Pore-scale study of liquid water transport in gas diffusion layers with in-plane non-uniform distributed pore size of polymer electrolyte membrane fuel cell

Abstract

Timely removal of liquid water and the supply of the reaction gas in the gas diffusion layer (GDL) plays a critical role in improving the performance of polymer electrolyte membrane fuel cells (PEMFCs). Modifying the design of the GDL structure is an effective strategy for regulating the percolation process of liquid water and the supply of reaction gas. In this study, several GDLs with in-plane nonuniformly distributed pore sizes were designed to construct an ordered liquid water transport pathway. Two pore-size patterns with a “V” shape and an inverted “V” shape were designed through the orientation control of fiber distribution. In the inverted V-shaped pattern, the pore size exhibited a wave crest distribution along the in-plane direction, whereas, in the V-shaped pattern structure, the pore size was troughed along the in-plane direction. The three-dimensional (3D) multiphase Lattice Boltzmann method (LBM) and 3D diffusion LBM were used to investigate the liquid water percolation process and the reaction gas transport process in the GDL, respectively. The numerical results indicated that liquid water tends to concentrate in layers with macropores in the nonuniform GDL. Compared with the uniformly distributed GDL, these two pore size patterns can accelerate the drainage velocity and lower the water content. The reversed V-shaped pattern was further optimized to obtain the optimal width of the layers with macrospores. The results showed that a length of 96 μm is recommended to balance the concentrated effect and low-concentration areas. Under dry conditions, the gas transport capacity was insensitive to pore size distribution, whereas, under partially saturated conditions, both the V-shaped and inverted V-shaped structures of a nonuniform design weakened the impeding effect of liquid water on the gas supply. Moreover, the effective gas diffusion coefficient of the nonuniform study can reach up to 3.85 times of the uniform structure. This work promotes the understanding of different in-plane distributed pore size styles on the water percolation behavior in the GDL, thereby contributing to the optimal design of the GDL and PEMFCs.