Pore-Scale Simulation of Effective Transport Coefficients in the Catalyst Layer of Proton Exchange Membrane Fuel Cells

The catalyst layer (CL) of the proton exchange membrane (PEM) fuel cells is reconstructed using the sphere-based simulated annealing (SA) method. By changing carbon phase volume fraction and ionomer loading, the transports of oxygen, water vapor and proton inside the reconstructed CLs are studied using the D3Q7 multiple-relaxation-time (MRT) lattice Boltzmann (LB) method. The results show that Knudsen diffusion has an important role in gas diffusion in CL. The carbon phase distribution influences the gas diffusion process but has little effect on proton conduction. The simulated effective gas diffusivities in CL can fit the experimental data very well if using directly measured porosities, and a fitting formula is proposed to predict the effective diffusivity with porosity. Besides, the simulated effective proton conductivities in CL are in reasonable agreement with the experimental data if considering the ionomer swelling and proton conduction in the condensed water. The influence of the structural randomness of CL during the reconstruction process on the pore-scale simulations is also analyzed. The results show that the relative errors caused by structure randomness for the same structural parameters are not obvious. Therefore, a small number of reconstruction samples are enough to simulate the reasonable transport parameters of CL.