Proton conducting inorganic-organic matrices based on sulfonyl- and styrene derivatives functionalized polycondensates via sol-gel processing

Proton conducting inorganic-organic hybrid polymer electrolytes were developed in the last decade based on sulfonated, methacryl and epoxy functionalized alkoxysilanes for thin film cells [Electrochim. Acta 45 (2000) 137]. To improve the electrochemical stability of the materials for applications like polymer electrolyte membranes for direct methanol fuel cells, the less stable methacryl and epoxy alkoxysilanes of the former test system [Electrochim. Acta 45 (2000) 137] were replaced by styrene derivative functionalized alkoxysilanes. These alkoxysilanes were synthesized with a new modified Grignard reaction. The sol-gel materials were prepared in a two-step reaction: first, an alkoxysilane containing a sulfonated group and an alkoxysilane containing at least a nitrogen heterocycle, an amine group or a sulfonamide group were separately hydrolyzed and co-condensed each with one half of the amount of a styrene derivative functionalized alkoxysilane. Then, these two co-condensates were mixed. After evaporation of the solvent, the resin was cast in Teflon(R) moulds or applied on a substrate as a film and finally organically crosslinked via UV and/or thermal curing. The influence of the sample composition on the conductivity and the mechanical properties was studied. Conductivities of 3 x 10(-3) S cm(-1) at room temperature were obtained for membranes free of water, whose precursor composition consists of 60% sulfonated alkoxysilane, finally mixed with 2 mol imidazole per mol -SO3H. If the imidazole is exchanged by water (max. 15 mass% absorption within membrane), the membranes show conductivities up to 8 x 10(-3) S cm(-1) at room temperature. A thermal stability of the inorganic-organic matrix of up to 180 degreesC (< 5% weight loss) was measured by thermo-gravimetric (TG) analysis. (C) 2003 Elsevier Science Ltd. All rights reserved.