The effect of MPL permeability on water fluxes in PEM fuel cells: Experimental verification

The distribution of water fluxes is strongly influenced by the properties of the media adjacent to the cathode catalyst layer (CCL), viz. polymer electrolyte membrane (PEM) and gas diffusion media (GDM). We propose a model that is applied under varying humidification of the cathode feed gas, with water removal in liquid and vapor form. The model warrants the definition of a critical current density up to which water removal out of the CCL could proceed completely via vapor diffusion to the cathode side. Above the critical current density, excessive water generation leads to the build-up of an excess liquid pressure in the CCL, which drives hydraulic fluxes to PEM and GDM sides. Experimental data from literature were analyzed and found to be in good agreement with predictions of the model. This analysis reveals that the effective liquid water permeability of commercial GDMs (that includes an MPL) lies within the same order of magnitude of the liquid water permeability of the PEM.