Membranes based on phosphotungstic acid and polybenzimidazole for fuel cell application

Composite membranes based on phosphotungstic acid (PWA) adsorbed on silica (SiO2) and polybenzimidazole (PBI) have been prepared and their physico-chemical properties have been studied. The membranes with high tensile strength and thickness of less than 30 μm can be cast. They are chemically stable in boiling water and thermally stable in air up to 400°C. Proton conductivity is influenced by the temperature (range: 30–100°C), relative humidity and PWA loading in the membrane. Maximum conductivity of 3.0×10−3 S/cm is obtained at 100% relative humidity and 100°C with membrane containing 60 wt.% PWA/SiO2 in PBI. Conductivity measurements performed at higher temperatures, in the range from 90°C to 150°C, give almost stable values of 1.4–1.5×10−3 S/cm at 100% relative humidity.