Mass Transfer in Microporous Layers for Polymer Electrolyte Fuel Cells Analyzed with Pore Network Modeling

The application of a microporous layer (MPL) to the catalyst layer (CL) side of the gas diffusion layer substrate of a polymer electrolyte fuel cell (PEFC, PEMFC) is effective to mitigate liquid water accumulation at the CL that inhibits oxygen transport to the cathode CL (Flooding). To elucidate the effects of two-phase flow on the oxygen transport in an MPL for its optimized designs, we have modeled three-dimensional porous structures of in-house hydrophobic MPLs with pore network models (PNMs) for convective air permeation and oxygen diffusion with liquid water saturation. Pore diameter distributions derived by a focused ion beam scanning electron microscope (FIB-SEM) are used to construct the PNMs. Oxygen diffusion measurements by using gas chromatography with changing wetting liquid saturation, as well as air permeation measurements, validate the PNMs.