The Effect of MPL Permeability on Water Fluxes in PEM Fuel Cells: A Lumped Approach

Abstract

The distribution of water fluxes in an operating polymer electrolyte fuel cell (PEFC) is strongly influenced by the properties of the cathode catalyst layer (CCL) adjacent media, viz. polymer electrolyte membrane (PEM) and microporous layer (MPL). We propose a water analysis model which treats each layer as an effective homogeneous medium. The model is applied under steady state conditions, with varying humidification of the cathode feed gas (from dry to fully saturated). We distinguish contributions to water removal due to liquid and vapor transport via anode and cathode. The model warrants definition of a critical current density up to which water removal out of the CCL to the cathode side proceeds completely via vapor diffusion. Above the critical current density, excessive water generation leads to the build-up of an excess liquid pressure in the CCL, which acts as a driving force for hydraulic fluxes to PEM and MPL sides.