Examining Invasion‐Percolation Across the Cathode Layered Assembly in Polymer Electrolyte Membrane Fuel Cells: Oxygen Resistance, Wettability and Cracks

Abstract

Efficient evacuation of water generated by oxygen reduction reaction is necessary to increase catalyst utilization in polymer electrolyte membrane Fuel Cells. However, analysis of two‐phase transport is challenged by the wide range of pore sizes present in the membrane electrode assembly (MEA), varying from 10–100 nm in the catalyst layer (CL), 10–1000 nm in the microporous layer (MPL) and 10 μm in the gas diffusion layer (GDL). In this work, a novel multiscale invasion‐percolation model accounting for the cathode CL, MPL and GDL is presented. Saturation in the macroporous GDL is modeled through an all‐or‐nothing invasion law (empty/filled), while a macroscopic description in terms of the capillary pressure curve is adopted for the MPL and the CL. The oxygen transport resistance across the cathode MEA is quantified using the computed saturation distributions. Among other conclusions, the results show that MPL addition is crucial to avoid local flooding at the CL/GDL interface, providing localized access points to the GDL rather than massively invading interfacial macropores. However, excessive MPL hydrophobicity can cause CL flooding. Water removal from the CL can be enhanced by using a more hydrophilic MPL, a hydrophobic CL or the addition of a moderate volume fraction of cracks. Oxygen transport can be further improved by modulating the arrangement of water in the GDL with patterned wettability, provided that the number of MPL cracks is low.