A numerical analysis of the effect of layer-scale and microscopic parameters of membrane electrode assembly in proton exchange fuel cells under two-phase conditions

Abstract

A multiphysics, multiphase, multiscale model of the membrane electrode assembly (MEA) of a polymer electrolyte membrane fuel cell (PEMFC) is presented. The model accounts for varying local effective transport that arise from assembly compression of the gas diffusion layer (GDL) and MEA microstructure, providing a more realistic description of heterogeneities. The model is validated against previous experimental data in terms of polarization curve, effect of inlet relative humidity on performance, and rib/channel saturation distribution. Then, a parametric analysis of layer-scale (compression and GDL thickness) and microscopic (pore radius and defect volume fraction) parameters is presented. The results show that performance can be improved by reducing compression under the rib (provided that electrical contact resistances are negligible), tailoring GDL thickness at intermediate values around 200μm, designing macroporous layer (MPL) and catalyst layer (CL) with pore sizes between 50–100nm and 0.5–1μm, respectively, and reducing large defect volume fractions in MPLs and CLs. To achieve these goals, an integral design of MEAs is necessary to minimize electrical contact resistances, cracks and defects, reduce inhomogeneous compression and produce highly porous multiscale structures with large continuum pore sizes at multiple scales.