A Fresh Perspective on Accelerated Degradation Studies for Proton Exchange Membranes

Proton exchange membrane (PEM) water electrolysis is a promising technology for sustainable hydrogen production, but its long-term viability is limited by membrane degradation. PEM degradation is commonly attributed to radical attacks initiated by Fenton reactions, where hydrogen peroxide reacts with transition-metal cations to produce radicals. These can chemically degrade the ionomer, deteriorating proton transport. Ex situ Fenton tests expose membranes to high concentrations of Fe^(2+) and H_2 O_2 to mimic years of chemical damage in days, but the harsh conditions can yield degradation pathways differing from those in operation. To investigate these discrepancies, long- and short side chain PEMs were examined under ion-exchange Fenton conditions. A multi-technique approach linked chemical, morphological, and functional changes across multiple length scales to underlying mechanisms. Results indicate chemical degradation occurs without significant preferential bond cleavage, suggesting uniform polymer breakdown, where the rate depends on the polar side chain structure. In contrast, morphological degradation, previously attributed to radical attack, originates from internal oxygen accumulation via secondary Fenton reactions. These insights underline the limitations of conventional ex situ protocols and establish guidelines for more realistic accelerated degradation tests for PEMs and related polymer electrolytes.