Steric attenuation of interchain electronic coupling enables anion-exchange membranes with antioxidative properties

Radical-triggered oxidative chain scission of poly(aryl piperidinium) aromatic backbones poses a severe durability challenge for anion-exchange membranes applied in electrochemical devices. Here we report a rigid aromatic molecular-strut strategy that suppresses radical degradation through two complementary antioxidative pathways: electronic shielding against hydroxyl radicals and radical-triggered in-situ crosslink reinforcement. Rigid biphenyl struts anchor to quaternary ammonium sites and disrupt conjugated aggregation to dilute backbone π-electrons. Such structural regulation lifts the backbone oxidation potential by 160 mV, which raises the energy barrier for electrophilic ·OH attack. Beyond electronic shielding, biphenyl struts undergo irreversible radical-mediated oxidative dimerization to generate in-situ covalent crosslinks that dynamically strengthen polymer networks. This dual mechanism, combining electronic passivation with radical-induced crosslinking, enhances oxidative stability by 240% under accelerated Fenton conditions, as measured by retention of mechanical integrity. This work establishes a molecular-level approach to engineering antioxidant anion-exchange membranes, providing a molecular design strategy for long-lived ion-conducting electrochemical membranes.