Atomistic insights into the degradation of perfluorosulfonic acid membranes: A reactive force field molecular dynamics study

The chemical degradation of perfluorosulfonic acid (PFSA) membranes remains a critical barrier to the commercial viability of proton exchange membrane fuel cells (PEMFCs). This study employs reactive force field molecular dynamics (ReaxFF-MD) simulations to elucidate the atomistic-scale mechanisms of degradation initiated by hydroxyl (·OH) and hydrogen (H·) radicals. It is demonstrated that H· radicals preferentially abstract fluorine atoms from the polymer backbone (-CF₂-) and attack terminal carboxyl groups (-COOH), thereby initiating unzipping reactions that result in chain scission and defluorination. In contrast, ·OH radicals predominantly attack sulfonic acid groups (-SO₃H) and tertiary carbon sites, leading to side-chain cleavage with minimal backbone disruption. Mixed radical environments exhibit synergistic degradation kinetics, wherein ·OH-mediated regeneration of H· radicals substantially accelerate membrane failure. Elevated temperatures further exacerbate degradation by reducing activation barriers and enhancing radical mobility. A fundamental trade-off between dielectric properties and chemical stability is identified: although polar functional groups enhance proton conductivity, they simultaneously introduce sites susceptible to radical degradation. Selective passivation of -COOH groups is shown to significantly enhance durability while retaining high proton conductivity. These insights provide a mechanistic foundation for the rational design of degradation-resistant PFSA membranes.