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

• Published in: ChemElectroChem Vol. 11; no. 13
• Main Author: García‐Salaberri, Pablo A.
• Format: Journal Article
• Language: English
• Published: Weinheim John Wiley & Sons, Inc 02.07.2024; Wiley-VCH
• Subjects: Assembly; Capillary pressure; capillary transport; Catalysts; Cathodes; Chemical reduction; Cracks; Diffusion layers; Electrolytes; Electrolytic cells; Fuel cells; Gaseous diffusion; Hydrophobicity; MEA; multiscale; Oxygen; Oxygen reduction reactions; oxygen resistance; PEMFC; Percolation; Polymers; Pressure curve; Proton exchange membrane fuel cells; Wettability
• DOI: 10.1002/celc.202400068
• ISSN: 2196-0216

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. Water and oxygen transport across the cathode layered assembly play a crucial role in the performance of polymer electrolyte membrane Fuel Cells. The present work examines the effect of microporous layer (MPL), wettability, crack density and patterned wettability on capillary transport of water and oxygen diffusion. Among other conclusions, the results show that mass transport losses can be reduced both through the incorporation of an MPL with a moderate number of cracks and the introduction of patterned wettability into the gas diffusion layer.