Fabrication and proton conductivity of sulfonated silica composites prepared by postoxidization of mercaptomethoxysilane

Sol–gel derived organic–inorganic hybrids containing phosphotungstic acid (PWA) have been prepared previously to obtain proton conductive membranes. However, leaking of PWA was a serious problem to achieve the higher proton conductivity. In this study, polyelectrolyte membranes functionalized with sulfonic acid groups were fabricated by the sol–gel method. Proton conductivity measurements were performed on an impedance analyzer at 80°C/95% RH. The functionalized polyelectrolyte membranes exhibited the proton conductivity σ ～ 0.9 (S/cm) which was much higher than the previously reported hybrids containing PWA. Although the hybrids exhibited fairly high proton conductivity irrespective to the catalysts used, that under the low relative humidity strongly depends on the catalysts. Among the hybrids prepared in this study, the membrane synthesized with HCl showed outstanding proton conductive properties even at the low humidity thanks to the proton transport channel formed by the swelling of ionic clusters. This fact was confirmed by measuring the ion exchange capacity, water uptake, swelling rate, Fourier transform infrared spectroscopy, atomic force microscopy, and thermogravimetric analysis. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012