Two-phase flow in the mixed-wettability gas diffusion layer of proton exchange membrane fuel cells

Polytetrafluoroethylene (PTFE) is widely employed to improve the hydrophobicity of gas diffusion layer (GDL) in proton exchange membrane (PEM) fuel cells. In this study, the effects of different PTFE loadings on the relationship of the capillary pressure Pc and water saturation s in the mixed-wettability GDL, i.e. Pc-s, are investigated using a three-dimensional (3D) volume of fluid (VOF) model. The simulated Pc-s curves are presented and compared with results obtained from the lattice Boltzmann model (LBM) and experiments. The good agreement between the VOF predictions and experiment data is achieved, indicating that the mixed wettability in the PTFE treated GDL is an important feature to understand two-phase behaviors in fuel cells. The homogeneous and heterogeneous PTFE distributions resulted from two PTFE drying methods (i.e. the vacuum and air dryings, respectively) are studied. It was found that the air drying GDL yields a high PTFE concentration near the water inlet and reduces water imbibition near the inlet. The simulated Pc-s correlation from VOF model was compared with standard Leverett correlation.