Pore-scale study of coupled charge, gas, and liquid water transport in the catalyst layer of PEM fuel cells

Understanding the catalyst layer (CL) structure-process-performance relationship is essential for optimizing proton-exchange membrane fuel cells. This study stochastically reconstructs a high-resolution porous CL with a full thickness of 8 mu m. The liquid water distribution within CL is simulated by a capillary condensation model, and a pore-scale model coupling oxygen and proton transport with electrochemical reaction is developed to investigate the CL structure-performance relationship under different operating conditions. Results indicate that CL exhibits better performance at higher humidities, up to the flooding threshold at the water saturation of 0.41, as the benefits of increased electrochemical surface area, enhanced proton conductivity, and improved oxygen permeability through the ionomer film significantly outweigh the increased transport resistances through both the pores and the water film. Under the flooding condition at water saturation of 0.41, CL performance starts to decline due to the sharply increased pore resistance. Proper perforation of CL is suggested to alleviate the pore resistance in flooded electrodes. Additionally, reducing the Pt-to-C mass ratio is found to achieve better Pt dispersion in low Pt-loaded electrodes, thereby lowering the local oxygen resistance, and the bilayer CL design with higher Pt content on the membrane side is shown to further mitigate the performance degradation.