V) characteristic curves coincide well with the experimental ones. The effect of the air back diffusion phenomenon on the cell performance is investigated. It is revealed that the single cell voltage reduction due to the air back diffusion phenomenon is negligible under normal operating conditions. However, it is made clear that the reduction of single cell voltage caused by the air back diffusion phenomenon becomes significant when the cell is operated under low fuel utilization conditions.
Micro-tubular SOFCs to Measure the Effects of Cross Flow on Mass Transfer Rates Around the Perimeter of a Cylindrical Electrode
Authors: Lawlor Vincent , Meissner Dieter , Hochenauer Christoph , Griesser Stefan , Cordiner Stefano , Mariani Alessandro , Zauner Gerald , Olabi Abdul , Buchinger Gerhard
Published: September 2009

Micro-Tubular-Solid-Oxide-Fuel-Cells (MT-SOFCs) are primarily being developed to be used as electricity producing devices. However, they are also an ideal tool for investigating the effects of gas cross flows, with various Reynolds numbers and specie concentrations, on the mass transfer rates around the perimeter of a high temperature cylindrical electrode. The SOFC research group at the Upper Austrian University of Applied Sciences in Wels and partners are currently developing multi-cathode and multi-cell methods to measure the concentration of oxygen around the perimeter of these active electrodes. This paper will introduce the reader to computational fluid dynamic (CFD) simulation results that have been used to design an experimental apparatus and some novel MT-SOFC innovations that will be used in the very near future to make experimental measurements to validate the shown CFD simulation results for oxygen concentration around the perimeter of a cylindrical electrode in cross-flow.
Simulations of Heat and Mass Transfers in Tubular Solid Oxide Electrolysis Cell
Authors: Klein Jean-Marie , Deseure Jonathan , Bultel Yann
Published: September 2009

A model of a singular cell of an anode support SOEC is proposed in this work. The results of simulations will allow us to understand and to analyze the ionic and electronic ohmic drops effects on the cell performances. This paper proposes a model solution using the CFD-Ace+ software package to simulate the behaviour of this tubular SOEC. Modelling is based on solving conservation equations of mass, momentum, energy, species and electric current by using a finite volume approach on 3D grids of arbitrary topology. The electrochemistry in porous electrodes is described using Butler-Volmer equations at the triple phase boundary. The layout in 3D of the current densities, the electronic and ionic potentials allow the analysis of the respective ohmic drops. The simulation results emphasize the critical behaviour of SOEC such as the endothermic, exothermic and thermo-neutral operating mode.
Electromotive Potential Distribution and Electronic Leak Currents in Working YSZ Based SOCs
Authors: Mogensen Mogens , Jacobsen Torben
Published: September 2009

The size of electronic leak currents through the YSZ electrolyte of solid oxide cells have been calculated using basic solid state electrochemical relations and literature data. The distribution of the electromotive potential, of Galvani potential, of concentration of electrons, e, and electron holes, h, was also calculated as these parameters are the basis for the understanding of the electronic conductivity that causes the electronic leak currents. The results are illustrated with examples. The effects of electrolyte thickness, temperature and cell voltage on the electronic leak current density are reported.
Simulation of a Tubular Solid Oxide Fuel Cell Stack Operating on Biomass Syn-gas using Aspen Plus
Authors: Doherty Wayne G. , Reynolds Anthony , Kennedy David
Published: September 2009

A tubular solid oxide fuel cell (SOFC) stack is modelled and its operation on biomass syn-gas is investigated. The objective of this work is to develop a computer simulation model of a biomass gasification-SOFC (BG-SOFC) system capable of predicting performance under various operating conditions and using diverse fuels. The stack is modelled using Aspen Plus and considers ohmic, activation and concentration losses. It is validated against published data for operation on natural gas. Operating parameters such as fuel and air utilisation factor (Uf and Ua), current density (j) and steam to carbon ratio (STCR) are varied and have significant influence. The model is run on wood and miscanthus syn-gas. The results indicate that there must be a trade-off between voltage, efficiency and power with respect to j and the stack should be operated at low STCR and high Uf. High efficiencies are predicted making these systems very promising.
Effective Transport Coefficients for Porous Microstructures in Solid Oxide Fuel Cells
Authors: Choi Hae-Won , Berson Arganthaël , Kenney Ben , Pharoah Jon , Beale Steven , Karan Kunal
Published: September 2009

A numerical framework to compute the effective transport coefficients for porous electrode microstructures is presented. The anode and cathode electrodes of solid oxide fuel cells are discretized as porous microstructures that are formed by randomly distributed and overlapping spheres with particle size distributions that match those of actual ceramic powders. The technique involves the construction of the composite electrode microstructure based on measureable starting parameters and the subsequent numerical evaluation of the effective transport coefficients. We use both the finite volume method and the Monte-Carlo simulation to enumerate effective transport coefficients. The results of the calculations are compared with experimental data for electron conductivities for a range of solid-matrix compositions. Comparisons are also made with theoretical correlations for effective coefficients. The effect of Knudsen diffusion on effective gas diffusivity is also addressed in this paper. Numerical results are compared with a harmonic average approximation based on Bosanquet's formula.
Oxidation and Creep Behavior of Porous E-Brite for Solid-Oxide Fuel Cell Interconnects
Authors: Scott Justin A. , Dunand David
Published: September 2009

The effects of isothermal oxidation on the creep response and porosity of E-Brite foams at 800 ºC were investigated. Samples of 43.2 % and 51.4 % porosity were first oxidized in static laboratory air up to 200 hours to determine oxidation kinetics. Select samples were removed after 10 and 100 hours of oxidation and then creep tested to characterize the impact of scale growth on mechanical response and changes in porosity. Significant creep strengthening was observed even when minimal oxide growth occurred. Although oxide growth led to reduced pore size and choked fenestrations, the reduction in open porosity after 200 hours of exposure remained less than 10 %.
Thermal Spray Processes and Materials for Coating Applications of SOFC Components
Authors: Gindrat Malko , Refke Arno , Sabouni Omar , Damani Rajiv , Höle Hans-Michael
Published: September 2009

The production of high quality coatings for fuel cell applications in an industrial scale requires stable, reliable and economically efficient processes. In the recent years, Sulzer Metco has been actively developing coating solutions to fulfill the requirements of fuel cells coating production, in particular for SOFC applications based on both metal and ceramic supported cells. This includes the use of new thermal spray technologies such as LPPS®-Thin Film and TriplexPro{trade mark, serif}-200 to produce the functional layers of fuel cells, such as the electrodes, electrolytes and diffusion barrier layers. In parallel, the development of new powder materials specifically designed towards optimized coating process and functionality has shown an improvement of the cell performance. Both coating technologies have a high potential regarding economical coating production on an industrial large volume scale. This paper presents the current status of developments of the advanced coating technologies together with an overview of the used materials and analysis of the applied coatings.
Oxidation Resistance Coating of Low Sinterability Conducting Ceramics by Aerosol Deposition on SOFC Metallic Interconnector
Authors: Choi Jong-Jin , Choi Joon-Hwan , Ryu Jungho , Hahn Byung-Dong , Yoon Woon-Ha , Lee Byoung-Kuk , Park Dong-Soo
Published: September 2009

Conducting perovskite La0.8Sr0.2MnO3-YSZ (LSM-YSZ) and LaNiO3 (LNO) thick films, 2~6 μm in thickness, were deposited on ferritic stainless steel (SS) by aerosol deposition (AD), as oxidation-resistant coatings on the metallic interconnector of a solid oxide fuel cell (SOFC). The interface microstructure and composition of the coated layer and the STS444 steel after oxidation at 800oC in air were examined, as were the subsequent electrical resistivity changes at an SOFC operating temperature of 800oC in air.
Characteristics of a Protective Coating on Metal Interconnect for SOFCs
Authors: Hong Jong E. , Lim Tak-Hyung , Lee Seung-Bok , Shin Dong-Ryul , Song Rak-Hyun
Published: September 2009

We investigated the influences of metallic coating of cobalt deposited on the ferritic stainless steel, SUS 444, by electrodeposition. Cobalt electrodeposited sample revealed a lower area specific resistance value than that of uncoated at 800°in air and showed efficient retention capability of chromium evaporation. Also, cobalt was oxidized to CoCo2O4 and mixed oxide spinels after 1000h at 800° in air.
APS Deposition of MnCo2O4 on Commercial Alloys K41X used as Solid Oxide Fuel Cell Interconnect: The Importance of Post Heat-treatment for Densification of the Protective Layer
Authors: Saoutieff Elise , Bertrand Ghislaine , Zahid Mohsine , Gautier Ludmila
Published: September 2009

The continuous contamination of the cathode with chromium released from metallic interconnects speeds up the degradation of the performance of the cell. For this reason Solid Oxide Fuel Cell (SOFC) interconnects are coated with a dense protective layer. This layer plays the role of a diffusion barrier for the chromium evaporation at operating conditions. The deposition of a dense, gas tight and stable MnCo2O4 spinel layer on ferritic alloy using the atmospheric plasma spraying (APS) process is studied. The first experimental results show that the plasma spray process combined with an appropriate post thermal-treatment is suitable to form a dense spinel protective layer.
Reduction of Chromium Evaporation with Manganese-based Coatings
Authors: Trebbels Rene , Markus Torsten , Singheiser Lorenz
Published: September 2009

The vaporization of Cr-rich volatile species from interconnector materials for high temperature SOFC`s is considered to be a major source of degradation that limits the lifetime of planar SOFC systems [1-6]. For a longer lifetime of these systems, the Cr vaporization of interconnector material shall be reduced [7]. The potential of reduction of the Cr vaporization using coatings with spinel layers is the subject of the present work. In this study the Crofer22APU, IT-11 and F17 TNB interconnector steel is coated with Mn3O4 and (Mn,Co,Fe)3O4 powder as protective layer and LCC10 and LCC13 as contact layer. The coatings were done with wet powder spraying technique (wps) and atmospheric plasma spraying technique (aps). The Cr vaporization rates were studied at 800{degree sign}C in air using the transpiration method. The measured Cr release of the coated samples was compared to uncoated samples. By using Mn3O4 the Cr vaporization rate was found to be 1 order of magnitude lower than uncoated steel. By using (Mn,Co,Fe)3O4 the Cr vaporization rate was found to be 2 orders of magnitude lower than uncoated steel. The Cr-evaporation is depended on the coating technique
Cr Evaporation of Metallic Interconnects: A Novel Method for Quantification
Authors: Froitzheim Jan , Larsson Erik , Johansson Lars-Gunnar , Svensson Jan-Erik
Published: September 2009

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 thin films (<1µm) of metallic cobalt. The Cr evaporation measurements are carried out with a 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. The experiments are carried out at 850{degree sign}C in a N2-20%O2-3%H2O atmosphere. The investigated Co coatings proved to be very efficient and reduce the Cr evaporation by approxiamatly 90%. Microscopic studies show that both coated and uncoated samples develop two-layered oxide scales with the bottom part consisting of Cr-rich corundum type oxide. The uncoated samples develop a top layer consisting of (Cr,Mn)3O4 oxide while the Co coated samples exhibit a top layer consisting of (Co,Mn)3O4.
Interface Resistance between FeCr Interconnects and La0.85Sr0.15Mn1.1O3
Authors: Mikkelsen Lars , Neufeld Kai , Vang Hendriksen Peter
Published: September 2009

The long term oxidation behaviour and the electrical interface resistance between FeCr interconnects and La0,85Sr0,15Mn1,1O3 plates was studied by a DC four-point method in air at 750{degree sign}C for 10000 h. The tested FeCr alloys were: Crofer 22 APU, Sanergy HT, Plansee IT10, Plansee IT11, and Plansee IT14. The alloys were slurry sprayed with a dual layer coating consisting of an inner Co3O4 layer and an outer layer consisting of La0,85Sr0,15Mn1,1O3 with some Co3O4 added. The microstructure and composition of the oxide scales formed at the interfaces were investigated using SEM/EDX analysis. Low degradation rates of less than 1 mΩcm2/1000 h were measured on all interfaces. The microstructure analysis showed that a duplex Cr2O3-(Mn,Co,Cr)3O4 oxide scale with a thickness of 3-5 µm had evolved on the alloys.
Long-Term Oxidation Behavior of Fe-Cr Ferritic Alloy ZMG232L for SOFC Interconnects
Authors: Uehara Toshihiro , Yasuda Nobutaka , 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 long-term oxidation behavior of Fe-22%Cr ferritic alloy, ZMG232L, was investigated. The oxidation rate of thin sheet was much higher than that of thick one. The effect of Cr content on oxidation resistance of ZMG232L was also investigated. The oxidation rate of low Cr alloy was higher than that of high Cr one. Therefore it was found that such accelerated oxidation occurred because Cr content decreased under oxide layer of edge part of thin sheet and Cr oxide became unstable and Fe was mainly oxidized.
The Effect of Tungsten Addition on the Oxidation Behavior of Fe-22Cr-0.5Mn Ferritic Stainless Steel
Authors: Yun Dae Won , Seo Hyung Suk , Jun Jae Ho , Lee Jae Myung , Kim Do-Hyeoung , Kim Kyoo Young
Published: September 2009

The effect of tungsten addition to Fe-22Cr-0.5Mn ferritic stainless steel on the oxidation, electric property and Cr evaporation was investigated for application to the solid oxide fuel cell (SOFC) 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 (ASR). Cr evaporation rate was evaluated by the condensation method. Addition of 4 wt% W reduced the oxidation rate of Fe-22Cr-0.5Mn steel. The evaporation rate of Cr vapor species and ASR were also reduced. Chi (χ) phase, which precipitated at the grain boundary near the interface between the oxide layer and substrate steel, seems to be responsible for suppressing the fast diffusion of Cr, so that the surface Cr content was reduced while Mn content was increased. This reduced Cr content at the surface is responsible for the lower Cr evaporation rate and ASR.
Synthesis and Characterization of a Spinel Type Cr-Free Ceramic Interconnect Material for SOFCs
Authors: Yoon Mi Young , Yoon Jong Seol , Song Rak-Hyun , Shin Dong-Ryul , Moon Ji-Woong , Hwang Hae-Jin
Published: September 2009

A MnCo2O4 powder was synthesized via a glycine nitrate process (GNP) from manganese and cobalt nitrates. Single phase spinel was obtained by calcining an ash at 800oC and almost fully densified MnCo2O4 was fabricated at 1100oC. It was found that the sintering at higher temperature than 1100oC leads to the decomposition of the MnCo2O4. The MnCo2O4 showed compatible thermal expansion coefficient and good electrical conductivity. However, the phase stability under the reducing environments was proved to be poor.
New Glass Ceramic Sealants for SOFC
Authors: Goedeke Dieter , Besinger Joern , Pflügler Yvonne , Ruedinger Bernd
Published: September 2009

Glasses from the system MO (M=Mg, Ca)-Al2O3-BaO-SiO2-B2O3 were developed and evaluated as SOFC sealants. The glasses presented in this study are analysed by dilatometry, differential thermal analysis (DTA), hot-stage microscopy and high temperature x-ray diffraction. Microanalysis of the glass to metal interfaces is done by high resolution scanning electron microscopy (SEM). The materials presented in this paper show a good thermal expansion match with metallic interconnect materials, especially the glass with the code G018-305 has an excellent match with Crofer22H between the glass transition temperature Tg and room temperature. The developed glass ceramic composites have a high remaining residual glass phase of 60 wt.% compared to 40wt.% crystals, which primarily consist of Ba4Si6O16-silicates.
Induction Brazing for Gas Sealing and Joint Properties of Anode Supported Solid Oxide Fuel Cells
Authors: Heo Yeon-Hyuk , Lee Seung-Bok , Lim Tak-Hyung , Song Rak-Hyun , Shin Dong-Ryul
Published: September 2009

The nickel based brazing alloys (BNi 2, BNi 4) modified by reactive TiH2 have been studied for gas sealing properties of anode-supported tubular SOFCs to ferritic stainless steel by induction brazing process. BNi 2 and BNi 4 is not wetted in YSZ electrolyte, but the brazing alloy with added TiH2 showed good wettability with YSZ electrolyte due to formation of TiOx layer which has lower interfacial energy () than interfacial energy of Ni and YSZ. Among the tested brazing alloys (BNi 2, BNi 4, modified BNi 2, modified BNi 4), the others except for modified BNi 4 were not joined with YSZ. The modified BNi 4 showed the average value of 19 MPa and also the lowest gas leak rate of 8.0 × 10-7 L•cm-2sec-1 at pressure difference of 3 atm measured with He gas.
New Type of Current Collectors with Modified Near-surface Layer
Authors: Ledukhovskaya Nataliya , Frolova Elena , Strukov Gennady , Matveev Danila , Bredikhin Sergey I.
Published: September 2009

One challenge for advancing solid oxide fuel cell (SOFC) technology is to develop interconnect materials with adequate conductivity and stability for efficient long-term use. Proposed here is a technology for effectively modifying the surface of SOFC current collectors and significantly reducing the oxidation rate of ferritic stainless steel at elevated temperatures and high current densities. The formation of "Kirkendall voids" at the Crofer 22 APU ferritic stainless steel-intermetallic compound interface was observed and investigated. The Kirkendall voids play the role of a barrier layer blocking Cr diffusion to the surface and suppressing the formation of the resistive Cr2O3 surface layer. Long-term test measurements showed that the ASR value of the current collector-LSM junction decreases two times during the first 3000 hours and subsequently remains constant.
Constrained Sintering of Zirconia Films
Authors: Atkinson Alan , Kim Junk-Sik , Rudkin Robert , Taub Samuel , Wang Xin
Published: September 2009

In some planar SOFCs a thin film electrolyte is sintered onto a "rigid" substrate which constrains the film so that it can shrink only in one dimension, i.e. perpendicular to the substrate. The resulting stress and its effects on sintering kinetics and microstructure have been measured for screen printed YSZ films. The stress is in the range 0.5 to 3 MPa, depending on sintering temperature. The constraint slows the densification rate dramatically and results in porous defects that can compromise the gas-tightness of an electrolyte film.
Investigation of Electrical and Mechanical Properties of Tetragonal/Cubic Composite Electrolytes Prepared by Impregnation of 8YSZ with Zirconia Solution
Authors: Ghatee Mojtaba , Shariat Mohammad Hossain , Irvine John
Published: September 2009

Zirconia solid electrolytes with nonequilibrium composite structure were prepared by impregnation of a porous 8YSZ matrix with a solution of Zirconia. Microstructures were characterized by XRD and SEM. The electrical properties were studied by impedance spectroscopy as a function of temperature. Biaxial flexural strength and fracture toughness of composite samples were measured by ring on ring and Vickers microhardness indentation methods respectively. The microstructures of the composite electrolytes were composed of cubic grains surrounded by tetragonal second phase grains. It was shown that the electrical and mechanical properties of the prepared electrolyte can be adjusted by controlling the amount of doped zirconia. Increasing the amount of doped zirconia increases the tetragonal phase content which improves fracture toughness and fracture strength. In addition, increasing tetragonal phase content of the composite electrolytes decreases the conductivity at high temperatures while the situation is reversed at low temperatures.
Phase Transformation in Spray Pyrolysis Yttria-stabilized Zirconia Thin Films
Authors: Scherrer Barbara , Rupp Jennifer L. , Bieberle-Hutter Anja , Gauckler Ludwig J.
Published: September 2009

The phase transformation of yttria-stabilized zirconia (ZrO2)0.92(Y2O3)0.08 (8YSZ) thin films used as an electrolyte layer in micro-solid oxide fuel cells (µ-SOFCs) is investigated. Amorphous 8YSZ thin films are deposited by spray pyrolysis and their crystal symmetry, phase transformation and pore formation during heat treatment are analyzed. Both, microstructure and phase transformation can affect the thin film properties such as electrical conductivity and therefore the overall performance of the µ-SOFC.
Oxygen Mobility under Mechanical Stress
Authors: Araki Wakako , Arai Yoshio
Published: September 2009

In the present study, mobility of oxygen ions in yttria-stabilized zirconia under various stress conditions was examined by means of molecular dynamics (MD) simulation. The MD model was prepared allowing for the property anisotropy. A significant increase in the diffusion coefficient is obtained under a small tensile stress.
Heterogeneous Zirconia-based Solid Electrolytes Obtained by Sintering TZP+YSZ Powder Mixtures
Authors: Fernandes Cristina , Cunto Gabriel , Figueiredo Filipe , Frade Jorge R.
Published: September 2009

Powder mixtures of 3%Y2O3 (3Y) and 8%Y2O3 (8Y) were used to obtain heterogeneous solid electrolytes with good sinterability and mostly fine grain sizes, without significantly undue effects on ionic conductivity. Samples with 8Y:3Y{less than or equal to}1:1 retain submicrometer grain sizes, with very rare grains above 1 {less than or equal to}m. Impedance spectroscopy was used to de-convolute the bulk and grain boundary contributions, and to analyze their dependence on the fraction of 3Y. Bulk conductivity and its activation energy vary gradually with increasing 8Y:3Y ratio. The lower grain boundary conductivity of homogeneous 3Y can be ascribed to a combination of finer grain sizes and also lower specific grain boundary conductivity. However, the grain boundary conductivity differences of heterogeneous samples obtained from 3Y+8Y mixtures can be mainly ascribed to differences in grain size. Specific grain boundary conductivity results of these heterogeneous solid electrolytes are similar to those obtained for homogeneous 8Y.
Sintering Mechanisms of Cobalt-Doped Ceria and Zirconia Electrolytes in Intermediate-Temperature Solid Oxide Fuel Cells
Authors: Mori Masashi , Wang Zhenwei , Itoh Takanori
Published: September 2009

Ce0.9Gd0.1O1.95 (CGO) and Zr0.79Sc0.2Ce0.01O1.9 (ScSZ) have been proposed as possible alternative electrolytes in intermediatetemperature solid oxide fuel cells (SOFCs). In this study, the mechanisms of densely sintering Co-doped CGO and ScSZ electrolytes during the SOFC fabrication process were investigated using synchrotron X-ray diffraction (SR-XRD) analysis. The addition of CoO enhanced the sintering characteristics of both CGO and ScSZ. Based on the results of SR-XRD analysis, it was found that CGO and CoO did not form a solid solution after heat treatment at 1100{degree sign}C for 10 h. On the other hand, the solubility limit of Co in ScSZ was estimated to be {less than or equal to} 3 mol % after firing at 1200{degree sign}C, and Co-doping accelerated the conversion of the two phases of the fluorite structure into a single cubic phase. The diffusion of Co into ScSZ is thought to assist the densification through reaction sintering.
Bulk and Grain Boundary Conductivities as Function of Temperature and Oxygen Partial Pressure of Scandia-Stabilized Zirconia Co-Doped with Yttria and Ceria
Authors: Preis Wolfgang , Egger Andreas , Waldhäusl Jörg , Sitte Werner , De Carvalho Eduarda , Irvine John
Published: September 2009

The electrical properties of bulk and grain boundaries of CexY0.2-xSc0.6Zr3.2O8-d (0 < x < 0.2) have been investigated as a function of temperature and oxygen partial pressure by application of impedance spectroscopy. All samples have been prepared by means of a sol-gel combustion process. The ionic conductivities of the bulk are in the range from 0.03 to 0.04 S cm-1 at 700{degree sign}C in air. In the case of ceria-doped samples a significant decrease of the ionic conductivities of both bulk and grain boundary regions is observed under reducing conditions [p(O2) < 1E-15 bar, 700{degree sign}C] which may be interpreted in terms of association or clustering of oxygen vacancies. In addition, ageing studies have been performed on scandia-stabilized zirconia, doped with 10 mol% Sc2O3 and 1.0 mol% CeO2, in reducing atmosphere (1%-H2/Ar) at 700{degree sign}C by application of a dc four-point technique according to van der Pauw and ac measurements.
Sol-Gel Process to Prepare an Anode Supported YSZ Electrolyte
Authors: Courtin Emilie , Boy Philippe , Bianchi Luc , Poirot Nathalie , Laberty-Robert Christel
Published: September 2009

Several approaches based on the sol-gel process have been developed to synthesize YSZ (ZrO2-8%Y2O3) films with controlled porosities and thickness. Thick monolayer (> 10 µm) was obtained from a powder charged polymeric sol using the dip-coating process. This film exhibited porosities after a heat treatment at 1300{degree sign}C during 4 hours in air. These porosities are related to the decomposition of carbonate species formed during the heat-treatment. Dense films with a thickness ranging from 1 to 5 μm were synthesized via the deposition (spin-coating and dip-coating) of a solution containing YSZ nanoparticles. The calcinations temperature influences the films' density and porosity. YSZ films were synthesized on anode support (Ni-YSZ/YSZ) in order to evaluate the microstructure of these films in real fuel cell.
Effect of La2O3 Doping on Conductivity in the ZrO2 - Sc2O3 - CeO2 System
Authors: Barbashov Vladimir I. , Timchenko Vladimir M. , Nesova Elizaveta V.
Published: September 2009

The effect of La doping on conductivity of ZrO2 - Sc2O3 - CeO2 system was studied. The presence of the hysteresis loop was showed and connected with the polymorphic transformation from the ortorhombohedral phase to the cubic phase. 0,5 mol. % La2O3 doping replaces the hysteresis loop in a region of high temperatures. The received results is discussed in borders of the baric model for the ionic conductivity of zirconium oxide which assumes the control character for the influence of the hydrostatic pressure on the diffusion mobility of oxygen ions.
Modified Sol-gel Method used for Obtaining SOFC Electrolyte Materials
Authors: Suciu Crina Silvia , Erichsen Egil Severin , Hoffmann Alex C. , Dorolti Eugen , Tetean Romulus
Published: September 2009

A new modified sol-gel method using sucrose and pectin as organic precursors was used to obtain 7ScSZ and 11ScSZ nanoparticles as electrolyte materials for solid oxide fuel cells (SOFCs). Scandia stabilized zirconia (ScSZ) offers significantly higher conductivity than most other electrolyte materials (e.g. yttria stabilized zirconia, YSZ). The high cost of scandia can be compensated to some degree by the use of thin electrolyte films. Also, it is important to reduce the costs incurred by all the intermediate fabrication steps of SOFCs. The new organic precursors used in the modified sol-gel method have the advantages of being ubiquitous, cheap, easy to handle and store and environmentally friendly. The produced nano-powders were pressed to pellets and sintered in two different ways to obtain different grain sizes. The powders and pellets were investigated using TEM (Transmission Electron Microscopy), XRD (X-ray Diffraction), physical adsorption (BET), and EIS (Electrochemical Impedance Spectroscopy) to determine the morphology, particle size, crystal structure, crystallite size and specific surface area of the powders and the electrical properties of the sintered pellets.
High-Temperature Defect and Crystal Structure of Perovskite Type Oxide Ion Conductor La0.8Sr0.2Ga0.8Mg0.15Co0.05O3-δ
Authors: Nakayama Shota , Hashimoto Shin-ichi , Sato Kazuhisa , Yashiro Keiji , Amezawa Koji , Mizusaki Junichiro
Published: September 2009

A series of doped LaGaO3 perovskite type oxides is considered as the electrolyte of solid oxide fuel cells (SOFCs), due to their high oxide ionic conductivity. However, detailed defect chemistry, particularly the relationship between oxygen nonstoichiometry and lattice parameter under operating condition of SOFCs has not been understood well so far. To clarify the relationship, measurement was made on the oxygen nonstoichiometry of La0.8Sr0.2Ga0.8Mg0.15Co0.05O3-d by high temperature gravimetry, and on the crystal structure by in-situ high temperature XRD. Oxygen vacancy concentration increases with decrease in log (P(O2)) and increase in temperature, finally converging on 3-d=2.80. The large variation in the oxygen nonstoichiometry results from valence change of Co. The valence of Co at 3-d=2.80 is nearly +2.0, whereas, the valence of Co at 3-d=2.85 is considered close to +4.0. In-situ high temperature XRD confirmed that the oxygen vacancy formation led to increase in the lattice parameter, namely chemical expansion induced by oxygen nonstoichiometry.
Cation-deficient and Alkali Earth Cation-doped Solid Solutions La1-xMxGa1-yMgyO3-δ (M=VLa, Ca, Sr, Ba) Prepared by Different Techniques
Authors: Mateyshina Yulia G. , Uvarov Nikolai
Published: September 2009

Solid solutions La1-xMxGa1-yMgO3-δ.(M = VLa, Ca, Sr, Ba.).with perovskite structure were prepared by ceramic technology, mechanosynthesis, citrate synthesis and modified mechanochemical technique. The samples were characterized by XRD, chemical analysis, electrical measurements and impedance spectroscopy. The introduction of cationic vacancies the lanthanum gallate structure was demonstrated to be an effective way to obtain solid electrolytes with high ionic conductivity.
Electrical Characterization of LSGM Electrolytes Synthesized via Co-precipitation Route
Authors: Latorrata Saverio , Zampori Luca , Pelosato Renato , Dotelli Giovanni , Cristiani Cinzia , Ruffo Riccardo
Published: September 2009

The investigation of the role of La1-xSrxGa1-yMgyO3-δ (LSGM) structure and secondary phases on the total conductivity of three different samples, prepared via coprecipitation route in aqueos medium, starting from carbonate precursors, is here reported. Three different samples were prepared in order to evaluate different operating conditions on sample composition and structure. All of them were characterized by XRD, SEM, TG-DTA, FT-IR in order to investigate their structure, and by impedance spectroscopy (IS) to obtain information on their electrical properties. Samples C1 and C2 can be treated as conductor-insulator composites, while the interpretation of the low temperature impedance spectra of C3 is not straightforward.
Investigation on Crystal Structure and Oxide Ionic Conduction Path of LaGaO3-Based Oxide by in situ TOF Neutron Diffraction
Authors: Kitamura Naoto , Sugiyama Tomomaza , Idemoto Yasushi , Itoh Takanori
Published: September 2009

We focused on La0.8Sr0.2Ga0.8Mg0.2O3-d (LSGM) and La0.8Sr0.2Ga0.8Mg0.115Co0.085O3-d (LSGMC) with the perovskite structure as an electrolyte for solid oxide fuel cell, and investigated their crystal structures at elevated temperature by Rietveld technique using their neutron diffractions. As a result, it was indicated that the materials had a single phase of an orthorhombic structure (S. G.; Pnma) at the temperature range from 680 to 1073 K, regardless of the substituent cation species. Anisotropies of atomic displacement parameters of the oxygens, however, were supposed to be different between LSGM and LSGMC. Such a difference in the oxygen's behavior suggests different oxide-ion migration routes among the materials, and this may be one of the reasons why LSGMC shows higher oxide-ion conductivity than LSGM.
Two-step Synthesis of Yttrium-doped Barium Zirconate Protonic Conductors
Authors: Oliveira Olavo , Andrade Tiago , Muccillo Eliana N. , Berton Marco , Garcia Carlos , Muccillo Reginaldo
Published: September 2009

Yttrium-doped barium zirconate protonic conductors were synthesized by a two-step route consisting on diffusing barium ions into previously prepared yttrium-doped zirconia. The evolution of the structural phase content was followed by in situ high temperature X-ray diffraction in the room temperature-1200C and by X-ray diffraction analysis of a mixture of cubic yttria-stabilized zirconia and barium carbonate heat treated at high temperatures. The attainment of the BaZr0.85Y0.15O3-delta composition was evaluated by X-ray fluorescence measurements. Pellets sintered at 1500C had the electrical behavior under humidified argon studied by impedance spectroscopy in the 300-600C in the 40 Hz-110 MHz frequency range. Unitary planar solid oxide fuel cells La0,6Sr0,4Fe0,8Co0,2O3/BaZr0.85Y0.15O3-delta/Pt were assembled for measuring the output voltage under operation with hydrogen, methane and ethanol as fuels and air as the oxidant.
Comparison of Structural and Electrical Properties of Strontium Zirconate Pellets and Thin Films
Authors: Arab Pour Yazdi Mohammad , Briois Pascal , Georges Samuel , Shaula Aliaksandr , Cavaleiro Albano , Billard Alain
Published: September 2009

In this study, SrZr0,84Y0,16O3-α (SZY16) coatings and pellets were synthesized by co-sputtering and solid state reaction, respectively, in order to compare their structural and electrical properties. The SZY16 as deposited coatings are amorphous and must be annealed at 623 K to crystallize in the convenient SrZrO3 perovskite structure. After annealing, the grain size of the coatings is about half that of the sintered pellets. SEM analysis shows that both pellets and coatings remain stable after several heating cycles. Activation energies of the total electrical conductivity are 0.68 eV for both the film and the pellet. Nyquist diagrams show that the pellet yields two contributions whereas only one can be detected for the film, attributed to interfacial processes. Finally, the conductivity of the film is about one order of magnitude lower than that of the corresponding bulk pellet.
Electrical Transport and Electric Power Generation Properties of Lanthanum Silicate Oxyapatite Ceramics Prepared by a Sol-gel Method
Authors: Kobayashi Kiyoshi , Nishimura Chikashi
Published: September 2009

Dense ceramics of lanthanum silicate oxyapatite with composition of La9.50(SiO4)6O2.25 were fabricated from a precursor prepared by a water-based sol-gel method and sintered at 1773 K; this temperature is considerably lower than the sintering temperature used in conventional solid-state reaction method. The electrical transport properties and solid oxide fuel cell(SOFC) performance of lanthanum silicate oxyapatite ceramics were investigated by measuring the total conductivity, electromotive force of an oxygen concentration cell, and SOFC performance test. The transference number of oxide ions was found to be unity between 773 K and 1273 K under oxygen partial pressures from 10-25 atm to 1 atm. An almost linear relationship was observed between the output current and the terminal voltage by the SOFC performance test.
Structure and Transport Properties of Doped Apatite-type Lanthanum Silicates Prepared via Mechanochemical Route
Authors: Kharlamova Tamara , Pavlova Svetlana , Sadykov Vladislav A. , Bespalko Yulia , Krieger Tamara , Lapina Olga , Khabibulin Dzhalil , Muzykantov Vitalii , Chaikina Marina , Uvarov Nikolai , Pavlukhin Yurii , Kriventsov Vladimir , Petrov Sergei , Argirusis Christos , Kaichev Vasilii
Published: September 2009

Structural features of Fe- and Al-doped apatite-type lanthanum silicates with different stoichiometry have been studied by using XRD, XPS, IR, UV-Vis, EXAFS, Mossbauer, 29Si and 27Al MAS NMR spectroscopy. The transport properties of the samples were also characterized by using impedance spectroscopy and oxygen isotope heteroexchange.
Effect of Microstructure on performance for Solid Oxide Fuel Cells of Ni-ScSZ Cermet Anode
Authors: Miyazaki Masato , Sasaki Kazuya , Suzuki Akihiro , Terai Takayuki
Published: September 2009

Conductivities of electron and oxide ion in the microstructure-controlled anode electrode measured as basic data to conduct a simulation to clarify the ideal microstructure of an anode electrode for internal reforming low temperature operating Solid oxide fuel cells are investigated. Microstructure of the anode, such as Ni and ScSZ particle diameters, pore diameters, and porosity, are controlled by adjusting a sintering temperature and adding an appropriate pore former particle. Electron resistivity and oxide ion resistivity were measured by four probe method and AC impedance method, respectively. Effects of microstructure on grain boundary resistivity and bulk resistivity were discussed separately.
Quantitative Evaluation of Transport Properties of SOFC Porous Anode by Random Walk Process
Authors: Kishimoto Masashi , Iwai Hiroshi , Saito Motohiro , Yoshida Hideo
Published: September 2009

Microstructural properties of an SOFC anode, such as tortuosity, surface-to-volume ratio and permeability, are quantitatively evaluated using three-dimensional data obtained by a system consisting of a focused ion beam and scanning electron microscope, FIB-SEM. A method employed to evaluate these properties is based on a random walk process in which the diffusion of imaginary particles is considered. In addition, the connectivities of three phases, i.e., the Ni, YSZ and pore phases are also analyzed. The relationships among these properties and their effects on transport phenomena in a porous anode are discussed. It is revealed that the low connectivity and complex microstructural configuration of the porous anode result in large tortuosities in the Ni and YSZ phases, respectively.
Electrochemical Behavior of Ni-CZO Cermet Anodes Prepared by Glycine-nitrate-process
Authors: Hari Prasad Dasari , Kim Hae-Ryoung , Park Jong-Sung , Lee Hae-Weon , Lee Jong-Ho
Published: September 2009

The impact of H2O for H2 oxidation on Ni-Ce0.75Zr0.25O2 (Ni-CZO) anode material synthesized by glycine-nitrate-process has been successfully investigated under dry and wet H2 fuel atmospheres over a range of operating conditions using yttria-stabilized zirconia (YSZ) electrolytes. Using electrochemical impedance spectroscopy (EIS), the polarization resistance (comprised of high frequency (HF) and low frequency (LF) features) of Ni-CZO symmetrical cells (Ni-CZO/YSZ/Ni-CZO) has been studied. The LF arc was almost negligible at all the operating temperatures in wet condition, and the HF arc was linearly increased with time at 800oC only in dry condition. The EIS response in dry and wet H2 conditions clearly exhibited that, water vapor enhanced the dissociative adsorption and surface diffusion of hydrogen and achieved the stable electrochemical performance at 3PB on the Ni-CZO cermet.
Methane Internal Reforming over Ni1-x-yCuxMgyO-SDC Anode Material at Intermediate Temperatures
Authors: Phongaksorn Monrudee , Ismail Mazni , Croiset Eric , Corbin Stephen , Yoo Yeong
Published: September 2009

The overall goal of this work is to develop a coking resistant Ni1-x-yCuxMgyO-SDC anode for IT-SOFCs. The Ni1-x-yCuxMgyO samples were prepared using 1) a one-step co-precipitation method and 2) a two-step co-precipitation/impregnation method. For the first method, Ni1-x-yCuxMgyO is synthesized via co-precipitation of Ni, Mg and Cu. In the two-step method, Ni0.9Mg0.1O is first prepared by co-precipitation of Ni and Mg, followed by addition of copper by impregnation. The materials were characterized using XRD, BET, TPO, and TPR. The activities toward methane steam reforming(MSR) were tested in a fixed-bed reactor. For the materials prepared from the one-step method, the MSR activity decreased when increasing Cu content even with only 5% Cu. With the two-step method, the MSR activity was not affected by the presence of Cu for concentration up to 5%. However, above 5% Cu the activity started to decrease. It was concluded that the two-step method is more effective.
In situ Reduction and Oxidation of Nickel from Solid Oxide Fuel Cells in a Transmission Electron Microscope
Authors: Faes Antonin , Jeangros Quentin , Wagner Jakob B. , Hansen Thomas W. , Van Herle Jan , Brisse Annabelle , Dunin-Borkowski Rafal , Hessler-Wyser Aïcha
Published: September 2009

Environmental transmission electron microscopy was used to characterize in situ the reduction and oxidation of nickel from a Ni/YSZ solid oxide fuel cell anode support between 300-500{degree sign}C. The reduction is done under low hydrogen pressure. The reduction initiates at the NiO/YSZ interface, then moves to the center of the NiO grain. At higher temperature the reduction occurs also at the free NiO surface and the NiO/NiO grain boundaries. The growth of Ni is epitaxial on its oxide. Due to high volume decrease, nanopores are formed during reduction. During oxidation, oxide nanocrystallites are formed on the nickel surface. The crystallites fill up the nickel porosity and create an inhomogeneous structure with remaining voids. This change in structure causes the nickel oxide to expand during a RedOx cycle.
Effect of Doping Elements on the Redox Kinetics of NiO-YSZ Powders for SOFC Applications
Authors: Contino Anna Rita , Cologna Marco , Modena Stefano , Sglavo Vincenzo M.
Published: September 2009

In the present work the effect of different amounts of Al and Ce oxides on reduction and oxidation kinetics of NiO/YSZ powders was investigated by thermogravimetric analysis at 800{degree sign}C in H2/Ar (reduction) or air (oxidation) atmosphere associated with detailed microstructural investigation of the samples. Both doping elements increase the reduction and oxidation rates. The reduction rate increases monotonically with Al amount while only when high Ce loads are used the first reduction rate is affected sensibly. The second reduction and re-oxidation are faster than the first one. The presence of coarser NiO particles generated in the first cycle and a consequent porosity modification can explains the generalized reaction rate increase.
Performance and Long-term Durability of Nanostructured Ni Anodes Doped with Transition Metals prepared by Spray Mist Dryer
Authors: Araki Kenta , Yamamoto Junya , Shiratori Yusuke , Ito Kohei , Sasaki Kazunari
Published: September 2009

Various additives for Ni anodes mixed with ScSZ prepared by spray mist dryer are examined for SOFCs in order to improve their anodic activity and long-term durability. Among the additives examined, it is found that the addition of Mn was highly effective to improve anode activity and sulfur tolerance. In case 5 mol% Mn was added to Ni, at 800 oC and 200 mA/cm2 for 50 % pre-reformed CH4 fuels (S/C = 2.5), the initial cell voltage drop by 5 ppm H2S was ca. 30 mV, which was less than half of the initial cell voltage drop for undoped Ni-cermet anodes. Mn-oxide reacts with NiO during preparation, while Ni metal nanoparticles will be segregated after reduction and Mn-oxide acts as pinning sites to depress grain growth and agglomeration of Ni particles, leading to lower anodic overvoltage and higher sulfur tolerance. Long-term durability up to 3000 hours has been verified.