Mitigating Cation Contamination in PEMFC Ionomers: Mechanisms and Strategies

Abstract Proton exchange membrane fuel cells (PEMFCs) have gained growing attention due to their high energy efficiency and environmental benefits. However, their long-term performance is challenged by cation contaminants such as Co2+ and Fe2+. These species transport into the membrane electrode assembly and competitively occupy sulfonic acid sites in the ionomer, leading to chemical and structural degradation of both the membrane and catalyst layer (CL). Such interference affects ion conductivity, water management, oxygen transport, and consequently the overall fuel cell performance. This review presents a comprehensive overview of cation contaminant sources—including catalyst dissolution, trace impurities, radical scavengers, and leaching from system components—as well as their effects and transport mechanisms within the ionomer phase. Furthermore, this work discusses state-of-the-art mitigation strategies, including material design approaches aimed at restricting cation access, immobilizing cation contaminants, and reducing cation transport rate through the membrane and CL. This review provides a mechanistic foundation for future strategies to enhance the long-term performance of PEMFCs.