bluuebunny/crossref_metadata_2025 huggingface dataset:
Production of Compliant Current Collector-Supported Micro-Tubular Solid Oxide Fuel Cells
Authors: De La Torre Ricardo , Casarin Michele , Sglavo Vincenzo M.
Published: April 2011

An innovative current collection method for micro-tubular solid oxide fuel cells (SOFCs) was proposed in the present work. Pencil lead was used as support for the coiled current-collector during processing and as sacrificial inner core for the fabrication of micro-tubular SOFCs. A nickel wire was coiled around the pencil lead thus producing a compliant and homogeneously distributed current collector along the cell length and with two terminals available for the electrical connections. The cell consists of NiO/YSZ anode, YSZ electrolyte and LSM cathode sequentially deposited by dip coating around the Ni current collector. I-V curves showed maximum power output of ~190 mW/cm2 at 800ºC under wet H2 fuel flow in cells with ~1.2 mm diameter and 30 mm length with an active cathode area of about 0.75 cm2.
Investigations on Single Chamber Solid Oxide Fuel Cells: From Single Cell to Micro-Stack
Authors: Lü Zhe , Wei Bo , Liu Mingliang , Wang Zhihong , Tian Yanting , Su Wenhui
Published: April 2011

In this paper, some investigation results of our research group about single chamber solid oxide fuel cells including single cells and micro-stacks are presented. On single cell investigations, both electrolyte-supported (ES) and anode- supported (AS) membrane ones were studied. The primary work focused on reducing the inner resistance, improving the open circuit voltage (OCV) as well as power density, and enhancing the operation stability. On 2-cell short stacks, our investigation focused on AS type stacks with different configurations and the structure parameter effect. To develop useful SC-SOFC system, more stack configurations have been designed and tested. Many efforts have been made to optimize the gas flow field of multi-cell micro-stacks in order to enhance the OCV, power output and fuel utilization. Configurations of SC-SOFC stacks, including star-type, array type and micro-stack with root gas tubes have been designed and tested successfully.
Modeling of a SOFC Fuelled by Methane: Influence of the Methane Steam Reforming Kinetics
Authors: Girona Kelly , Toyir Jamil , Gélin Patrick , Bultel Yann
Published: April 2011

Methane appears to be a fuel of great interest for SOFC systems because it can be directly converted into hydrogen by Gradual Internal Reforming (GIR) within the SOFC anode with a new cell configuration. This study proposes a model of SOFC which takes into account the kinetics of the reforming reaction on the catalyst in order to assess the limitations under current of this new configuration of the SOFC cell.
A Near Triple-Phase Boundary Region Model for H2S Poisoning of SOFC Anodes
Authors: Monder Dayadeep S. , Karan Kunal
Published: April 2011

H2S concentrations in the fuel at the parts per million level are known to dramatically reduce the electrochemical performance of Ni-based anodes in solid oxide fuel cells. This study presents a transport-reaction model that describes the surface (electro)chemistry of H2 electro-oxidation in the presence of H2S on a Ni-YSZ patterned anode. By including the adsorption and dissociation of H2S on the Ni surface, this model is able to directly simulate the S poisoning of the anode. Simulations of the anode polarization curve with and without H2S in the fuel at different operating conditions are presented and discussed.
Three Dimensional Simulation of a Counter-Flow Planar Solid Oxide Fuel Cell
Authors: Mollayi Barzi Yaser , Raoufi Arman , Manafi Rasi Negar , Davari Susan
Published: April 2011

The following study investigates a 3-dimensional numerical model for the heat/mass and charge transfer simulation of a counter-flow planar solid oxide fuel cell to predict and evaluate its performance. The main emphasis in developing present model is to use for design and achieving optimized geometrical and effective parameters. This model can be used for calculation of thermal stresses and the structural design of the cell. Three dimensional transport equations are solved using computational fluid dynamics to simulate the flow field and to calculate species and temperature distribution in the computational domain. All ohmic, thermodynamic and electrochemical heat sources are taken in to account. Mass sources are calculated using the electrochemical reaction of hydrogen. Also the 3-D charge transfer equations are solved to predict the electrical potential distribution in the cell body and current collectors considering three kinds of polarization (ohmic, activation and concentration). To evaluate the model capabilities the results of the present study is compared with the experimental data and its accuracy is analyzed.
Numerical Approach of a Single-Chamber Solid Oxide Fuel Cell without Mixed Reactant Feeding
Authors: Ould Ahmedou Sid'Ahmed , Deseure Jonathan , Doche Olivier , Bultel Yann
Published: April 2011

Satisfactory power densities for Single Chamber Solid Oxide Fuel Cells (SC-SOFC) can be obtained with ceramic materials already used in dual chambers SOFC. In order to increase the oxygen access trough the cathode, the authors propose to combine a SC-SOFC and a dual chamber SOFC by using a porous ceramic membrane. In this computing work, species transport is governed by convection-diffusion equations in the gas channel and the porous media. In addition, momentum balances are solved using Brinkman formulation through the porous cell. Charge transfer occurs at the electrode/electrolyte interface and is described by the general Butler-Volmer equation. Simulations allow the calculation of the distributions of partial pressures for all the gas species within the cell (CH4, H2, CO, CO2, H2O, O2, N2). As expected, the injection of only 3% of the steam water increases the chemical conversion of methane.
Numerical Analysis on the Dynamic Behavior of a Solid Oxide Fuel Cell with a Multivariable Control Strategy
Authors: Komatsu Yosuke , Kimijima Shinji , Szmyd Janusz
Published: April 2011

The present paper discusses the operation of a solid oxide fuel cell (SOFC) system with a multivariable control scheme through dynamic simulation. The SOFC power output, operating temperature, fuel utilization factor and steam-to-carbon ratio (S/C) were employed as the controlled variables. The current density, air, fuel and steam flow rates were chosen for use in the SOFC control. Feedback control methodology was adopted to achieve adequate operation of the SOFC. The results from the conducted simulation show the capability of the multivariable control of SOFC operation. The temperature control scheme requires strict limitations on the air flow rate manipulation and the flexible adjustment of the reference value to system power output.
Solid Oxide Fuel Cell Electrode 3D Microstructure and Performance Modeling
Authors: Rhazaoui Khalil , Cai Qiong , Shearing Paul , Adjiman Claire , Brandon N.P.
Published: April 2011

A strong correlation exists between the performance of Solid Oxide Fuel Cells (SOFCs) and their electrode microstructures, requiring an improved understanding of this relationship if more effective application-specific SOFC electrodes are to be designed. A model has been developed capable of generating a random 3D electrode microstructure and predicting its performance by analyzing structure properties such as porosity, percolation of the various phases and the length and distribution of triple phase boundaries. A Monte Carlo process is used initially to randomly position spherical particles of the three different phases, in a packed bed. Next, the pore former particles are removed. The remaining particles are then expanded uniformly to represent the sintering process, resulting in a network of particles of ionic and electronic phases overlapping each other, creating a distinctive, examinable electrode. This paper presents the impact of a range of technologically important parameters such as particle size and sintering expansion coefficient on electrode performance.
Strain Effect on Oxygen Migration in Yttria-Stabilized Zirconia
Authors: Araki Wakako , Kuribara Masaya , Arai Yoshio
Published: April 2011

In the present study, the strain effect on the oxygen migration in the yttria-stabilized zirconia electrolyte has been investigated by means of the molecular dynamics simulation and the experiment. In both the simulation and the experiment, the oxygen migration is examined under uniaxial stress conditions. The result has indicated that the oxygen migration can be enhanced in the tensile direction whereas it can be decreased in the compressive direction. The strain works more effectively when it is applied in the <100> direction and also when the cubic structure is less stabilized, e.g., at lower temperature and with lower yttria concentration. The maximum improvement caused by the uniaxial tensile stress are about 40 % in the simulation, where the oxygen ions are largely displaced in the fluorite lattice structure.
Chemical Expansion and Frozen-In Oxygen Vacancies in Pr-Doped Ceria
Authors: Kuru Yener , Bishop Sean R. , Kim Jae-Jin , Yildiz Bilge , Tuller Harry L.
Published: April 2011

Doped CeO2 is a promising candidate for solid oxide fuel cell electrolyte and electrode applications because of its high ionic conductivity and reduction/oxidation behavior at intermediate temperatures. Its electronic and ionic properties and microstructural stability are of particular interest. The present study demonstrates that the large number of oxygen vacancies created in PrxCe1-xO2-δ (PCO) at elevated temperatures can be accommodated at room temperature if cooling is performed in relatively low oxygen partial pressures (i.e. P(O2) ~ 10-3 mbar). We use the temperature dependence of the chemical expansion in reduced PCO as a metric to explore this phenomenon.
Oxygen Diffusion in Ordered/Disordered Double Perovskites
Authors: Tarancón Albert , Chroneos Alexander , Parfitt David , Kilner John
Published: April 2011

Molecular Dynamics simulations of ordered and disordered versions of a gadolinium barium cobaltite have been performed for the temperature range between 800K and 1400K. Oxygen diffusivity for the ordered and disordered phase was compared resulting in an analysis of the effect of cationic ordering on the oxygen mass transport properties.
Phase Transformation of Stabilized Zirconia on SOFC Stacks
Authors: Kishimoto Haruo , Shimonosono Taro , Yamaji Katsuhiko , Brito Manuel E. , Horita Teruhisa , Yokokawa Harumi
Published: April 2011

The phase transformation of cubic stabilized zirconia in real SOFC stacks, especially in regions along the anode/electrolyte interface, was investigated by micro-Raman spectroscopy. In some real stacks, phase transformation of cubic stabilized zirconia into tetragonal phase was observed at the electrolyte/anode interface and/or in the anode after long time operation. On the other hand, in electrolyte, phase transformation was rarely observed. Bearing in mind the possible effect of Ni dissolution on phase transformation of zirconia, in parallel, a study was also carried out. NiO doped cubic zirconia was partially transformed into tetragonal phase, but transformation was not observed for cubic zirconia without NiO dissolution. It was clear that phase transformation was enhanced by NiO dissolution into the cubic stabilized zirconia.
The Influence of Sintering Time of Feedstock Powders on the Electrical Properties of La10(SiO4)6O3 Electrolyte Coatings
Authors: Gao Wei , Liao Hanlin , Coddet Christian
Published: April 2011

Electrical properties of apatite-type La10(SiO4)6O3 electrolyte coatings as a new class of the fast oxide ion conductors were investigated in this study. The feedstock powders were prepared by sintering the mixed oxide powders in different sintering times. The ceramic coatings with a typical composition of La10(SiO4)6O3 were deposited by atmospheric plasma spraying (APS). The highest conductivity of the dense composite electrolyte coatings reaches 6.8×10-6 S•cm-1 at 435 ºC in air which is comparable to other apatite-type lanthanum silicate (ATLS) conductors.
Soft Chemistry Routes for the Synthesis of Sr0.02La0.98Nb0.6Ta0.4O4 Proton Conductor
Authors: Santibáñez-Mendieta Alma B. , Fabbri Emiliana , Licoccia Silvia , Traversa Enrico
Published: April 2011

The Sr0.02La0.98Nb0.6Ta0.4O4 powder was successfully synthesized by auto-combustion and co-precipitation methods. For both methodologies the calcination conditions are 1100 °C for 10 hrs showing an improvement over the ones required for the solid state reaction method. The conductivity achieved by the pellets manufactured via the auto-combustion method was 2.2×10-4 S/cm at 800°C.
Synthesis and Properties of BaZr0.1Ce0.7Y02-xMxO3-δ (x = 0, 0.1; M = Dy, Yb) Compounds
Authors: Muccillo Reginaldo , Muccillo Eliana N.
Published: April 2011

The following barium cerate zirconate compounds were prepared by the solid state route: BaZr0.1Ce0.7Y0.2O3-δ, BaZr0.1Ce0.7Dy0.2O3-δ, BaZr0.1Ce0.7Y0.1Dy0.1O3-δ, The powders were attrition milled, pressed and sintered at 1550 °/4 h. X-ray diffraction data of all compositions show the perovskite orthorhombic phase (powders) and the perovskite cubic phase (pellets). Impedance spectroscopy measurements in the 5 Hz-13 MHz frequency range show that Dy may substitute total or partially for Y without noticeable change in the electrical conductivity, whereas the Yb substitution leads to a decrease in the electrical conductivity. The bulk electrical resistivity follows the trend: Yb- < Dy- < Dy-Y- < Yb-Y- < Y-doped barium cerate zirconate sintered ceramics. A detailed scanning probe microscopy analysis of the polished and thermally etched surfaces of the sintered pellets show images of sub-intergranular regions, which are further evidences of the large grain boundary electrical resistivity of barium cerate compounds.
Microwave-Assisted Preparation of Cu Coated Ni/YSZ Anode for Direct Utilization of Dry CH4 in SOFC
Authors: Islam Shamiul , Hill Josephine M.
Published: April 2011

Microwave irradiation was used to deposit Cu into a Ni/YSZ anode of an electrolyte-supported solid oxide fuel cell (SOFC). Irradiation times of 15 s and 60 s were used. The shorter time was sufficient to deposit 6 wt% Cu (with respect to Ni) from a solution of Cu(NO3)2 and ethylene glycol (HOCH2CH2OH) with average particle sizes of ~21 nm. Irradiation for 60 s resulted in a wider distribution of particle sizes up to 60 nm in size. The electrochemical performance of the microwave Cu-coated Ni/YSZ anodes was tested in dry H2 and dry CH4 at 1073 K, and their activities and stabilities were similar to that reported for Cu-Ni/YSZ/CeO2 anodes prepared by impregnation. That is, the presence of Cu reduced the extent and severity of carbon deposition.
Safe Operating Conditions to Prevent Damage in Ni-YSZ Anode Supported SOFC
Authors: Roche Virginie , Roux Claude , Steil Marlu Cesar
Published: April 2011

Re-oxidation of Ni-YSZ composite anodes was investigated by thermogravimetry and conductivity analyses. Cyclic expansion during redox cycles were also followed by dilatometry. Characterizations were performed under different oxygen pressures and temperatures with a special emphasis on 800°C and mixtures of 0.3, 5 and 20% O2 in N2 simulating an accidental fuel stop during SOFC operation. The re-oxidation kinetic was established. Measured mechanical deformations provide data on cumulated deformations and relevant aging. The experimental results allowed us to define a safety procedure to prevent anode deterioration.
Ab Initio Study of Activity and Coke-Tolerance of Ni/CeZrO2 Anodes of SOFC as a Function of Zirconia Concentration
Authors: Shishkin Maxim , Ziegler Tom
Published: April 2011

Appling ab initio DFT+U method, we show that addition of zirconia to the anode of SOFC, modeled by Ni/CexZr1-xO2 cermet results in a higher activity of the oxide surface as compared to both CeO2 and ZrO2 with zirconia concentration (x) up to 50%. Higher concentration of zirconia (from 50 to 100%) leads to the increase of the oxygen removal energy and lower activity of the oxide surface. We also show that addition of ZrO2 can result in the decrease of the oxygen spillover barrier from the oxide to Ni as compared to Ni/CeO2 system, which may explain the improved coke tolerance of the doped oxide. We point out that the minimal barrier of oxygen spillover occurs at concentration of zirconia of x∼25% in line with enhanced coke tolerance at this level of doping of cerium oxide observed experimentally in some previous works.
Kinetic Modeling of Nickel Oxidation in SOFC Anodes
Authors: Neidhardt Jonathan , Henke Moritz , Bessler Wolfgang G.
Published: April 2011

Understanding the mechanisms of performance degradation is of key importance for increasing the lifetime of solid oxide fuel cells (SOFC). The aim of this work is to achieve a deeper understanding of the processes leading to nickel oxidation at Ni/YSZ composite anodes. We present a kinetic model of chemical nickel oxidation which was integrated into a two-dimensional model of an anode-supported single cell. The feedback between nickel oxidation and cell performance was modeled by taking into account both, a loss in kinetic performance (via reducing three-phase boundary length) and a reduction in gas-phase diffusivity (via porosity decrease upon solid volume expansion). The simulations allow the quantification of nickel oxide formation over time and its influence on the cell performance.
Theoretical Study for the Sintering of Nickel Anode in Solid Oxide Fuel Cell
Authors: Nakao Kazuhide , Ogura Teppei , Ishimoto Takayoshi , Koyama Michihisa
Published: April 2011

Ni sintering is one of the main factors in SOFC degradation. In this study, we first investigated the surface orientation on Ni nanoparticles by using molecular dynamics (MD) method. It was identified that Ni nanoparticles mainly consists of four facets: (111), (100), (110), and (113). We also analyzed the stability of surface energy, which is dominant driving force of sintering phenomena, in various sizes of Ni nanoparticles. The MD simulation of two particles system was performed to investigate the sintering phenomena. We found that the diffusion coefficient is almost same at the temperature between 1373 and 1673 K, while contact surface orientation is different. It was indicated that dominant sintering mechanism of Ni nanopartisles is surface diffusion.
Electrochemical Oxidation at SOFC Anodes: Comparison of Patterned Nickel Anodes and Nickel/8YSZ Cermet Anodes
Authors: Utz Annika , Joos Jochen , Weber André , Ivers-Tiffée Ellen
Published: April 2011

Patterned Ni anodes are a common method to determine elementary kinetic reaction mechanism at the anode of Solid Oxide Fuel Cells. Their well defined Triple-Phase-Boundary (TPB) of electrode, electrolyte and gas phase, where the electrochemical oxidation takes place, is easily accessible. However, the direct transfer of knowledge gained with patterned Ni anodes to technical Ni/8YSZ cermet anodes is doubtful. For the first time a comparison of the electrochemical performance of both anode concepts is performed by means of (i) transmission line model calculations and (ii) performance simulations using a 3D FEM microstructure model. The good agreement observed between the performance of patterned Ni anodes and Ni/8YSZ cermet anodes indicates similar reaction mechanisms at the TPB of both anode concepts. Especially in H2-H2O atmosphere, the agreement of (i) absolute ASR values and (ii) parameter dependencies is very good and shows the applicability of patterned Ni anodes for the investigation of the electrochemistry of technical Ni/8YSZ cermet anodes.
Investigation of MgO Promoted NiO: SDC Anode Material for Intermediate Temperatures Solid Oxide Fuel Cells
Authors: Phongaksorn Monrudee , Yan Aiyu , Ismail Mazni , Ideris Asmida , Croiset Eric , Corbin Stephen , Yoo Yeong
Published: April 2011

This paper investigated the electrochemical performance of Ni0.9Mg0.1O-SDC for hydrogen and methane fuelled IT-SOFCs using an electrolyte-supported button cells. The Ni0.9Mg0.1O-SDC anode has been chosen based on the premises that the doped-ceria is suitable for intermediate temperatures (550-800°); that Ni is known as an active metal and good electron conductor; that MgO is a promoter to avoid agglomeration of Ni during reduction and to achieve higher Ni dispersion; and finally, that CeO2-Sm2O3 (SDC) improves oxide ion transport to the cell at this intermediate temperature range. Electrochemical performance under humidified hydrogen and methane were carried out at 650, 700 and 750° and tested using polarization curve and electrochemical impedance spectra. Adding MgO to NiO-SDC anode improved the maximum power density and lowered the polarization resistance of the cell.
Reaction Sites of Mixed Conductor Anodes in Solid Oxide Fuel Cells
Authors: Kikuchi Ryuji , Okamoto Takaaki , Akamatsu Kazuki , Sugawara Takashi , Nakao Shin-ichi
Published: April 2011

Pt pattern anodes with defined TPB length were prepared on the surface of YSZ or SDC (Samaria-doped ceria) interlayer deposited on an YSZ disk, in order to investigate the reaction sites of SOFC anodes consisting of mixed conductor oxides. The electrode resistance was measured by AC impedance method under different conditions and assigned to reaction resistances by fitting to an equivalent circuit. The dependence of the reaction resistances was investigated by varying operation temperature, hydrogen partial pressure, and the number of the Pt electrode patterns. The impedance in the Nyquist plots was fitted by two semicircles at low and high frequency, and the high frequency arc was assigned to the anodic reactions nearby the TPB. For the same TPB length, the conductivity determined from the high frequency arc for the Pt electrodes on the SDC layer was almost ten times as large as that on the YSZ layer.
Fuel Flexible Anode for Solid Oxide Fuel Cells: An Electrochemical and Catalytic Study
Authors: Lo Faro Massimiliano , Stassi Alessandro , Monforte Giuseppe , Minutoli Maurizio , Antonucci Vincenzo , Modafferi Vincenza , Frontera Patrizia , Busacca Concetta , Antonucci Pierluigi , Aricò Antonino Salvatore
Published: April 2011

A composite Ni-modified La0.6Sr0.4Fe0.8Co0.2O3 / Ce0.9Gd0.1O2 electrocatalyst was investigated for the autothermal reforming (ATR) of methanol, ethanol, glycerol and propane. The catalyst was also investigated as anode for the direct utilization of such dry fuels in solid oxide fuel cells (SOFCs) and the performance results achieved for the direct utilization of such fuels appear promising for SOFC application in remote and micro-distributed energy generation as well as for portable power sources.
Development, Fabrication and Testing of Perovskite-Based Anodes for Tubular Solid Oxide Fuel Cells
Authors: Babiniec Sean , Richards Amy E. , Faino Nicolaus , Sullivan Neal
Published: April 2011

This paper provides initial results for our development and analysis of perovskite-based anode materials, with comparisons made to more-conventional Ni-YSZ anodes. Experimental techniques include X-ray diffraction, scanning electron microscopy, DC-conductivity, gas-transport and internal-reforming chemistry, and open circuit voltage testing. Phase-stability during processing is demonstrated using XRD and SEM techniques. Internal reforming of the LSCM anode is found to be significantly lower than that of conventional Ni-YSZ materials. While the electronic conductivity of the perovskite anodes is also found to be significantly lower than Ni-YSZ, the conductivity of strontium-doped lanthanum titanate is found to be acceptable for SOFC operational requirements. Open circuit voltage of full cells with SLT-based cathodes is less than theoretical OCV; however, OCV is found to increase dramatically with cell temperature. This suggests that a catalyst may be necessary, and ceria catalyst impregnation techniques have been demonstrated. Results are used to guide design of future perovskite-based anodes.
Enhanced Performances of Ln2NiO4+δ / CGO Multilayered Anodes for High Temperature Steam Electrolysis (HTSE)
Authors: Ogier Tiphaine , Chauveau Florent , Bassat Jean-Marc , Mauvy Fabrice , Grenier Jean-Claude , Mougin Julie , Petitjean Marie
Published: April 2011

Multilayered oxygen electrodes for High Temperature Steam Electrolysis (HTSE) based on nickelate oxides Ln2NiO4+δ (Ln=La, Pr or Nd) as active material and gadolinium-doped ceria (CGO) as buffer layer have been characterized on symmetrical half-cells with yttria-stabilized zirconia (YSZ) as electrolyte. The polarization resistances (Rp) were measured by electrochemical impedance spectroscopy, between 600°C and 800°C. The Rp values of Pr2NiO4+δ/CGO multilayered electrodes are 3 times lower compared to those obtained with cells without CGO layer. At 800°C, Rp values of Ln2NiO4+δ/YSZ-based cells are about 0.14-0.20 Ω.cm² whereas the Rp of Pr2NiO4+δ/CGO/YSZ-based cell is reduced till 0.04 Ω.cm². Using a three-electrode setup, anodic overpotentials were obtained. Polarization curves evidence larger current densities for a given overpotential with cells containing the CGO interface. These results seem to show that multilayered materials based on nickelates Ln2NiO4+δ and CGO are particularly suitable for a use as oxygen electrode for HTSE.
Numerical Modeling of Nickel-Impregnated Porous YSZ-Supported Anodes and Comparison to Conventional Composite Ni-YSZ Electrodes
Authors: Hardjo Eric , Monder Dayadeep S. , Karan Kunal
Published: April 2011

SOFC anodes fabricated by Ni-impregnation of porous YSZ support have a microstructure distinct from the much studied/modeled conventional Ni-YSZ composite anodes. The Ni-infiltrated anode forms a semi-continuous network of electron conducting Ni-phase on the YSZ support framework. In this study, the Ni phase was modeled as a two-dimensional film on the porous YSZ structure and percolation theory was utilized to evaluate the following features that are unique to Ni-impregnated YSZ anodes - (i) the electrical conductivity of a semi-continuous film of nickel formed on the YSZ support framework, and (ii) the active TPBs in a nickel impregnated system based on the semi-continuous nature of the nickel phase. The effect of Ni loading relative to the total pore volume on electronic conductivities and TPB densities is evaluated and compared to literature.
Oxygen Nonstoichiometry of Perovskite-type La0.6Sr0.4Co1-yFeyO3-δ (y=0, 0.2, 0.4, 0.5, 0.6, 0.8, 1) SOFC Cathode Materials
Authors: Kuhn Melanie , Fukuda Yasuhiro , Hashimoto Shinichi , Sato Kazuhisa , Yashiro Keiji , Mizusaki Junichiro
Published: April 2011

The oxygen nonstoichiometry of La0.6Sr0.4Co1-yFeyO3-δ (LSCF) mixed-conducting perovskite-oxides can be classified into two groups: the cobalt-rich compounds (y=0, 0.2, 0.4) were previously reported to show a sharp decrease in oxygen content with reducing atmosphere, while the oxygen vacancy concentration increased more smoothly for the iron-rich compounds (y=0.6, 0.8, 1). Here we measured the oxygen content of LSCF with y=0.5 by thermogravimetry and coulometric titration as a function of oxygen partial pressure and temperature. No transitional behavior could be observed for La0.6Sr0.4Co0.5Fe0.5O3-δ, the oxygen nonstoichiometry showed the same behavior as for the cobalt-rich compounds. Except for y=1, the thermo-chemical stability of LSCF was little affected by the iron dopant content, all compounds (y=0-0.8) decomposed at similar oxygen partial pressures.
Electrical Conductivity and Oxygen Diffusivity of Perovskite-Type Solid Solution La0.6Sr0.4Co1-yFeyO3-δ (y=0.2, 0.4, 0.5, 0.6, 0.8)
Authors: Yashiro Keiji , Nakano Issei , Kuhn Melanie , Hashimoto Shinichi , Sato Kazuhisa , Mizusaki Junichiro
Published: April 2011

The electrical conductivity of La0.6Sr0.4Co1-yFeyO3-δ (y=0, 0.2, 0.4, 0.5, 0.6, 0.8, 1.0) were measured as a function of P(O2) and temperature. The conductivity variation can be well explained only by change in electron-hole concentration due to oxygen nonstoichiometry regardless of temperature. Conductivity relaxation analyses were also conducted to determine chemical diffusion coefficients by non-linear least squares fitting using the solution of Fick's diffusion equation. Oxygen vacancy diffusion coefficients were calculated using the chemical diffusion coefficients and oxygen nonstoichiometry. It should be emphasized that vacancy diffusion coefficients are not independent of oxygen vacancy concentration at lower temperature but steeply decrease with increase in oxygen vacancy concentration. These phenomena may cause the performance degradation of La0.6Sr0.4Co1-yFeyO3-δ cathode.
Systematic Studies of the Cathode-Electrolyte Interface in SOFC Cathodes Prepared by Infiltration
Authors: Küngas Rainer , Vohs John M. , Gorte Raymond J.
Published: April 2011

In this study, the effect of the morphology and ionic conductivity of the electrolyte material in SOFC composite cathodes is systematically studied. The specific surface area of porous yttria-stabilized zirconia (YSZ) scaffolds was varied by almost two orders of magnitude using different pore formers and surface treatment with hydrofluoric acid (HF). The effect of ionic conductivity on the performance of SOFC cathodes was studied for electrodes prepared by infiltration of 35 wt % LSF into 65% porous scandia-stabilized zirconia (ScSZ), YSZ, or yttria-alumina co-stabilized zirconia (YAZ) scaffolds of identical microstructure cathodes.
The Effects of Stress on the Defect and Electronic Properties of Mixed Ionic Electronic Conductors
Authors: Comets Olivier , Voorhees Peter W.
Published: April 2011

Understanding the effect of stress on the properties of oxides used in a solid oxide fuel cell (SOFC) is crucial for predicting its performance. The stress can come from many sources, such as compositional strain or thermal expansion mismatch between various constituents of the cell. These two effects can combine and alter the electronic structure as well as the defect chemistry of the oxide. In this paper, the effects of stress on the electron hole and oxygen vacancy concentrations and conductivities are addressed in mixed ionic electronic conductors (MIECs) in equilibrium with oxygen. Furthermore, two types of mixed conducting oxides are examined, and treated with the same formalism to illuminate the effects of stress on these materials. Applications of this model include SOFCs and thin films.
Strain Effects on Defect Chemistry in Epitaxial Perovskite Thin Films for Solid Oxide Fuel Cells
Authors: Gadre Milind , Lee Yueh-Lin , Swaminathan Narasimhan , Morgan Dane
Published: April 2011

The efficiency of Solid Oxide Fuel Cells depends strongly on the oxygen reduction reaction (ORR) rate on the cathode. Recent studies have suggested that large enhancements in defect thermokinetics and catalytic rates may be possible through use of epitaxially strained materials. Using ab-initio methods to simulate defect energetics under epitaxial strain, we quantify the effects of strain on oxygen stoichiometry in La{1-x}Sr{x}CoO{3-δ} (x=0.125) thin-films. We find at most a 2-3 fold increase in the vacancy concentration (at near 1000K) compared to bulk LSC over the range of strains from -2% (compressive) to about 4% (tensile). The results of this study suggest that epitaxial strain alone has a relatively weak effect of LSC oxygen vacancy concentration under SOFC conditions.
Ln(Sr,Ca)3(Fe,Co)3O10 Intergrowth Oxide Cathodes for Solid Oxide Fuel Cells
Authors: Kim Jung-hyun , Kim Young Nam , Lee Ki-Tae , Manthiram Arumugam
Published: April 2011

The perovskite-related intergrowth oxides Ln(Sr,Ca)3(Fe,Co)3O10, which belong to the n = 3 member of the Ruddlesden-Popper (R-P) series, have been explored as cathodes in solid oxide fuel cells (SOFC). The effects of cationic substitutions for Sr and Fe on the crystal chemistry, thermal properties, and electrochemical performances in SOFC have been investigated. The electrical conductivity, thermal expansion coefficient (TEC), and cathode performance increase with the substitution of Co for Fe. For instance, the LaSr3Fe3-xCoxO10 (LSFC) cathode composition shows electrochemical performances comparable to that of the well-known perovskite cathode La0.6Sr0.4CoO3. Further improvement in the cathode performance and a decrease in TEC have been realized by a substitution of less electropositive Ca for Sr in NdSr2.5Ca0.5Fe1.5Co1.5O10 (NSCFC). The improved performance of NSCFC is attributed to the decreased lattice distortion in the perovskite layer, which is beneficial to enhance the oxide-ion conductivity.
Development of Purification Methods of Rare Earth Compounds for Preparation of More Cost Effective Solid Oxide Fuel Cell Cathodes
Authors: Kanarbik Rait , Möller Priit , Kivi Indrek , Tamm Kadi , Lust Enn
Published: April 2011

Porous Pr1-xSrxCoO3-δ at Ce0.9Gd0.1O2-δ|Zr0.92Y0.08O2-δ electrolyte and Ni-Zr0.9Y0.1O2-δ supporting anode cells were prepared from the additionally purified Pr(NO3)3*6H2O. The Pr(NO3)3*6H2O was synthesized from Pr6O11, (obtained from AS Silmet) and was additionally purified using various solvent/solvent extraction methods. The inductively coupled plasma mass spectroscopy (ICP-MS) analysis showed the concentration of Cr cation lower than 0.01 ppm in the purified salts. The nitrate solution decomposition method was applied for the preparation of the cathodes under study. The single cells completed have been studied using cyclic voltammetry, electrochemical impedance and chrono amperometry methods. It was found that additionally purified Pr(NO3)3*6H2O can be used for the synthesis of cathodes for intermediate temperature solid oxide fuel cell single cells. Long-lasting time stability tests are under progress at the time being.
Microstructural Aspects of Cation Interdiffusion Across the LSCF/GDC Interface
Authors: Brito Manuel E. , Izuki Manabu , Yamaji Katsuhiko , Kishimoto Haruo , Shimonosono Taro , Horita Teruhisa , Yokokawa Harumi
Published: April 2011

To evaluate the long-term durability of a reaction barrier made of gadolinium doped ceria (GDC), we have measured cation diffusion in the LSCF/GDC system. Interdiffusion and microstructural evolution were investigated for samples annealed at temperatures of 1000 to 1200 oC and times from 30 to 672 h. Significant diffusion of lanthanum into GDC and diffusion of ceria and gadolinium into LSCF were observed. X-ray diffraction (XRD) revealed the formation of lanthanum doped ceria (LDC) in the vicinity of the interface. Furthermore, EDS analysis showed the uneven distribution of lanthanum into the polycrystalline ceria. Those compositional patched patterns are thought to be the result of the interplay of diffusion along grain boundaries and bulk diffusion, without excluding the possible effect of crystallographic relationship at the interface.
Preparation of Mesoporous La0.8Sr0.2MnO3 Infiltrated Coatings in Porous SOFC Cathodes Using Evaporation-Induced Self-Assembly Methods
Authors: Chao Robin , Kitchin John , Gerdes Kirk , Sabolsky Edward , Salvador Paul
Published: April 2011

We used evaporation-induced self-assembly (EISA) methods to infiltrate solid oxide fuel cell cathodes with La0.8Sr0.2MnO3. A single infiltration step using an EISA solution was found to generate thin catalyst coatings through the entire thicknesses of 75 - 750 μm thick porous media, including Y2O3 stabilized ZrO2 (YSZ), La0.8Sr0.2MnO3 (LSM), and La0.6Sr0.4Co0.2Fe0.8O3 (LSCF). After multiple infiltration and calcination steps, the LSM particles in LSCF cathodes of commercial button cells coated the pores as thin layers through the thickness with a slight increase in the concentration at the functional layer near the electrolyte / cathode boundary. The infiltrated La0.8Sr0.2MnO3 coatings were examined using transmission electron microscope (TEM) and were shown to be mesoporous, indicating that the nanostructure of electrocatalytic coatings can be tailored using this approach.
Comparison of X-ray Nanotomography and FIB-SEM in Quantifying the Composite LSM/YSZ SOFC Cathode Microstructure
Authors: Nelson George , Harris William , Lombardo Jeffrey , Izzo John , Chiu Wilson K. , Tanasini Pietro , Cantoni Marco , Van Herle Jan , Comninellis Christos , Andrews Joy , Liu Yijin , Pianetta Piero , Chu Yong
Published: April 2011

X-ray nanotomography and focused ion beam scanning electron microscopy (FIB-SEM) provide unique opportunities interrogate the 3D microstructure of solid oxide fuel cell (SOFC) electrodes with unprecedented spatial resolution with elemental specificity. Using x-ray nanotomography with differential absorption imaging across the Mn K-absorption edge (6539 eV), and energy selected backscatter detection for FIB-SEM, these two techniques have been applied to obtain 3D elemental mapping of the LSM, YSZ and pore phases in the cathode microstructure. Measurements taken by non-destructive x-ray imaging and FIB-SEM serial sectioning include three-phase boundary areas (nominal and effective); phase volume fraction; and phase contiguity. The results presented demonstrate the viability of nanotomography as a characterization technique and provide key insights into the SOFC cathode microstructure. The effects of instrument resolution on microstructural characterization are addressed and the roles of FIB-SEM and x-ray nanotomography in future SOFC microstructural characterization efforts are discussed.
Development of New Alloys for SOFC Interconnects with Excellent Oxidation Resistance and Reduced Cr-Evaporation
Authors: Yasuda Nobutaka , Uehara Toshihiro , Tanaka Shigenori , Yamamura Kazuhiro
Published: April 2011

Recently, metallic materials, especially Fe-Cr ferritic alloys (ex. ZMG232L), are promising as interconnect materials of solid oxide fuel cells (SOFCs) operated at around medium temperatures such as 700 - 850oC. As for these alloys, good oxidation resistance and good electrical conductivity in thin sheets are required. Moreover, it is needed to reduce Cr evaporation, which causes the degradation of the cell, from oxidized alloy surface. In this study, the effect of chemical compositions on required properties at elevated temperature was investigated and new alloys for SOFC Interconnects were developed.
On Potential Application of Coated Ferritic Stainless Steel Grades K41X and K44X in SOFC/HTE Interconnects
Authors: Santacreu Pierre O. , Girardon Pauline , Zahid Mohsine , Van Herle Jan , Hessler-Wyser Aïcha , Mougin Julie , Shemet Vladimir
Published: April 2011

The paper will present the high temperature properties of K41X and K44X ferritic alloys, in particular oxidation behavior in isothermal and cyclic conditions under operating atmosphere. The positive effect of the addition of a protective coating on these steel grades in terms of oxidation resistance will then be presented. Most of the studied coatings are Mn-Co spinels deposited by sol-gel, atmospheric plasma spray or electroplating, their aim being to limit the chromium evaporation and to fit the severe performance requirements. They lead to low and stable contact resistance, which is a requirement necessary for long-term SOFC/HTE operation: for example a contact resistance of 22 mΩ.cm2 was obtained after 3500h at 800°C in air with MnCoFe spinel coating. In this respect, K41X was recently chosen to be tested for the 3rd generation stacks of SOFC in the European project "REAL SOFC" or THE prototypes in French ANR projects
SOFC Module Material Development at Fuel Cell Energy
Authors: Huang Pengnian , Ghezel-Ayagh Hossein
Published: April 2011

FuelCell Energy (FCE) is engaged in the development of Solid Oxide Fuel Cell (SOFC) power plants under DOE's Solid State Conversion Alliance (SECA) Coal-Based Program. The ultimate goal of the project is to develop Multi-MW SOFC power plants suitable for integration with coal gasifiers and cable of capturing >90% of carbon in coal syngas. FCE is currently utilizing the SOFC stacks developed by Versa Power Systems (VPS) as building blocks for development of the sub-MW and MW scale fuel cell modules. The design of an SOFC stack module is comprised of an assembly of stack blocks to provide targeted dc power. Advanced materials are being developed for gas seals between stacks, mechanical and electrical connections of stack blocks, and thermal as well as electrical insulation within modules. This paper is a review of the progress in development of conducting module gasket (CMG), non-conducting gasket (PH) and electrical contacting paste materials.
Application of Biofuels to Solid Oxide Fuel Cell
Authors: Shiratori Yusuke , Tran Tuyen Quang , Takahashi Yutaro , Sasaki Kazunari
Published: April 2011

Performance of internal reforming SOFC was evaluated in the temperature range of 700-800oC for various biofuels. Three real biodiesel fuels (BDFs) and two pure fatty acid methyl esters (FAMEs) with different contents of unsaturated C-C bonds were fed directly to anode-supported SOFCs. The results demonstrated that in principle direct-feeding of BDFs into SOFC is viable, but the content of unsaturated FAMEs in BDF should be as lower as possible. Direct feeding of BDFs caused carbon deposition which was more significant at lower operational temperatures and at higher content of unsaturated FAMEs. On the other hand, biogas obtained by anaerobic fermentation of garbage, is suitable for SOFC operation because it contains natural reforming agent (CO2). Stable operation of internal reforming SOFC running on biogas was achieved by the addition of adequate amount of air to biogas.
In Situ Optical Studies of Solid Oxide Fuel Cells Operating With Dry and Humidified Oxygenated Fuels
Authors: Eigenbrodt Bryan , Kirtley John , Walker Robert A.
Published: April 2011

In situ Raman spectroscopy was used to investigate the real time chemistry occurring in solid oxide fuel cells (SOFCs) operating at 715åC with both dry and humidified ethanol. Electrochemical impedance spectroscopy (EIS) measurements were carried out concurrent with the optical studies to correlate changes in SOFC performance with the appearance of graphite on the anode surface. In cells operating with dry ethanol (diluted in Ar), graphite forms rapidly and the Ni/YSZ anode suffers irreversible structural degradation. With humidified ethanol, degradation is lessened in cells at OCV and can be completely suppressed in polarized cells. The tendency of ethanol to form graphite and the stability of the cermet anode is tied directly to the composition of the fuel mixture that reaches the anode. Ex situ FTIR analysis of the SOFC fuel effluent shows that dry ethanol experiences significant reforming, with CO, CH4, CO2, and C2H2 being the primary products.
Impurity Poisoning of SOFCs
Authors: Sasaki Kazunari , Haga Kengo , Yoshizumi Tomoo , Minematsu Daisuke , Yuki Eiji , Liu Run-Ru , Uryu Chie , Oshima Toshihiro , Taniguchi Shunsuke , Shiratori Yusuke , Ito Kohei
Published: April 2011

Long-term durability is one of the most important technological issues for SOFC system development. Life time of SOFCs can be critically affected by foreign species, including impurities and minor constituents in fuels and oxidants, from the raw materials of cell components, and from system components. This paper summarizes an effort to understand the impurity poisoning analyzed by adding specific impurity species into fuels under various operational conditions to clarify poisoning mechanisms and their concentration threshold. Possible acceleration procedures for poisoning phenomena have also been discussed.
Materials for Solid Oxide Electrolysis Cells
Authors: Elangovan S. , Hartvigsen Joseph , Larsen Dennis , Bay Insoo , Zhao Feng
Published: April 2011

High conversion efficiency of solid oxide electrolysis cells (SOEC) to electrolyze steam into hydrogen, and co-electrolyze steam-carbon dioxide mixture into syngas (i.e. synthesis gas composed of hydrogen and CO) provides the means to store electricity from renewable sources in chemical form. Performance stability of SOEC is critical in achieving a commercially viable system. While the materials that are used for solid oxide fuel cells (SOFC) are applicable to high temperature solid oxide electrolysis cells (SOEC), there are degradation mechanisms that are unique to SOEC mode of operation. Significant reduction in degradation rate has been achieved by the use of a new set of electrode materials and protective coatings on interconnects. The stability improvement however came at the expense of initial stack performance. The use of higher conductivity current distribution layer restored the high performance while maintaining the stability gain. An overview of materials evaluation work is presented.
High-Temperature CO2 and H2O Electrolysis with an Electrolyte-Supported Solid Oxide Cell
Authors: Fu Qingxi , Dailly Julian , Brisse Annabelle , Zahid Mohsine
Published: April 2011

High-temperature CO2 and H2O co-electrolysis using solid oxide cells can produce efficiently syngas that in turn can be converted to synfuel through technologically mature technologies like the Fischer-Tropsch (F-T) process. It can be used to convert renewable electrical energy to chemical energy stored in liquid fuels to support a sustainable transport in the future. In the present paper a commercial electrolyte-supported solid oxide cell has been operated under CO2/H2O-electrolysis conditions. It has been found that the product gas composition can be well predicted by assuming that the reverse water-gas shift (RWGS) reaction reaches a thermodynamic equilibrium. In comparison to wet CO2 electrolysis (CO2 with H2O or H2), the cell ASR is only slightly increased under dry CO2 electrolysis conditions, indicating that, besides the RWGS reaction, electrochemical reduction of CO2 could also play an important role for CO formation under CO2/H2O co-electrolysis conditions.
Electrochemical Analysis of Biogas Fueled Anode Supported SOFC
Authors: Leonide André , Weber André , Ivers-Tiffée Ellen
Published: April 2011

In this study the performance of anode supported solid oxide fuel cells (ASC) operated with biogas derived from corn silage (biogas) is analyzed. The fuel gas is produced by supercritical water gasification at the pilot plant VERENA operated at the Karlsruhe Institute of Technology. Current voltage characteristics show a slightly (6-14%) lower power density during biogas operation compared to hydrogen fuelled SOFC single cells. Impedance analysis reveals an increased activation polarization resistance and an additional polarization process at frequencies below 2 Hz during biogas operation. These two effects contribute to an overall higher polarization resistance of the biogas fueled ASC resulting in a lower power output.
Scaling Scheme and Performance Perspective of Cross-Current Tetrode (XCT) SOI MOSFET for Future Ultra-Low Power Applications
Authors: Omura Y. , Fukuchi Kyota , Ino Daishi , Hayashi Osanori
Published: April 2011

This paper introduces a scaling scheme of the cross-current tetrode (XCT) SOI MOSFET and preliminary results. It is demonstrated that the XCT-SOI MOSFET is a promising solution for future 'ultra low-energy' LSIs suitable for medical applications. It is shown that the proposed scaling scheme yields useful design guidelines for XCT devices.
Subband Structure Engineering in Silicon-On-Insulator FinFETs Using Confinement
Authors: Stanojevic Zlatan , Sverdlov Victor , Selberherr Siegfried
Published: April 2011

Splitting between equivalent valleys larger than the spin splitting energy is observed in confined electron systems, e.g. Si films grown either on SiGe substrate or Si dioxide and Si/SiGe quantum dots. Understanding the contribution of different factors in the valley degeneracy lifting is of key importance for the development of spin-based devices in Si. We demonstrate that the splitting between equivalent valleys strongly depends on the confinement direction and that it is orientation dependent. To explain the effect we use a simple but accurate two-band k·p model for the conduction band in silicon. Our data is in good agreement with recent results obtained by first-principle calculations.