Variational-principle-optimized porosity distribution in gas diffusion layer of high-temperature PEM fuel cells

Abstract

Porosity distribution in gas diffusion layer has a significant impact on cell performance by affecting the oxygen transport and the electrical conductivity. This contribution presents a theoretical optimization model for porosity distribution in the cathode gas diffusion layer based on the variational principle. First, the optimization equations for maximizing the total oxygen mass flux diffused through the cathode gas diffusion layer are derived with the constraints of the momentum conservation, the species conservation and the specified average porosity. Then, the application of a typical high-temperature proton exchange membrane fuel cell with twelve parallel flow channels gives the optimized three-dimensional non-uniform porosity distribution that could increase the current density at 0.2 V by 13.7% and the maximum power density by 10.0%. Besides, the optimized porosity distribution also improves the uniformity of oxygen mass fraction field and the current density distribution. Finally, seven design schemes with in-plane non-uniform porosity distribution or thickness-direction linear gradient porosity are proposed and evaluated. The results indicate that the optimized porosity distribution has the best performance, followed by the in-plane non-uniform porosity, and the linear gradient porosity along the thickness direction shows the weakest improvement. This finding further demonstrates the rationality and necessity of the proposed optimization model.