Thermally stable and proton conductive ionogel based on Brønsted acidic ionic liquid with the support of silicate network

Abstract

Thermally stable and water-free proton conductor based on Brønsted acidic ionic liquid and silicate network was prepared by sol-gel processing. As a Brønsted acidic ionic liquid, mixture of bis(trifluoromethyl sulfonyl)imide (HTf2N) and 1-(1-ethyl-3-imidazolio)butane-4-sulfonate (eim4S) was employed. The sol-gel process was successfully done, since the ionic liquid worked as acidic catalyst for the dehydration and the condensation reactions of tetramethoxysilane. Although the gel containing equimolar eim4S and HTf2N showed high ionic conductivity, the thermal stability was poor because of sublimation of the HTFf2N. Use of a small excess amount of eim4S effectively suppressed the sublimation of HTf2N. The obtained glassy ionogel showed high degradation temperature reflecting the thermal stability of both the silicate and the ionic liquid. The ionic conductivity reached to 10-3 S cm-1 at 150°C without any humidification. Contribution of protons to the ionic conductivity was confirmed by chronoamperometry and impedance spectroscopy under hydrogen atmosphere. © 2008 The Society of Polymer Science, Japan.