Two-phase transport in polymer electrolyte fuel cells with bilayer cathode gas diffusion media

A two-phase, full cell model based on the multiphase mixture (M ²) framework is developed to analyze the two-phase transport in polymer electrolyte fuel cells with bilayer cathode gas diffusion media (GDM), consisting of a coarse gas diffusion layer (GDL) with an average pore size around 10-30 μm and a microporous layer (MPL) with an average pore size ranging from 0.1 to 1 μm. Effects of the relevant properties of the MPL on liquid water transport are examined, including average pore size, wettability, thickness, and porosity. It is quantitatively shown that the MPL increases the rate of water back-flow across the membrane toward the anode by increasing the hydraulic pressure differential across the membrane, consequently reducing the net amount of water to be removed from the cathode. Furthermore, it is seen that different microporous and wetting characteristics of the MPL cause a discontinuity in the liquid saturation profile at the MPL-GDL interface, which in turn reduces the amount of liquid water in the catalyst layer-MPL interface. Our analyses show that the back-flow of liquid water increases with increasing hydrophobicity and thickness, and decreasing pore size aniporosity of the MPL.