bluuebunny/crossref_metadata_2025 huggingface dataset:
Multiscale Simulation of Electro-Chemo-Mechanical Coupling Behavior of PEN Structure under SOFC Operation
Authors: Terada Kenjiro , Kawada Tatsuya , Sato Kazuhisa , Iguchi Fumitada , Yashiro Keiji , Amezawa Koji , Kubo Momoji , Yugami Hiroo , Hashida Toshiyuki , Mizusaki Junichiro , Watanabe Hideki , Sasagawa Takashi , Aoyagi Hiroki
Published: April 2011

Numerical simulations are performed to characterize the micro- and macro-scale aspects of the electro-chemo-mechanical coupling behavior of a positive-electrolyte-negative (PEN) structure under SOFC operation. The mathematical homogenization method is applied to evaluate the macroscopic material properties of porous electrodes by performing the corresponding microscopic analyses. In particular, the potential transfer conditions at pore surfaces and triple-phase boundaries are homogenized to be source terms in the macroscopic electron-ion coupled transport problem. A case study is conducted to identify the major source of generation and evolution of cracks running through a disc-shaped cell. In this context, we are concerned especially with the effects of the radius of the cell, the thickness of an electrolyte and the profile of temperature's in-plane distribution on the macroscopic tensile circumferential stress distributions.
Numerical and Experimental Analysis of a Solid Oxide Fuel Cell Stack
Authors: Beale Steven , Le Anh D. , Roth Helmut , Pharoah Jon , Choi Hae-Won , De Haart L.G.J. , Froning Dieter
Published: April 2011

A numerical simulation of the Jülich F-design Solid Oxide Fuel Cells stack is conducted by means of an original mathematical model. The model is implemented in the open source toolbox, OpenFOAM. This cell/stack level model is a key component of a programme to develop a fully integrated multi-scale fuel cell modelling capability, from nano-scale through to system level. It is intended to share the resulting software with other parties openly. Substantial experimental data is available for the Jülich F-design; Stack configuration, flow conditions, interconnector geometries and porous electrode properties prescribed in the numerical model are based on field experiments. The numerical model generates distributions of fluid flow, species concentrations, current density and temperature. The results of the simulations are compared against experimental data obtained from short stacks.
A Micro-Scale Model for Oxygen Reduction on LSM-YSZ Cathode
Authors: Pakalapati Suryanarayana R. , Celik Ismail , Finklea Harry O. , Gong Mingyang , Liu Xingbo
Published: April 2011

In this study, a micro-scale model is developed to simulate the oxygen reduction on LSM-YSZ composite cathode. The model incorporates the effects of cathode microstructural properties on the local transport phenomena and electrochemistry inside the cathode. A detailed reaction mechanism is used in the model which has two parallel routes for oxygen conversion into oxide ions, namely two-phase boundary and three-phase boundary pathways. The model predicts field distributions of local thermodynamic values, over-potential, Faradaic current and other parameters relevant to cathode performance. Electrochemical impedance simulations are performed using the current model to analyze the contribution of various processes to the overall impedance.
Exchange Current Density of Solid Oxide Fuel Cell Electrodes
Authors: Yonekura Takahiro , Tachikawa Yuya , Yoshizumi Tomoo , Shiratori Yusuke , Ito Kohei , Sasaki Kazunari
Published: April 2011

It is desired to develop computational procedures to simulate an internal current density, anode/cathode gas concentrations and a temperature distribution in solid oxide fuel cell (SOFC) systems. In this study, the influences of various operational conditions on the exchange current density which is the essential parameter to simulate SOFC performance were discussed. The anodic exchange current density depended strongly on the humidity of H2, and it exhibited the highest value at around 40% H2O. The cathodic exchange current density was strongly affected by the operational temperature. Parameters necessary to describe dependences of exchange current density on the operational conditions were determined by fitting measured exchange current density with the empirical equations.
Numerical Simulation of Multi-Channel Planar Solid Oxide Fuel Cell Unit by Integrating Continuum Micro-Scale PEN Sub-Model
Authors: Wang Hongjian , Shi Yixiang , Cai Ningsheng
Published: April 2011

The comprehensive three-dimensional model of a 10-channel anode-supported planar solid oxide fuel cell (SOFC) unit was developed in commercial Fluent CFD modeling platform with self-designed external VC++ sub-routine for the SOFC unit by considering mass, momentum, energy and charge balance equations. The continuum micro-scale PEN sub-model coupled the processes of ionic/electronic charge transport, porous electrode diffusion as well as the effects of electrode micro-structures. The PEN sub-model was well validated by the SOFC button cell experimental data. The effects of operating conditions parameters, cell unit macro structure (inter-connector rib), as well as the porosity of anode and cathode on cell performance, and the distribution of temperature, flow rate and current density was studied in detail. The proposed model was a possible tool for combined optimization of micro-scale electrode structures and macro-scale channel geometries, which also can be expended to be applied in SOFC stack level.
Phase Field Model of Electrochemical Impedance Spectroscopy
Authors: Gathright William , Jensen Michael , Lewis Dan
Published: April 2011

A general phase field model of electrochemistry is presented in the context of simulating electrochemical impedance spectroscopy (EIS) experiments. The model tracks species, phase, and charge distribution to study the link between EIS and microstructure. Governing partial differential equations are derived from a simple set of assumptions including ideal bulk solution thermodynamics, a method of interpolating between bulk phases, physical balance laws, and the second law of thermodynamics. A source term in the conservation of mass expression captures the behavior of the chemical reactions through the interface and in the bulk phases. Two embodiments of the model are presented: finite-length diffusion in a generic electrode | mixed conducting electrolyte and semi-infinite diffusion in a system similar to an SOFC cathode. In both cases, an analytic solution was fit to the model calculations using a small number of adjustable parameters.
Effect of Porous Microstructural Properties on the Results of a Cell-Level Model in Solid Oxide Fuel Cells
Authors: Choi Hae-Won , Berson Arganthaël , Pharoah Jon , Beale Steven
Published: April 2011

A detailed micro-model framework is used for calculating effective micro-structural properties for the porous anode and cathode electrodes in solid oxide fuel cells (SOFCs). The resulting micro-structural parameters obtained from this detailed numerical approach are then applied to a macro-scale SOFC cell model. The performance of the SOFC cell model is determined by the geometric and effective transport micro-structural properties which properly accounting for representative porous SOFC electrode structures.
Mechanical, Electrical, and Optical Properties of (Pr,Ce)O2 Solid Solutions: Kinetic Studies
Authors: Bishop Sean R. , Kim Jae-Jin , Thompson Nicholas , Chen Di , Kuru Yener , Stefanik Todd , Tuller Harry L.
Published: April 2011

Praseodymium doped cerium oxide (PCO) shows mixed ionic and electronic conducting (MIEC) characteristics at relatively high pO2 (e.g. air) and enhanced oxygen storage capacity (OSC), of interest for solid oxide fuel cell (SOFC) cathodes and three way catalysts, resulting from the ready reduction of Pr to its trivalent state. This reduction also results in a change of lattice parameter, known as chemical expansion, and changes in optical absorption related to the formation of a Pr impurity band. These properties can be measured as a function of time, yielding oxide ion diffusion and surface exchange coefficients. In this manuscript, the diffusivity and/or surface exchange of PCO is explored using TGA and dilatometry of bulk specimens and HTXRD and optical absorption of thin films. The HTXRD and optical absorption measurements promise the ability to monitor both thermodynamic and kinetic properties of thin film materials exhibiting wide swings in oxygen stoichiometry.
Mechanical Properties of Ce0.9Gd0.1O2-δ at High Temperatures under Controlled Atmospheres
Authors: Kushi Takuto , Sato Kazuhisa , Unemoto Atsushi , Amezawa Koji , Kawada Tatsuya
Published: April 2011

Young's modulus of Ce0.9Gd0.1O2-δ (GDC) were investigated as functions of temperature from room temperature to 1273 K and of p(O2) from 10-24 to 10-2 bar by using a resonance method. It was found that the Young's modulus of GDC under oxidizing conditions gradually decreased with increasing temperature and was almost independent of p(O2) at a constant temperature. However, under reducing conditions, it apparently decreased as p(O2) decreased even at a constant temperature in the response to the increase in the oxygen nonstoichiometry δ. Such a p(O2) as well as a temperature dependencies of the Young's modulus can be explained by the change in the interatomic distance due to the chemical and/or the thermal expansion.
Self-Supported Thin Yttria-Stabilized Zirconia Electrolytes for Solid Oxide Fuel Cells Prepared by Laser Machining
Authors: Larrea Angel , Sola Daniel , Laguna-Bercero Miguel Angel , Peña José Ignacio , Merino Rosa Isabel , Orera Víctor
Published: April 2011

A new procedure to fabricate self-supported thin yttria-stabilised zirconia membranes by laser machining is presented. We have used a galvanometric controlled laser beam to machine the surface of a conventional sintered YSZ plate and achieved thin areas up to 10 µm thick, but also maintaining thicker support beams to ensure the structural strength of the membrane. The outer areas of the plate are left unaltered to facilitate the sealing of the cell. This kind of thin membrane is ideal to prepare electrolyte-supported Solid Oxide Fuel Cells (SOFC) operating at low temperature. The membranes have been characterized by optical profilometry, Raman Spectroscopy and Electrochemical Impedance Spectroscopy. Using the laser machined YSZ electrolyte a conventional YSZ-Ni/YSZ/LSM planar Solid Oxide Fuel Cell has been fabricated and characterized.
A Study of Coarsening Samarium Doped Ceria on Interaction with Yttria Stabilized Zirconia
Authors: Zhang Xinge , Hamel Philippe , Yick Sing , Robertson Mark
Published: April 2011

In this contribution, we studied the influence of coarsening SDC powder on interaction with YSZ powder with the purpose to alleviate the interaction between selected electrolyte materials during the cell co-firing process. The main findings are that the heat treatment of SDC increases the temperature at which a new solid solution phase combining SDC and YSZ completely forms, that the bulk conductivity of SDC+YSZ pellets is positively impacted by the coarsening of SDC through heat treatment, and that the dense pellet of the new solid solution formed by the sintering of SDC+YSZ at 1500°C in air is not stable under a reducing atmosphere. Coarsening SDC powder also led to higher sintering temperature of the SDC+YSZ powder mixture.
Single Step Preparation of Nano-Dispersed NiO/YSZ Composites for Solid Oxide Fuel Cell
Authors: Song Jung Hoon , Park Young Min , Bae Hongyoul , Ahn Jinsoo , Seong Byeong Geun , Kim Do Hyeong , Jun Joong-Hwan
Published: April 2011

In order to prepare nano-dispersed NiO/YSZ composites powders, the homogeneous co-precipitation and hydrothermal treatment were applied. Less than 100 nm sized of composites powders were successfully prepared. This process did not require the separate sintering process of YSZ and NiO to be used as the raw materials for the solid oxide fuel cell. The cell performance fabricated with the new powders showed the higher performance than the cell with the conventional powders. Co-precipitation and hydrothermal treatment was proved to be very effective process to reduce the cell production cost as well as to improve the cell performance.
X-ray Imaging and Analysis of 3D Microstructural Changes in Aged Ni-YSZ Anode
Authors: Nelson George , Izzo John , Lombardo Jeffrey , Harris William , Cocco Alex , Chiu Wilson K. , Grew Kyle N. , Faes Antonin , Hessler-Wyser Aïcha , Van Herle Jan , Chu Yong , Wang Steve
Published: April 2011

Ni-YSZ anode supports were used to fabricate test cells composed of yttria-stabilised zirconia (YSZ) electrolyte and lanthanum strontium ferrite (LSF) or lanthanum strontium manganite (LSM) / YSZ cathodes. These cells were operated at 720 °C at an average current density of 0.28 to 0.46 A/cm2. A central piece of selected anode support was extracted from tested cells and characterized using a transmission x-ray microscope (TXM). Using differential absorption imaging across the Ni K-absorption edge (8.333 keV) along with x-ray nanotomography, the 3D distribution of the Ni, YSZ, and pore phase diameters in the SOFC anode were characterized at various operational times. Significant microstructural change was observed in the Ni phase. Such an observation suggests that the microstructural reconfiguration of the phases may be correlated to SOFC performance, and may elucidate underlying fundamental mechanisms that induce such changes
A Novel Redox Stable Catalytically Active Electrode for Solid Oxide Fuel Cells
Authors: Liu Qiang , Xiao Guoliang , Howell Thomas , Reitz Thomas L. , Chen Fanglin
Published: April 2011

Ceramic electrode materials for solid oxide fuel cells (SOFCs) have attracted much attention due to their potential redox stability, carbon resistance and sulfur tolerance. Here a perovskite based on Sr2Fe1.5Mo0.5O6-δ (SFMO), which demonstrates excellent redox stability and high electrical conductivity in both reducing and oxidizing environment, has been applied as both anode and cathode for SOFCs using La0.8Sr0.2Ga0.87Mg0.13O3 (LSGM) electrolyte.
Microstructural Characterization of SOFC Electrodes: Observations and Simulations
Authors: Shearing Paul , Cai Qiong , Adjiman Claire , Marquis Andrew , Clague Ralph , Gelb Jeff , Bradley Robert , Withers Philip , Brandon N.P.
Published: April 2011

SOFC electrodes are typically porous composite materials bringing ionic, electronic and pore phases into intimate contact. These electrodes must fulfill a broad range of criteria from diffusion and electrocatalysis to mechanical support and redox tolerance. Historically design and optimisation has been largely empirical and characterisation of electrode microstructures at sub-micron length scales has been restricted to two-dimensional electron microscopy. In recent years, the development and application of focused ion beam and X-ray nano tomography tools has enabled characterisation of electrode microstructures in three dimensions providing unprecedented access to a wealth of microstructural information . As well as improving our understanding of existing electrode geometries, these tools have also been successfully applied to evaluate design and manufacturing strategies. With improved availability and functionality of high-resolution tomography tools, we can start to explore the effects of processing and operation on microstructure and performance. Using the unique benefits of non-destructive synchrotron X-ray nano-CT we have explored microstructural evolution processes in-situ using so-called "4D tomography" - facilitating an improved understanding of electrode aging and durability. These tomography platforms are however most powerful when used in conjunction with relevant simulation tools. Here we present the results of finite element simulations, exploring coupled electrochemistry and transport and stress in composite SOFC electrodes, utilising experimentally derived microstructural frameworks.
Evaluating Overpotentials in GDC Electrodes for H2/H2O Reactions in Solid Oxide Electrochemical Cells
Authors: Wang Lei , Zhang Chunjuan , Grass Michael , Yu Yi , Gaskell Karen , Hussain Zahid , Liu Zhi , Eichhorn Bryan , Jackson Gregory
Published: April 2011

Thin-film GDC (Ce0.8Gd0.2O2-x 300 nm thick) electrodes with porous Ni or Au metal overlayers (300 nm thick) were sputter-deposited on polycrystalline YSZ substrates and tested in single-chamber cells. With a back-side Pt-counter electrode, the electrochemical cells were characterized by linear-sweep voltammetry and impedance spectroscopy between 650 to 750 ºC in mixtures of H2/H2O/Ar diluent. To complement the electro-chemical tests, ambient-pressure XPS at the Advanced Light Source was performed on active cells in H2/H2O mixtures to measure surface potential and oxidation states. The GDC electrodes showed lower resistance to H2O electrolysis than H2 oxidation with Ni and Au overlayers. XPS measurements indicated large overpotentials across the YSZ/GDC interface particularly for H2 oxidation on the GDC electrode. Increasing PH2/PH2O (up to 10) resulted in higher rates for not only H2 oxidation, but also H2O electrolysis, suggesting that H2O electrolysis activity is enhanced by increased reduction of the GDC surface.
Characterization of the Ni-8YSZ Cermet Creep and Its Impact on the Cell 'Redox' Tolerance
Authors: Laurencin Jerome , Delette Gerard , Usseglio-viretta Francois , Di Iorio Stéphane , Lefebvre Florence
Published: April 2011

Creep properties of a commercial Ni-8YSZ cermet have been investigated at the SOFC operating temperatures. Experiments have shown that Ni-8YSZ cermet exhibits substantial creep strain rates. The creep activation energy and the parameters of the Norton's law have been determined from the experimental data. Impact of such behavior on cell 'redox' tolerance has been discussed for both planar SOFC configurations. Considering unused Anode Supported Cells (ASC), oxidation tests have shown that the electrolyte cracking arises as soon as ~65% of Ni is transformed into NiO. A mechanical analysis, which takes into account the cermet creep, suggests that this threshold could be lowered after a long term operation. In the case of the Electrolyte Supported Cell (ECS), the electrochemical degradation has been recorder upon several full 'redox' cycles. This degradation is found to be well correlated with the viscoplastic deformation of the cermet.
Measurement of Knudsen and Effective Ordinary Diffusion Coefficients in Solid Oxide Fuel Cell Anodes Fabricated by Atmospheric Plasma Spraying Using Powder, Suspension, and Solution Precursor Feedstocks
Authors: Metcalfe Craig , Lay Elisa , Kesler Olivera
Published: April 2011

Ni and yttria-stabilized zirconia electrode layers were fabricated by atmospheric plasma spraying using powder, suspension, and solution precursor feedstocks. Permeability measurements were used to evaluate the Knudsen diffusion coefficients for N2. It was demonstrated that the forced flow behavior for a second gas, e.g. Ar, may be determined based on the microstructural parameters obtained using N2. Graham's diffusion cell was used to obtain effective ordinary diffusion coefficients for the H2/N2 system. The values obtained for the three plasma sprayed coatings did not differ significantly. Further work is required to satisfactorily separate the diffusion coefficients for the coatings from the measured results on the support and coating combinations.
Electrooxidation of Reformate Gases at Model Anodes
Authors: Weber André , Utz Annika , Joos Jochen , Ivers-Tiffée Ellen , Störmer Heike , Gerthsen Dagmar , Yurkiv Vitaliy , Volpp Hans-Robert , Bessler Wolfgang G.
Published: April 2011

This paper summarizes the experimental and modeling results concerning the electrooxidation of hydrogen and carbon monoxide, the main oxidizable compounds in reformates, at patterned nickel anodes on polycrystalline yttria stabilized zirconia electrolytes. The line specific resistance of the three phase boundary was evaluated within a wide range of gas compositions and temperature. The investigations showed that microstructural stability, impurities, accelerated degradation and reversible dynamic changes are key issues which have to be considered. Elementary kinetic models, parameterized with literature data, temperature-programmed desorption and reaction and quantum chemical calculation results were in excellent agreement with the experimental data. For the first time it could be shown that the line specific resistance values evaluated by means of patterned anodes are applicable in homogenized and space resolved models for cermet anodes.
Adsorptive Properties of the Ni1-XCoX-Based Cermet Anode for the Oxidation of Methane
Authors: Sawahata Tatsuya , Takayanagi Hirotaka , Wah Tzu Teoh , Sato Kazunori
Published: April 2011

The adsorptive abilities of Ni1-xCox-YSZ and Ni1-xCox-CeO2 cermet particles for CH4 and CO were affected by the amount of the Co atoms substituted for the Ni atoms. The CO molecules produced by the partial oxidation of adsorbed CH4 molecules by the O2- ions at the interface between the Ni1-xCox and YSZ (or CeO2) affect the cell performance for the direct oxidation of CH4 in solid oxide fuel cells. The partial substitution of Co for Ni in the fcc lattice increased the amount of the adsorbed species, and decreased the desorption activation energy for CO and CH4.
Gas Products Analysis during the Electrochemical Conversion of Dry Methane with a La0.3Sr0.7TiO3 and Ni/YSZ Bi-Layer SOFC Anode
Authors: Buccheri Marco A. , Hill Josephine M.
Published: April 2011

The electrochemical conversion of dry CH4 was studied over a La0.3Sr0.7TiO3 (LST)-Ni/YSZ bi-layer anode at 1023 K. In order to understand the electrochemical pathway, a fuel mixture composed of H2, CH4, CO, and CO2 was fed to the SOFC anode while the gas products were analyzed at different current densities. In this fuel mixture, the Nernst potential and material balance calculated for the H2 electrochemical oxidation are consistent with the experimental OCV and the gas product analysis. In dry CH4 fuel, the electrochemical oxidation pathway is more complex. The conversion of dry CH4 strongly depends on the anode polarization. CO is formed at low current densities due to the electrochemical oxidation of carbon deposits, whereas H2O and CO2 are produced at higher currents due to the electrochemical oxidation of H2 and CO.
Impact of Ni on Accelerated Degradation of 8.5 Mol% Y2O3-Doped Zirconia
Authors: Lefarth Andreas , Butz Benjamin , Störmer Heike , Utz Annika , Gerthsen Dagmar
Published: April 2011

This study focuses on the investigation of the influence of solved nickel on the accelerated degradation of the ionic conductivity of 8YDZ (8.5 mol% Y2O3-doped zirconia) under reducing atmosphere. In comparison to pure 8YDZ, the degradation of Ni-containing 8YDZ proceeds 50 times faster and is completed after 100 h at 950 oC. The impact of Ni-incorporation into 8YDZ on microstructure and chemistry was studied by light microscopy (LM) and transmission electron microscopy (TEM). After thermal treatment under reducing atmosphere, a characteristic colour change of 8YDZ is observed by LM that is attributed to the in-diffusion (> 50 µm) of Ni into the 8YDZ substrate. TEM dark-field imaging reveals the coarsening of nano-scaled precipitates of the metastable t'-YDZ in cubic 8YDZ which is correlated with the degradation of the ionic conductivity. Since the decomposition rate of 8YDZ is determined by the mobility of Y and Zr, the dissolved Ni must have a strong impact thereon. An explanation based on the reduction of solved Ni under reducing operation conditions is proposed. It is based on the strain field which are expected to arise in the vicinity of the Ni-atoms after reduction.
Influence of Additive Oxides on Electrochemical Performance of Y-Doped SrTiO3 Anode in SOFCs
Authors: Puengjinda Pramote , Muroyama Hiroki , Matsui Toshiaki , Eguchi Koichi
Published: April 2011

A composite anode consisting of Y-doped SrTiO3 (YST) as an electron conducting phase with ceramic oxides is currently a promising candidate to overcome the shortcoming of Ni-based anode. The composite anodes with various additive oxides such as samaria-doped ceria (SDC), yttria-stabilized zirconia (YSZ), and scandia-stabilized zirconia (ScCeSZ) were prepared to evaluate the electrocatalytic performance in both hydrogen and methane fuels. The composite of YST-SDC showed the excellent performance among all composites investigated due to the superior in catalytic activity of SDC towards the oxidation of fuels. Moreover, the addition of some portions of nickel in anode composite could remarkably enhance the electrochemical performance of the anode. By 10 wt% of nickel oxide loading, the composite showed significantly increased performance in humidified hydrogen and methane without the degradation over 20 h.
Ceramic Oxide Anode with Precipitated Catalytic Nanoparticles for Ethanol Fueled SOFC
Authors: Monteiro Natalia , Nóbrega Shayenne , Fonseca Fabio C.
Published: April 2011

Carbon resistant and redox stable anodes have been intensively studied aiming at effective fuel-flex solid oxide fuel cells. Previous studies have demonstrated that the La0.75Sr0.25Cr0.50Mn0.50O3 (LSCM) perovskite has comparable performance in both hydrogen and methane fuelled SOFCs. In the present study, LSCM compounds with partial substitutions of either Mn or Cr by Ru (LSCM-Ru) were synthesized and characterized. Thermal analysis and X-ray diffraction were used to study the thermal evolution of precursor resins and phase formation. The electrical properties were investigated by 4-probe measurements in the 25 °C - 800 °C temperature range. X-ray diffraction data evidenced that single phase compounds were obtained at 1200 °C, without significant structural distortions up to ~ 10 at.% of Ru. The electrical resistivity data showed that the transport properties depend on the substituted cation. In addition, the formation of Ru nanoparticles on the surface of LSCM-Ru grains, suggest that LSCM-Ru compounds have enhanced catalytic activity for carbon containing fuels.
Evaluation of Porous Ni-YSZ Cermets with Ni content of 0-30 vol% As Insulating Substrates for Solid Oxide Fuel Cells
Authors: Wang Zhenwei , Mori Masashi , Itoh Takanori
Published: April 2011

Nickel was added to anode substrates composed of porous YSZ, in order to minimize anode damage during redox cycling in SOFCs with a YSZ electrolyte. In this study, the electrical insulating and thermal properties of these materials were evaluated for their suitability as SOFC substrates.
Mesoporous NiO-CGO Obtained by Hard Template as High Surface Area Anode for IT-SOFC
Authors: Almar Laura , Andreu Teresa , Morata Alejandro , Tarancón Albert
Published: April 2011

Mesoporous nickel-ceria cermets were synthesized and electrically characterized as anodes for intermediate-temperature solid oxide fuel cells using Ce0.8Gd0.2O1.9 as the material for the electrolyte. Mesoporous nickel-ceria cermets were prepared from silica hard templates, with KIT-6 structure, and a multistep impregnation process. A comprehensive (micro)structural analysis was carried out in order to determine the stability of the replicated mesoporous cermet at the typical processing temperatures employed in solid oxide fuel cells fabrication, i.e. from 900ºC to 1100ºC. Electrical characterization of the mesoporous cermets in symmetrical cells was carried out in humidified 5%H2 in N2 atmosphere. Targeted values of electrode/electrolyte area specific resistance were achieved in the intermediate temperature range showing the suitability of the here-presented mesoporous approach for developing a new class of high performance anodes for IT-SOFC.
Determination of Three Dimensional Microstructure Parameters from a Solid Oxide Ni/YSZ Electrode after Electrolysis Operation
Authors: Jo̸rgensen Peter S. , Bowen Jacob R.
Published: April 2011

The interface structure of a Ni/YSZ electrode tested for 1300 hours in steam electrolysis mode is analyzed. We break down the electrode interface structure measurements into total phase interfaces (e.g. total pore surface area), two-phase interfaces (e.g. Ni/YSZ interface area) and triple-phase boundaries and further analyze these based on their percolation to electron, ion and gas sources. The measurements are compared to previous related work.
Electrochemical Performance and H2S Poisoning Study of Mo-Doped Ceria (CMO) SOFC Anodes
Authors: Mirfakhraei Behzad , Birss Viola I. , Thangadurai Venkataraman , Paulson Scott , Béré Kossi E. , Gitzhofer Francois
Published: April 2011

Here we compare the electrochemical properties of a porous 10 mol. % Gd-doped CeO2 (GDC) anode with those of the same material, but infiltrated with a new plasma spray synthesized 10 mol. % Mo-doped CeO2 nano material (nCMO), all at 600-800 oC in H2, with and without added 10 ppm H2S. While both of these anode materials exhibit very good H2 oxidation activity, their performance does deteriorate when exposed to H2S. However, the nCMO-infiltrated GDC anode is significantly more stable and shows much better sulfur tolerance than the single-phase GDC anode. Furthermore, the response of both anodes is reversible, at least in early exposures, and the original H2 oxidation activity is regained fully when H2S is removed from the fuel stream. At low temperatures (ca. 500oC), these anode materials, contacted to a gold paste current collector, exhibit a dramatic response to H2S, making them of potential use as a H2S sensor.
Study on Degradation of Solid Oxide Fuel Cell with Pure Ni Anode
Authors: Jiao Zhenjun , Shikazono Naoki , Kasagie Nobuhide
Published: April 2011

In this study, the degradation phenomena at the interface between Ni and YSZ have been investigated by using screen-printed pure Ni anode sintered on YSZ pellet. The time depended microstructural evolution of Ni-YSZ interface in long time galvanostatic polarization is studied in hydrogen with different humidities. The microstructural changes were characterized by scanning electron microscopy (SEM). The inﬂuences of bulk gas humidiy, silica impurity aggregation and Ni redistribution at TPB were investigated.The degradation mechanism at Ni-YSZ interface is discussed.
Key Issues in Processing Metal-Supported Proton Conducting Anodes for SOFCs Applications
Authors: Mercadelli Elisa , Gondolini Angela , Pinasco Paola , Sanson Alessandra , Barison Simona , Fabrizio Monica
Published: April 2011

BaCe0.65Zr0.2Y0.15O3-δ (BCZY) have been recently proposed for IT-SOFCs due to its high proton conductivity. On the other hand considerable efforts are directed towards the development of metal-supported cells. The combination of the potential advantages offered by either proton conductors based cells and metal supported configuration has never been explored. In this work the technological issues to produce proton conducting BCZY-Ni anodes stainless steel-supported were carefully investigated. A tailored porous metal support was produced by tape casting. Afterwards the anode was deposited by screen printing and the resulting bilayer sintered in reducing atmosphere. Each step of the production process was thoroughly investigated. A cations interdiffusion between the metallic support and the anodic layer was observed in all range of temperatures considered. The influence of a CeO2 barrier layer and anode thickness on the cations diffusion and a successful production of planar crack-free anode was deeply analyzed.
Effect of Sm0.2Ce0.8O1.9 (SDC) for Direct Electrochemical Oxidation of Methane in Ni-Based Anode of Solid Oxide Fuel Cell
Authors: Yun Jeong Woo , Yoon Sung Pil , Park Sang Gyun , Kim Hee Su , Nam Suk Woo
Published: April 2011

Ni/SDC anode has been investigated as an alternative anode for using methane fuel and compared to the conventional Ni/YSZ anode. Moreover, to improve the cell performance, the porous SDC thin layer was coated on the pore of the anode by sol-gel coating. The mixed ionic and electronic conductive properties of SDC in reducing condition provided the additional reaction area beyond the TPB site. The governing reaction mechanism of methane in the Ni-based anode underwent through the partial electrochemical oxidation. The pyrolysis of methane causing to carbon deposition was likely occurred in the Ni/YSZ anode. However, carbon was hardly formed in the SDC coated Ni/YSZ anode due to electrochemical oxidation of methane in the entire anode and also deposited carbon could likely oxidize electrochemically.
CeO2 Addition for Improving Electrochemical Behavior of La1-xSrxMnO3 Cathodes Sintered at High Temperature
Authors: Wiff J. P. , Suzuki Masaya , Suda S.
Published: April 2011

This work evaluate the effects of CeO2 addition in La1-xSrxMnO3 (LSM) cathodes on the power density produced by cathode supported single cells co-sintered with YSZ electrolyte at high temperature (1350oC). Results show that regardless of La1-xSrxMnO3 composition, single cells containing CeO2-added LSM cathodes generate higher power density compared when no -added LSM cathodes are used. Highest power density was achieved using 6 mol% CeO2-added La0.7Sr0.3MnO3 cathode. Results suggests that both LSM composition and CeO2 addition are key factors in order to enhance the LSM and single cell performance after co-sintering with YSZ-electrolyte at 1350oC. In addition, both the maximum power density and the co-sintering temperature presented in this work correspond to the highest values as far reported without the need of a buffer layer between LSM-cathode and YSZ-electrolyte.
Sm(Sr)CoO3 Nano Cone Cathode and Ni-Fe Metal Support for High Power Density and Reliability
Authors: Ishihara Tatsumi , Ju Young-Wan , Inagaki Toru , Ida Shintaro
Published: April 2011

Dense and thin Sm0.5Sr0.5CoO3-δ (SSC) interlayer film was fabricated by a pulsed laser deposition (PLD) method on the Sm0.2Ce0.8O2-δ (SDC)/La0.9Sr0.1Ga0.8Mg0.2O3-δ (LSGM) bi-layer electrolyte film on a Ni-Fe metallic anode for intermediated temperature solid oxide fuel cells. Optimum fabrication condition of SSC interlayer has been investigated. By inserting SSC interlayer, power generation property and thermal cycling durability was improved due to an improved contact strength and expanded oxygen ion conduction path. Particularly, the cell having 500 nm thickness SSC interlayer showed higher power generation property than that of the cell without interlayer. In addition, after thermal cycling treatment from 973 to 298 K, decrease in MPD was only 4 %. The cell also showed a stable open circuit potential after re-oxidation treatment of anode at 673 K.
Doped / Undoped Ceria Buffer Layers for Improved LT SOFC Performances with Pr2NiO4+δ Cathode
Authors: Bassat Jean-Marc , Mesguich David , Ferchaud Claire , Zhang-Steenwinkel Ye , Van Berkel Frans , Aymonier Cyril , Watkins Jim , Grenier Jean-Claude
Published: April 2011

The praseodymium nickelate oxide Pr2NiO4+δ, a mixed conducting oxide, was evaluated as cathode for Low Temperature Solid Oxide Fuel Cell at T = 873 K, using zirconia-type electrolytes. The electrochemical performance of the porous cathode has been improved by optimisation of its microstructure combined with the use of a doped ceria barrier layer in between the cathode and zirconia electrolyte. Both low polarization and ohmic resistances were obtained using Pr2NiO4+δ powders with a median particle size of 0.4 µm. These manufacturing conditions resulted in a cathode microstructure with well established connections between the cathode particles and good adhesion of the cathode on the electrolyte. Full-sized anode supported cells have been manufactured using the same process conditions and tested. The best results were obtained when using a dense Ce0.8Gd0.2O1.9 (20CGO) barrier layer. Moreover, we developed a new route for depositing ceria thin films: the supercritical fluid deposition (SFD) technique. Interestingly, we could evidence that the deposit of a dense interlayer of a few tens of nanometer contributes to the lowering of the polarization resistance, but also that this result can be achieved with undoped ceria, although this material is never used for SOFC because of its low ionic conductivity level.
On the Thermodynamic Stability and the Kinetic Activity of SOFC Materials
Authors: Zhou Xiao-Dong , Templeton Jared , Stevenson Jeff
Published: April 2011

Materials research in solid oxide fuel cells has been driven by the recognition of developing novel constituents which enable faster kinetics and greater power, in order to reduce the cost of SOFC systems (e.g. $/kW). When an SOFC is operating with very high current density, the physical properties of its constituents may not be the same as these at the conditions of low current density or open circuit voltage. This is particularly true for the SOFC cathode, the reduction electrode which dissociates oxygen molecules to oxygen ions, because the cathode is generally considered to be the cell component that limits the electrochemical performance of anode-supported planar SOFCs. The aimed of this paper is to address a fundamental question: how do fast kinetics and high current in an operating SOFC affect the thermodynamic states of its material constituents.
Impact of the Volatile Cr-Species' Attack on the Conductivity of La(Ni,Fe)O3
Authors: Stodolny Maciej K. , Boukamp Bernard , Van Berkel Frans
Published: April 2011

This study demonstrates the detrimental impact of Cr on the electronic conductivity of a LaNi0.6Fe0.4O3 (LNF) porous cathode layer at 800 ºC. Vapor transport of Cr-species, originating from a porous metallic foam, and subsequent reaction with LNF results in a decrease of the electronic conductivity of the LNF-layer. Cr has been detected throughout the whole cross-section of the LNF-layer. Transmission electron microscopy revealed that Cr is gradually incorporated into the LNF-grains, while Ni is proportionally expelled. The progressing Cr deposition and penetration into the LNF-grains most likely explains the electronic conductivity drop. The Cr-poisoning impact on the electronic conductivity of the LNF porous layer is considerably smaller at 600 ºC than at 800 ºC. A tentative mechanism for the Cr attack and its influence on the electronic conductivity of the LNF layer will be presented
Microstructural Aspects on the Performance of LSCF Cathodes for SOFCs
Authors: Costa Rémi , Ilhan Zeynep , Ansar Asif
Published: April 2011

The electrode reaction of oxygen for various porous microstructures of La0.6Sr0.4Co0.8Fe0.2O3-δ cathode was investigated. The particle size distribution of the powder and the sintering parameter were changed to attain different porosity. The electrochemical performance was investigated by impedance spectroscopy in static air from 500°C up to 900°C. It was found that the increase of the total pore surface area resulted in a decrease of the average pore size leading to an increase in the concentration polarization associated with oxygen diffusion limitation. Above 600°C, this was attributed to a low frequency arc on the impedance spectra, contributing to the total cathode ASR up to 42% at 800°C. Consequently, the lower obtained ASR value (0.33Ω.cm2 at 800°C) was not correlated with microstructure having the highest pore surface area. Development of microstructure mitigating oxygen diffusion limitation and having high pore surface area is thus a major issue for high performance LSCF cathodes.
The Structural Disorder and Lattice Stability of (Ba,Sr)(Co,Fe)O3 Complex Perovskites
Authors: Kuklja Maija M. , Mastrikov Yuri , Rashkeev Sergey , Kotomin Eugene
Published: April 2011

The structural disorder and lattice stability of complex perovskite (Ba,Sr)(Co,Fe)O3, a promising cathode material for solid oxide fuel cells and oxygen permeation membranes, is explored by means of first principles DFT calculations. It is predicted that Ba and Sr ions easily exchange their lattice positions (A-cation disorder) similarly to Co and Fe ions (B-cation disorder). The cation antisite defects (exchange of A- and B-type cations) also have the low formation energy. The BSCF is predicted to exist in an equilibrium mixture of several phases and can decompose exothermically into the Ba- and Co-rich hexagonal (Ba,Sr)CoO3 and Sr- and Fe-rich cubic (Ba,Sr)FeO3 perovskites.
Strain Effects on the Surface Chemistry of La0.7Sr0.3MnO3
Authors: Han Jeong Woo , Jalili Helia , Kuru Yener , Cai Zhuhua , Yildiz Bilge
Published: April 2011

We report on the mechanistic effects of epitaxial strain on the surface chemistry, in particular the segregation of Sr cations on La0.7Sr0.3MnO3 (LSM) model dense thin films. Our results show that the LSM film surfaces are layered and exhibit strain-dependent nanoscale lateral structures. All surfaces examined here were Sr-rich. X-ray photoelectron spectroscopy shows a larger Sr segregation tendency for the tensile strained LSM films. This result is in good agreement with our first principles-based calculations, which predict lower Sr segregation energy on the tensile strained LSM surface. Our findings suggest the importance of lattice strain as a key parameter to tune the surface chemistry for facilitating oxygen reduction kinetics on transition metal perovskite cathode surfaces for solid oxide fuel cells.
Mechanistic Interpretation of the Oxygen Reduction Kinetics of La0.85Ca0.15MnO3 Cathode
Authors: Miara Lincoln , Pal Uday , Gopalan Srikanth
Published: April 2011

Experimental electrochemical impedance results from patterned half cells with La0.85Ca0.15MnO3 (LCM) cathode and 8mol% yttria doped zirconia were simulated with a state-space model (SSM) in order to estimate the value of kinetic parameters. The reaction scheme assumed dissociative adsorption followed by surface diffusion to the triple phase boundary (TPB) where full reduction and incorporation occurs. At 700°C in air the surface diffusivity was estimated at 1.3⋅10-8 cm2⋅s-1. This reaction scheme assumes Langmuir type adsorption and does not account for bulk diffusion and two phase interfacial incorporation, but for the predominately electronic conducting LCM cathode, these assumptions appear valid.
In situ Sinterable Cathode for Solid Oxide Fuel Cells
Authors: Kim Haekyoung , Park Young Min , Kim Ju Hee , Jin HyunWoo
Published: April 2011

The perovskite-based compounds having the general formula La0.6Sr0.4Co0.2Fe08O3-δ (LSCF) have been studied for improving cathode performance. The pure LSCF with high surface area of 55m2g-1 via a complexing method with metal precursors and chelating agents shows the high sinter-ability at the lower temperature. The LSCF is screen printed on Ni-YSZ support / Ni-YSZ functional layer /YSZ electrolyte / GDC buffer layer and tested without a sintering process, in-situ sintered cell. The fuel cell performance of the in-situ sintered SOFC at 790oC shows the maximum power density of 2 Wcm-2 and 1.25 Wcm-2 at 0.8 V. At 750 oC, the maximum power density is 1.5Wcm-2.
Aerosol Jet Printing and Microstructure of SOFC Electrolyte and Cathode Layers
Authors: Sukeshini A. M. , Gardner Paul , Meisenkothen Frederick , Jenkins Thomas , Miller Ryan , Rottmayer Michael , Reitz Thomas L.
Published: April 2011

We report the cathode layer optimization efforts undertaken to improve the cell performance of a previously reported (10) aerosol jet printed SOFC with strontium doped lanthanum manganate (LSM) based cathode. The cathode current collection layer, LSM with different thicknesses, solids loading in printing ink, and sintering temperature was examined. These parameters were observed to have a significant impact on the cell performance, changing the maximum power density of cells from 200 - 460 mW/cm2 at 850 ºC, depending on the processing conditions. Low voltage scanning electron microscopy was used to clearly distinguish the different phases of the composite LSM/YSZ layer. This method was used as a diagnostic tool to qualitatively assess the feasibility of "on the fly mixing" of the individually aerosolized inks. Cells with printed gadolinia doped ceria (GDC)-lanthanum strontium cobalt ferrite (LSCF) cathodes showed a performance, about twice that of cells with LSM cathodes.
Nanosized Ceria Modified GdBaCo2O5+δ Cathode for IT-SOFC
Authors: Wei Bo , Lü Zhe , Jia Dechang , He Linxiao , Huang Xiqiang , Zhang Yaohui , Su Wenhui
Published: April 2011

Nanosized ceria (CeO2) was introduced to the porous GdBaCo2O5+δ (GBCO) backbone by an infiltration technique. The XRD profile confirmed good chemical compatibility between GBCO and ceria nanoparticles. Impedance spectra confirmed that the incorporation of ceria obviously enhanced the cathode performance, with a polarization resistance a 0.19 Ohm cm2, showing promising potential for applications in IT-SOFCs.
Pr Doped Ceria and La0.6Sr0.4Co0.2Fe0.8O3 Composite Cathode for Solid Oxide Fuel Cell
Authors: Chen Mei-Ju , Cheng Soofin
Published: April 2011

The physical mixture of doped ceria and La0.6Sr0.4Co0.2Fe0.8O3 (6428LSCoF) was used as the composite cathode of intermediate temperature solid oxide fuel cell (IT-SOFC). The ceria co-doped with Pr and Mg was found to give higher current density and power density than Pr-doped 30PO and Gd-doped 20CGO. The optimal content of doped ceria in the composite cathode was determined to be around 50 wt%, which gave the polarization resistance of 3.73, 2.87 and 2.1.4 Ω.cm2 for 20CGO, 30CPO and 28,2-CPMgO, respectively, at 700°C. The highest cell performance of current density of 1110 mA/cm2 and power density of 297 mW/cm2 at 700°C was obtained by the cell with 28,2-CPMgO-6428LSCoF composite cathode.
Effect of the Strontium Content on the Electrochemical Performance of the Perovskite-Type Pr1-xSrxFe0.8Co0.2O3 Oxides
Authors: Pinedo Ricardo , Ruiz de Larramendi Idoia , Jimenez de Aberasturi Dorleta , Ruiz de Larramendi Jose Ignacio , Arriortua Maria Isabel , Rojo Teofilo
Published: April 2011

Perovskites of the system Pr1-xSrxFe0.8Co0.2O3 (PSFC) have been investigated in terms of their applicability in intermediate temperature electrochemical devices. The crystal structure, morphology, thermal expansion and electrochemical behavior of these oxides were studied by X-ray diffraction, scanning electron microscopy, dilatometry and AC impedance spectroscopy, respectively. For all compositions, orthorhombic perovskite structure was obtained with a particle size of between 1 and 10 μm. All the dilatometric curves show an increase of the thermal expansion at elevated temperatures pointing out a loss of lattice oxygen. The area specific resistances (ASR) of PSFC/YSZ/PSFC symmetrical cells were determined between room temperature and 850 ºC. The AC impedance results showed that Pr0.6Sr0.4Fe0.8Co0.2O3 exhibited the lowest cathodic polarization resistance. The ASR was 0.25 Ω cm2 at 850 ºC in air.
Cooperative Investigations on Degradation of Cathode Materials in Segment-In-Series Cells by MHI
Authors: Yokokawa Harumi , Kishimoto Haruo , Yamaji Katsuhiko , Horita Teruhisa , Watanabe Takao , Yamamoto Tohru , Eguchi Koichi , Matsui Toshiaki , Sasaki Kazunari , Shiratori Yusuke , Kawada Tatsuya , Sato Kazuhisa , Hashida Toshiyuki , Unemoto Atsushi , Kabata Tatsuo , Tomida Kazuo
Published: April 2011

Segment-in-series cell fabricated by Mitsubishi Heavy Industries have been investigated from the various experimental approaches. Examined samples are type 1 cells which were operated for up to 10,000 h by CREIPI. Analyses were made by AIST on materials transport with dynamic SIMS, by CRIEPI on microstructure observation with EPMA, by Kyoto University on microstructure change with FIB-SEM, by Kyushu University on chemical states with S-TEM, and by Tohoku University on mechanical properties in the microscopic zone with micro indentation technique. On the bases of accumulated knowledge on these samples, the materials deterioration model has been established with a focus on the movement of the Ca component in the cathode layers. The degradation rate observed in the analyses by CRIEPI can be interpreted in terms of the Cr poisoning deposited on the three phase boundaries and also of the change in microstructure.