Covalent immobilization of perfluorophenylphosphonic acid to simultaneously achieve high stability and proton conductivity for high-temperature proton exchange membrane

Phosphoric acid (PA) leakage and mechanical instability in high-temperature proton exchange membranes (HT-PEMs) remain challenges. In this work, through molecular structure design, a novel tetraamine monomer (PyTAB-5F) was synthesized and used to develop a polybenzimidazole containing perfluorophenyl and pyridine units (5FPBI). Via the Arbuzov reaction, a phosphonated polymer (P–5FPBI) with robust C–P bonds was formed, enabling covalent anchoring of phosphonic acid groups. The acidity of the phosphonic groups was enhanced by the strong inductive effect of adjacent fluorine atoms, allowing them to function as intrinsic proton conductors. These groups can form a stable hydrogen-bonding network with absorbed PA, thereby facilitating proton transport while improving the PA retention capability of the HT-PEMs. The optimized composite membrane (OPBI/P–5F-15%) achieved a peak power density of 757 mW cm −2 at 180 °C and demonstrated exceptional operational stability over 140 h, with a voltage decay rate of only 51.88 μV h −1 . This work provides a molecular engineering strategy for developing HT-PEMs with high performance.