High-temperature proton exchange membranes with tunable acidity of phosphonic acid groups by incorporating zwitterionic aromatic moieties

Abstract The electrochemical performance and durability of high-temperature proton exchange membranes (HT-PEMs) are critically influenced by the effective distribution of proton conductors, electrolyte retention, and interfacial compatibility. Here we present three acidic types of proton conductors (covalently bonded PA, ion-pair bonded PA, and free PA) within phosphonated zwitterionic aromatic polymer structure, allowing for the precise regulation of proton conductors distribution to satisfy the performance of HT-PEMs. Covalently bonded PA groups and ion-pair bonded PA function as fixed proton sources, anhydride inhibitors, and free radical scavengers, effectively mitigating the dependence of proton conductivity on free PA. Furthermore, the incorporation of ion pair coordination significantly reduces the proton conductors leaching during operation. By optimizing the ratio of these proton conductors, polyelectrolytes maintain excellent proton conductivity stability and outstanding fuel cell performance. The resulting membrane, with high proton conductivity of 183 mS cm −1 and outstanding peak power densities of 728 mW cm −2 , delivers a low voltage decay rate of only 0.367 mV h −1 over 140 h period at 140 °C, opening up route for high-performance HT-PEM with low PA adsorption (105%) and high PA retention (68%).