Adsorption‐Engineered Hydrocarbon Ionomers for Durable Proton‐Exchange Membrane Fuel Cells

Abstract

ABSTRACT Reducing reliance on perfluoroalkyl substances (PFAS) in proton‐exchange membrane fuel cells requires hydrocarbon ionomers that combine high performance with long‐term durability, a persistent challenge in catalyst‐layer design. Here, we identify oxidation‐driven ionomer‐catalyst interfacial degradation as a dominant failure pathway in hydrocarbon ionomer‐bonded cathodes and introduce an adsorption‐engineering strategy to overcome this limitation. The comparison of a commercial sulfonated poly(phenylene) (Pemion) with structurally engineered sulfonated poly(fluorene)s demonstrated that electrode durability is governed by the interplay between ionomer adsorption strength and resistance to oxidative degradation on carbon‐supported Pt catalysts. A poly(fluorene) ionomer with mobile alkyl sulfonic acid groups forms resilient interfaces, delivering 1.28 A cm − 2 at 0.65 V under fully humidified H 2 /air conditions (80°C and 150 kPa abs ), comparable to Pemion. After 90,000 accelerated potential cycles, the poly(fluorene)‐bonded cathode exhibits significantly improved durability, with only 29% performance loss compared to 58% for Pemion; further molecular refinement reduces the loss to 17%, approaching that of Nafion‐bonded cathodes (14%). These findings establish adsorption‐engineered ionomer design that decouples interfacial anchoring from oxidative degradation as a general strategy for achieving durable, high‐performance PFAS‐free PEM fuel cell electrodes.