Epoxy-polystyrene-silica sol–gel membranes with high proton conductivity by combination of sulfonation and tungstophosphoric acid doping

New hybrid electrolytes based on 2-allylphenol (AP), (3-glycidoxypropyl) trimethoxysilane (GPTMS) and tetraethoxysilane (TEOS) have been synthesized by sol–gel method and organic polymerisation. Proton conductivity has been endowed on the base of three strategies: a high concentration of hydroxyl groups from the inorganic component, SO3 − groups through sulfonation of phenyl rings, and incorporation of tungstophosphoric acid (PWA). The system AP–GPTMS–TEOS doped with PWA allows to obtain homogeneous, flexible, transparent and crack-free membranes after sulfonation of phenyl rings from AP. Membranes characterization includes degree of sulfonation, ion-exchange capacity, water uptake and proton conductivity. TGA–DTA analysis shows that the hybrid membranes are thermally stable up to 190 ◦C. Chemical stability of hybrid membrane against sulfonation and doping processes was demonstrated by FTIR and UV–vis-NIR. The membranes present a high ion-exchange capacity, similar to the Nafion®, and water absorptions below 10%. Conductivities around 10−3 S/cm have been obtained at 40 ◦C and 65% relative humidity and 3×10−3 S/m at 110 ◦C and 100% RH. These results show that this new kind of hybrid membranes possess good mechanical properties, high thermal and oxidative stability and high proton conductivity, making them an alternative to be used as electrolytes up to 150 ◦C in PEM fuel cells as well as for lower temperatures and humidity (40 ◦C, 65% RH).Peer reviewe