Performance enhancement of polymer electrolyte membrane fuel cells with a hybrid wettability gas diffusion layer

A numerical simulation by using a three-dimensional multiphase polymer electrolyte membrane (PEM) fuel cell model and the volume of fluid (VOF) method is performed to investigate a newly designed hybrid wettability gas diffusion layer (GDL) for performance enhancement of PEM fuel cells. The hybrid wettability GDL has interchangeable distributions of relatively low and high hydrophobic regions along the gas flow direction. The low hydrophobic regions are characterized by high porosity and low water removal performance, whereas the high hydrophobic regions have low porosity and strong water removal ability. Simulation results show that the water removal process, mass diffusion and output performance of fuel cells greatly depend on the wettability degree distribution in the hybrid wettability GDL. In comparison with conventional GDL designs, the hybrid wettability GDL with polytetrafluoroethylene (PTFE) content of 10 wt% and 20 wt% for low and high hydrophobic regions at 1.5 mm intervals exhibits advantages in the enhancement of water removal from the gas flow channel and the mass diffusion within porous electrodes. Therefore, it can improve the uniform distribution of oxygen, the liquid water saturation and the reaction rate and ultimately benefit the stable operation and output performance of PEM fuel cells. Result also shows that the limiting current density of the optimal hybrid wettability GDL increases by 4.45% compared with that of the conventional GDL with PTFE content of 20 wt%. Furthermore, the study reveals that hybrid wettability GDL designs exhibit a greater advantage at high RHs than at low RHs.