Novel proton conducting membranes based on copolymers containing hydroxylated poly(ether ether ketone) and sulfonated polystyrenes

A novel series of hydrocarbon-based copolymers containing flexible alkylsulfonated groups and hydroxylated poly(ether ether ketone) backbones was designed and prepared as proton conducting membranes. Among the membranes, the membrane SPO₃–(PMS–PSBOS)₂ with the ion exchange capacity 1.70 showed good proton conductivity at 0.137 S/cm at 80 °C, which was two times as much as that of the control membrane SPO. Further, incorporating the sulfonated graphene oxide (s-GO) into SPO₃–(PMS-PSBOS)₂ leads to the composite membrane SPO₃–(PMS–PSBOS)₂–SGO, which exhibited higher proton conductivity compared to Nation 117 and the native membrane SPO₃–(PMS–PSBOS)₂. In addition, the composite membrane SPO₃–(PMS–PSBOS)₂–SGO showed well-defined phase separated structures and high selectivity (1.40 × 10⁵ Ss/cm³), which were about three times as that of Nafion 117 (0.52 × 10⁵ Ss/cm³). These results suggested that these membranes are promising materials for direct methanol fuel cell (DMFC) applications.