Robust Proton-Exchange Membranes Based on Perfluorosulfonic Acid-Functionalized Poly(phenyl-alkane) and Polyxanthene: Effects of Skeletal Structures on Membrane Properties

Perfluorosulfonic acid-functionalized aromatic polymers are attractive alternatives to commercial Nafion membranes; however, the heteroatoms (O, S, etc.) in traditional poly(arylene ether)s can initiate undesired chemical degradation by radical specie attacks. Herein, two robust proton-exchange membranes (PEMs), PA-BP-PFSA and PX-BP-PFSA, based on perfluorosulfonic acid-functionalized poly(phenyl-alkane) and polyxanthene, respectively, were prepared by copper-catalyzed postfunctionalization of poly(phenyl-alkane) and polyxanthene precursors containing bromine substituents. Molecular simulation results showed that polyxanthene had a higher rigidity than that of poly(phenyl-alkane). Hence, PX-BP-PFSA had higher Brunauer–Emmett–Teller surface area (124 versus 58 m2 g–1) and fractional free volume (0.303 versus 0.228), compared to that of PA-BP-PFSA. The ionic clusters in PA-BP-PFSA were obviously larger than those in PX-BP-PFSA and showed a higher water uptake and swelling ratio. PX-BP-PFSA exhibited higher conductivity than that of PA-BP-PFSA due to its better microporous nanochannels for ion transport. Both PEMs exhibited an excellent oxidative stability, with no noticeable changes in the thermogravimetric analysis and 1H and 19F NMR spectra after immersion in Fenton's reagent for 2 h at 80 °C. This work presents a feasible approach to develop highly robust perfluorosulfonic acid-functionalized PEMs and provides meaningful insights into the structure–property relationship.