Proton conductivity of sulfonic acid functionalised mesoporous materials

A detailed comparison of the proton conductivity of three highly ordered mesoporous silica host materials with large inner surface (Si-MCM-41, Si-SBA-15, Si-SBA-16) functionalised with sulfonic acid groups, which were obtained by anchoring and oxidation of thiol groups, is presented. The samples were characterised by X-ray diffraction, nitrogen adsorption, electron microscopy, FT-infrared spectroscopy and TGA/DTA measurements. The proton conductivity is deduced from impedance spectra taken in the temperature range 60–140 °C. All materials show strong dependence of the proton conductivities on the relative humidity, the degree of functionalisation and the pore geometry parameters. Whereas Si-SBA-16 composite materials are poor proton conductors due to the non-directed cubic 3D pore arrangement, functionalised Si-SBA-15 and Si-MCM-41 with hexagonal 1D pore channels exhibit promising proton conductivities at temperatures above 100 °C. For Si-MCM-41 the higher water storage capability is of additional advantage.