Synthesis and characterization of proton-conducting sol-gel membranes produced from 1,4-bis(triethoxysilyl)benzene and (3-glycidoxypropyl)trimethoxysilane

Hybrid membranes using 1,4-bis(triethoxysilyl)benzene and (3-glycidoxypropyl)trimethoxysilane have been synthesised by polymerization of epoxy groups and inorganic condensation of silanol groups. Sulfonation processes of aromatic rings to produce attached SO3H groups are applied to provide proton conductivity. Thermal analysis shows a high water adsorption capacity combining SO3− and silanol groups. The measurement of conductivity shows a general increase with temperature, and stabilization at temperatures above 100 °C. This behaviour suggests the presence of two competing trends, one enhancing (thermal activation) and the other reducing (dehydration) conductivity. The water retention properties provided by SO3− and silanol groups lead to relatively high proton conductivity (maximum values around 8.5 × 10−4 S cm−1) at 100-150 °C.