Reconstruction and Effective Transport Properties of the Catalyst Layer in PEM Fuel Cells

Abstract

In this study, a stochastic method for the microstructural reconstruction of catalyst layers in proton exchange membrane (PEM) fuel cells is presented, and empirical expressions for the effective transport coefficients in the reconstructed catalyst layers are obtained for use in macroscale fuel cell simulations. The proposed reconstruction method is based on simulated annealing, where a reconstruction problem is formulated as an optimization problem. By exploiting information from the manufacturing process and adopting a trial statistical function, the proposed method performs three-phase reconstruction, consisting of platinum/carbon, electrolyte, and gas pores, with limited experimental information on the microstructure of the catalyst layer. The lattice Boltzmann (LB) method is used to evaluate the effective diffusivity in the reconstructed catalyst layers. Because the characteristic size of pores is of the order of the mean free path of gas molecules, both molecular and Knudsen diffusion are of importance in the catalyst layer. A validated higher-order LB method is employed to consider the finite Knudsen number effects in the catalyst layer. Results show strong effects of Knudsen diffusion on reactant gas transport, especially at near-atmospheric pressures. An empirical expression for the tortuosity of the proton transport in the electrolyte phase is also obtained.