Multimodal mass transfer in solid-oxide fuel-cells

This article presents a numerical framework for the computation of the effective transport properties of solid oxide fuel cells (SOFCs) porous electrodes from three-dimensional (3D) constructions of the microstructure. Realistic models of the 3D microstructure of porous electrodes are first constructed from measured parameters such as porosity and particle size distribution. Then each phase in the model geometries is tessellated with a computational grid. Three different types of grids are considered: Cartesian, octree, and body-fitted/cut-cell with successive levels of surface refinement. Finally, a finite volume method is used to compute the effective transport properties in the three phases (pore, electron, and ion) of the electrode. To validate the numerical approach, results obtained with the finite volume method are compared to those calculated with a random walk simulation for the case of a body-centred cubic lattice of spheres. Then, the influence of the sample size is investigated for random geometries with monosized particle distributions. Finally, effective transport properties are calculated for model geometries with polydisperse particle size distributions similar to those observed in actual SOFC electrodes.

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“…It is written in the object-oriented C++ programming language. Recently, OpenFOAM has been applied to some fuel cell applications [72][73][74].…”

Section: Finite Volume Methodsmentioning

confidence: 99%

Effective transport properties of the porous electrodes in solid oxide fuel cells

Choi

Berson

Pharoah

et al. 2011

Proceedings of the Institution of Mechanical Engineers, Part A:

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“…However, due to its complexity, this model has no analytical solutions, and the corresponding analysis requires complicated numerical simulation. 2,3,6,[23][24][25] In this work, we derive analytical formulae for the diffusion impedance of all three models that allow us to accurately test their validity against experimental data.…”

Section: Theorymentioning

confidence: 99%

“…It is thought that the Dusty Gas Model should be the most accurate, although it is also the most complicated and difficult to validate. Almost no analytical results are available, but the Dusty Gas Model has been used in a number of numerical simulations, [2][3][4]8,9 albeit with constant pressure approximation which is inconsistent 9 (see below). Moreover, no theoretical framework exists to analytically derive the diffusion resistance values from impedance data using these more complex diffusion models for porous media.…”

mentioning

confidence: 99%

“…Therefore, gas transport through the porous electrode is an essential factor determining the overall cell performance. 2,3 The efficacy of the gas transport through the porous electrodes often determines the rate of electrochemical reaction or current generation. Furthermore, many researches have shown that the gas transport through porous electrodes is mainly governed by gas diffusion with very small convection contribution.…”

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confidence: 99%

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Multicomponent Gas Diffusion in Porous Electrodes

Jiang

Poizeau

et al. 2015

J. Electrochem. Soc.

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Multicomponent gas transport is investigated with unprecedented precision by AC impedance analysis of porous YSZ anodesupported solid oxide fuel cells. A fuel gas mixture of H 2 -H 2 O-N 2 is fed to the anode, and impedance data are measured across the range of hydrogen partial pressure (10-100%) for open circuit conditions at three temperatures (800 • C, 850 • C and 900 • C) and for 300 mA applied current at 800 • C. For the first time, analytical formulae for the diffusion resistance (R b ) of three standard models of multicomponent gas transport (Fick, Stefan-Maxwell, and Dusty Gas) are derived and tested against the impedance data. The tortuosity is the only fitting parameter since all the diffusion coefficients are known. Only the Dusty Gas Model leads to a remarkable data collapse for over twenty experimental conditions, using a constant tortuosity consistent with permeability measurements and the Bruggeman relation. These results establish the accuracy of the Dusty Gas Model for multicomponent gas diffusion in porous media and confirm the efficacy of electrochemical impedance analysis to precisely determine transport mechanisms. The Solid Oxide Fuel Cell (SOFC) is currently the highesttemperature fuel cell in development and can be operated over a wide temperature range from 600• C-1000• C allowing a number of fuels to be used. To operate at such high temperatures, the electrolyte is a thin, nonporous solid ceramic membrane that is conductive to charge carrier, O 2− ions. The operating efficiency in generating electricity is among the highest of the fuel cells at about 60%.1 Furthermore, the high operating temperature allows cogeneration of high-pressure steam that can be used in many applications. Combining a hightemperature SOFC with a turbine into a hybrid fuel cell further increases the overall efficiency of generating electricity with a potential of an efficiency of more than 70%.1 Therefore, it is a very promising alternative energy source that could potentially be used for home heating or large scale electricity production in the future.Solid oxide fuel cell consists of a porous cathode, an electrolyte, a porous anode and interconnects. Two different types have been explored in the development of SOFC, the electrolyte supported cell and the electrode supported cell. In the former, electrolyte is the thickest and serves as the mechanical support for the whole cell. However, due to the high Ohmic resistance of the relatively thick electrolyte layer, the electrolyte supported design has been gradually replaced by the new electrode supported cells, in which one of the porous electrodes is the supporting structure. Moreover, since cathode supported cell usually gives higher resistance, and is much harder to fabricate due to the mismatched thermal expansion coefficient of cathode support and functional layer, the anode supported cell (ASC) is the most widely accepted design in current SOFC research.The solid oxide fuel cell is operated with fuel and oxidant being continuously fed from two sides of the ce...

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“…(2) Reaction sites (TPBs) are assumed to be uniformed distributed and well percolated inside electrodes. (3) Since the convection flow and pressure gradient effect could be safely neglected [10][11][12], only diffusion is considered for gas transport inside the porous electrodes.…”

Section: Model Developmentmentioning

confidence: 99%

Investigation of the electrochemical active thickness of solid oxide fuel cell anode

Zheng

2014

International Journal of Hydrogen Energy

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Multimodal mass transfer in solid-oxide fuel-cells

Cited by 27 publications

References 28 publications

Effective transport properties of the porous electrodes in solid oxide fuel cells

Effective transport properties of the porous electrodes in solid oxide fuel cells

Multicomponent Gas Diffusion in Porous Electrodes

Investigation of the electrochemical active thickness of solid oxide fuel cell anode

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