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Reduced models for the cathode catalyst layer in PEM fuel cells

Abstract: We study a pore scale model for the catalyst layer on the cathode side of a fuel cell, where hydrogen and oxygen combine at catalyst sites. Our model distinguishes microscopically the phases of rigid structure, electrolyte, pore-space, and catalyst. The oxygen concentration and the protonic potential are described by diffusion equations with reaction terms on the catalyst’s surface. For the limit of a vanishing pore size we derive homogenized equations of reaction-diffusion type and provide formulae for the effective coefficients. A dimensional reduction shows that a thin catalyst layer can be replaced by a boundary condition. We furthermore analyze the effect of a doubling of the Tafel slope for high protonic potentials and determine effective constants.