A highly conductive proton exchange membrane for high temperature fuel cells based on poly(5-vinyl tetrazole) and sulfonated polystyrene

• The novel PVTra(SPS)x membranes were prepared.
• The PVTra(SPS)x shows high proton conductivity at high temperature with low humidity.
• The PVTra(SPS)x are flexible and don’t show fragility as the pristine SPS.
• The PVTra(SPS)x retains water vapor facilitating proton conduction.
• A sketch map summarizes the functions of the membrane components in proton conduction.

Poly(5-vinyl tetrazole) (PVTra) with 85% molar content of tetrazole was prepared by [3 + 2] cyclo-addition of polyacrylonitrile (PAN) with sodium azide. The membranes of PVTra(SPS)x were prepared by blending different ratios of PVTra to sulfonated polystyrene (SPS) (SD = 72%). The on-set degradation temperature of the PVTra(SPS)x is above 180 °C. The degradation behaviors related with the acid–base interaction were analyzed. The membranes were confirmed to retain 0–5% water vapor at 80–140 °C in air due to the hydrophily of highly sulfonated polystyrene. The membrane PVTra(SPS)2 shows the proton conductivity of 10− 2 S/cm at 100 °C and even around 4 × 10− 2 S/cm at 120 °C without extra humidity supply and is very promising for high temperature fuel cells with low humidity. The high proton conductivity is ascribed to the unique composition in which the heterocyclic polymer provides the proton motion by construction diffusion and the highly sulfonated polymer retains water vapor to lower the activation energy for proton conduction. The possible proton conduction sketch map is provided.