Study of free radical degradation mechanisms of membrane electrode assembly based on ultraviolet/hydrogen peroxide advanced oxidation process

Abstract

The main challenges in the commercialization of proton exchange membrane fuel cells (PEMFCs) are their high cost and poor durability; one of the key factors limiting their lifetime is the attack of free radicals (•OH) on membrane electrode assemblies. In this study, a quantitative free-radical aging device is built based on an ultraviolet (UV)/hydrogen peroxide (H₂O₂) Advanced Oxidation Process, which precisely regulates the generation rate of hydroxyl radicals. The results show that free-radical attack leads to polymer backbone and side-chain breakage, as well as the loss of sulfonic acid groups. The tensile strength and water absorption properties of the catalyst-coated membrane (CCM) are significantly reduced, while the gas permeability remains stable. The catalyst layer (CL) thickness decreases, and the mass loss rate increased. The hydrophobicity of the microporous layer (MPL) surface decreases continuously with the free-radical attack, the first 10 h, rapid defluorination and initial oxidation lead to a decrease in hydrophobicity. From 10 to 40 h, the defluorination rate slows, but oxidation continues, further diminishing the hydrophobicity. This study provides an in-depth understanding of the aging mechanisms of free radicals in fuel cells and offers an important theoretical basis for designing durable membrane electrode assembly (MEA) materials.