Supported and free-standing sulfonic acid functionalized mesostructured silica films with high proton conductivity

摘要

Sulfonic acid functionalized silica films with 2D-hexagonal mesostructures of various channel sizes are prepared in a one-step synthesis. A successful combination of in situ oxidation of a mercapto-functionalized silane with an evaporation induced self-assembly (EISA) process in the presence of amphiphilic block copolymers allows the formation of a highly structured material with a sulfonation degree of 33%. Analysis of the mesostructure by a combination of XRD, grazing-incidence small-angle X-ray scattering (GI-SAXS), and TEM shows that 2D-hexagonally ordered mesostructured films are obtained by optimization of the surfactant to silica precursor ratio. The tuneability of the mesochannel size is demonstrated by the use of three different surfactants. The complete oxidation of the mercapto group to sulfonic acid is confirmed by Fourier transform infrared spectroscopy (FTIR). The thermal stability of the material is investigated by coupled thermogravimetric analysis, differential temperature analysis, and mass spectrometry (TGA-DTA-MS). Alternating current (AC) impedance analysis of humidified samples shows high proton conductivity of up to 0.18 Scm-~1 at 60 °C and 95% relative humidity.