3D finite element model for reconstructed mixed-conducting cathodes: I. Performance quantification

Carraro, Thomas; Joos, Jochen; Rüger, Bernd; Weber, André; Ivers-Tiffée, Ellen

doi:10.1016/j.electacta.2012.04.109

Cited by 81 publications

(69 citation statements)

References 24 publications

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“…11 Moreover, calculations of cathode performance, spatial distribution of concentration profiles and current distributions came into reach. 18,19 However, even this ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address.…”

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confidence: 93%

Time-Dependent 3D Impedance Model of Mixed-Conducting Solid Oxide Fuel Cell Cathodes

Häffelin

Joos

Ender

et al. 2013

J. Electrochem. Soc.

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A time-dependent three-dimensional (3D) impedance model of mixed ionic electronic conducting solid oxide fuel cell (SOFC) cathodes that considers the complex coupling of gas diffusion, surface exchange, ionic bulk-diffusion and electrolyte conductivity is presented. By using the finite element method, this model enables the time-dependent and space-resolved simulation of the physicochemical processes in a porous cathode microstructure. The developed model is used for a detailed analysis of the formation of a 'Gerischer-type' impedance. It is detected that the low-frequency part is dominated by the surface exchange reaction, whereas the typical 45 • ramp of the Gerischer impedance is related to the ionic diffusion in the bulk. The capability of the time-dependent 3D impedance model is evaluated versus a well-established homogenized analytical model. For homogeneous 3D microstructures both models calculate impedance curves which are in excellent agreement. Further impedance simulations with microstructures containing features of high-performance SOFC cathodes clearly show that model separates and quantifies the contribution of the gas diffusion in a porous cathode layer. At an oxygen partial pressure of 0.21 atm the gas diffusion accounts for only 2% of the total polarization resistance, whereas a depletion of oxygen to 0.01 atm significantly increases this value to 38%.Intermediate temperature solid oxide fuel cells (SOFCs) own high potential and flexibility for an efficient conversion of fuels (from pure hydrogen to higher hydrocarbons) to electric power. The performance of SOFC single cells with a thin-film electrolyte of 1 μm is dominated by the polarization losses of both electrodes. Thus, mixed ionic-electronic conducting (MIEC) cathode materials such as La 1-x Sr x Co 1-y Fe y O 3-δ (LSCF) are indispensable at operating temperatures below 750 • C. 1,2 Due to the high oxygen ion conductivity of LSCF, the cathode performance is determined by the oxygen ion transport in the porous solid phase and the exchange kinetics of oxygen between the gas phase and the LSCF surface. Extending this electrochemically active region results in a lower value of the area specific resistance of the cathode (ASRcat), which is the mostly reported performance index. However, the coupling of transport process and surface reaction process in a single phase demands for a properly adapted chemical composition and microstructure.Electrochemical impedance spectroscopy (EIS) has become a state-of-the-art method for the characterization of SOFC electrodes. Recent developments have introduced the combined approach of EIS measurements and the distribution of relaxation times (DRT) method, 3 leading to a physically motivated equivalent circuit model for a complete SOFC single cell. 4 The DRT method offers a higher resolution of the individual loss mechanisms due to their specific kinetics, and enables a more detailed investigation on operating conditions. The MIEC cathode is modeled by a Gerischer-type impedance, 5 and detailed investigation...

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confidence: 93%

Time-Dependent 3D Impedance Model of Mixed-Conducting Solid Oxide Fuel Cell Cathodes

Häffelin

Joos

Ender

et al. 2013

J. Electrochem. Soc.

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“…A CFD analysis was then performed for 3D microstructure. Similarly, Carraro et al [18] used 3D cathode microstructure in the advanced CFD analysis. The distribution of the oxygen concentration in the cathode was analyzed.…”

Section: Introductionmentioning

confidence: 99%

Three dimensional stress analysis of solid oxide fuel cell anode micro structure

Çelik

İbrahimoğlu

Toros

et al. 2014

International Journal of Hydrogen Energy

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“…These changes are also manifest in the quantitative features of the microstructure, many of which we are only beginning to quantify experimentally or model computationally . Using three‐dimensional (3D) reconstructions of model systems, the total length of active TPBs were isolated as the key parameter that controls cathode activity . Complete 3D descriptions of the crystallographic nature of microstructural features have been also obtained on small regions of SOFCs, as well as on dense yttria‐stabilized zirconia (YSZ) .…”

Section: Introductionmentioning

confidence: 99%

“…1 The correlation between long-term SOFC performance and cathode microstructure evolution has already been demonstrated, primarily implicating grain coarsening, redistribution of phases, and formation of resistive secondary phases at the triple phase boundaries (TPBs). [2][3][4][5][6][7][8][9][10][11][12][13][14] These changes are also manifest in the quantitative features of the microstructure, 4,5,8,[11][12][13][14][15] many of which we are only beginning to quantify experimentally 14,[16][17][18][19][20][21][22][23] or model computationally. 24 Using three-dimensional (3D) reconstructions of model systems, the total length of active TPBs were isolated as the key parameter that controls cathode activity.…”

Section: Introductionmentioning

confidence: 99%

Crystallography of Interfaces and Grain Size Distributions in Sr‐Doped LaMnO₃

et al. 2014

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Grain‐boundary plane distributions (GBPDs), grain size distribution (GSDs), and upper tail departure from log‐normal GSDs were quantified in dense and porous La0.8Sr0.2MnO3 samples to understand expected microstructures in solid oxide fuel cells. Samples were sintered at 1450°C for 4 h and then annealed between 800°C and 1450°C. The GBPDs and normalized GSDs reached steady state during sintering and little variation occurred during annealing. The GBPDs were nearly isotropic, with the relative areas of {001} planes being slightly higher than random (and the relative areas of {111} planes being less than random). The porous sample had an almost identical GBPD, whereas the almost isotropic pore boundary plane distribution was essentially opposite to the GBPD. The upper tails of the experimental GSDs, and several theoretical distributions, were characterized using peaks‐over‐threshold analysis. Dense samples, and all normal grain growth models, exhibit lower frequencies of large grains in the upper tail than would a log‐normal distribution, and the experimental distributions are similar to the Mullins distribution. Porous samples, however, have an anomalous increased frequency of large grains in the upper tail, as compared to all the model distributions, even though other metrics of the microstructure indicate the dense and porous systems are similar.

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3D finite element model for reconstructed mixed-conducting cathodes: I. Performance quantification

Cited by 81 publications

References 24 publications

Time-Dependent 3D Impedance Model of Mixed-Conducting Solid Oxide Fuel Cell Cathodes

Time-Dependent 3D Impedance Model of Mixed-Conducting Solid Oxide Fuel Cell Cathodes

Three dimensional stress analysis of solid oxide fuel cell anode micro structure

Crystallography of Interfaces and Grain Size Distributions in Sr‐Doped LaMnO₃

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3D finite element model for reconstructed mixed-conducting cathodes: I. Performance quantification

Cited by 81 publications

References 24 publications

Time-Dependent 3D Impedance Model of Mixed-Conducting Solid Oxide Fuel Cell Cathodes

Time-Dependent 3D Impedance Model of Mixed-Conducting Solid Oxide Fuel Cell Cathodes

Three dimensional stress analysis of solid oxide fuel cell anode micro structure

Crystallography of Interfaces and Grain Size Distributions in Sr‐Doped LaMnO3

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Crystallography of Interfaces and Grain Size Distributions in Sr‐Doped LaMnO₃