Effective Transport Coefficients for Porous Microstructures in Solid Oxide Fuel Cells

Abstract

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

Estimation of Chemical and Transport Processes in Porous, Stoichiometric LSM Cathodes Using Steady-State Polarization and Impedance Modeling

“…17, is the porosity and is the tortuosity. The electrode tortuosity has been estimated 37,38 to be 2. The Knudsen diffusivity, which depends on the average pore diameter, D K eff , is…”

Connected Three-Phase Boundary Length Evaluation in Modeled Sintered Composite Solid Oxide Fuel Cell Electrodes

“…One method of gaining insight into these relationships is the development of detailed three-dimensional ͑3D͒ electrode geometry models, either numerically [1][2][3][4][5][6] or by constructing representations of real electrodes using methods such as focused ion beam-scanning electron microscopy ͑FIB-SEM͒ [7][8][9][10] or X-ray computed tomography ͑XCT͒. 11,12 Key microstructural parameters such as the connected three-phase boundary length ͑TPBL͒ density 1,4 and effective transport properties such as electronic and ionic conductivities and gas diffusivity 13 can be extracted from the resulting geometrical models. These volume averaged properties can then be used in continuum electrode models for electrochemical performance evaluation.…”

Effective Transport Properties

“…Regarding SOFCs, Choi et al (2009) analyzed the effective electrical and ionic conductivity and gas diffusivity (including Knudsen diffusion) of the anode and cathode electrodes. The microstructures were made of randomly distributed and overlapping spheres with particle size distributions that matched those of ceramic powders.…”

“…The microstructure of the porous media can be obtained from (1) tomography images (García-Salaberri et al 2015a, b, 2018 or can be (2) virtually generated using numerical algorithms (Choi et al 2009;Choi et al 2011;Bertei et al 2014). Volumeaveraged quantities (e.g., composition fraction) and statistical descriptors (e.g., pore size distribution, n-point correlation functions, lineal path function, and chord length function) can be used as objective variables (Pant et al 2014).…”