Pore-scale simulation of two-phase flow and oxygen reactive transport in gas diffusion layer of proton exchange membrane fuel cells: Effects of nonuniform wettability and porosity

Enhancing oxygen transport and reducing water flooding in the gas diffusion layer (GDL) of proton exchange membrane fuel cells are important for improving cell performance. In this study, a pore-scale model based on the lattice Boltzmann method is proposed, which considers two-phase flow, oxygen diffusion and electrochemical reaction in the GDL. The invasion speed of the water into the GDL is determined by the water generation rate and correspondingly the oxygen consumption rate. The model is then adopted to study effects of wettability and porosity distribution on the liquid water saturation, oxygen concentration and current density. The results demonstrate that while reducing the total saturation in the GDL is important, decreasing the local saturation near the microporous layer (MPL)/GDL interface is also crucial for enhancing cell performance. It is found that GDL with locally enhanced hydrophobicity at the MPL/GDL interface or gradually increased porosity from the GDL bottom to the GDL top can improve cell performance. Particularly, by delicately designing the GDL porosity, the current density can be considerably increased by 201%. The developed pore-scale model provides a useful tool for understanding the underlying multiphase reactive transport processes in GDL and designing the microscopic structures of GDL.