Silica ionogels for proton transport

Abstract

A number of ionogels – silica–ionic liquid (IL) hybrid materials – were synthesized and studied for their ionic conductivity. The materials are based on a sulfonated IL, 1-methyl-3-(3-sulfopropyl-)-imidazolium p-toluenesulfonate, [PmimSO₃H][PTS], which contains a sulfonic acid/sulfonate group both in the IL anion and in the side chain of the IL cation. By way of the sulfonate–sulfonic acid proton transfer, the IL imparts the ionogel with a high ionic conductivity of ca. 10⁻² S cm⁻¹ in the as-synthesized state at 120 °C and 10⁻³ S cm⁻¹ in the dry state at 120 °C. The ionogels are stable up to ca. 150 °C in dynamic thermogravimetric analysis. This suggests that these materials, which are relatively cheap and easily fabricated, could find application in fuel cells in intermediate temperature ranges where many other membrane materials are not suitable.