Liquid Water Transport in Polymer Electrolyte Fuel Cells With Multi-Layer Diffusion Media

A two-phase, multi-component, full cell model is developed in order to analyze the two-phase transport in polymer electrolyte fuel cells with multi-layer cathode gas diffusion media, consisting of a coarse gas diffusion layer (GDL) (average pore size ~ 10 μm) and a micro-porous layer (MPL) (average pore size ~ 0.2–2 μm). The relevant structural properties of MPL, including average pore size, wettability, thickness and porosity are examined and their effects on liquid water transport are discussed. It is found that MPL promotes back-flow of liquid water across the membrane towards the anode, consequently alleviating cathode flooding. Furthermore, it is seen that unique porous and wetting characteristics of MPL causes a discontinuity in the liquid saturation at MPL-GDL interface, which in turn reduces the amount of liquid water in cathode catalyst layer-gas diffusion medium interface in some cases. Our analyses show that the back-flow of liquid water increases with the increasing thickness and decreasing pore size, hydrophobicity and bulk porosity of the MPL.