Proton-conducting gel electrolyte

Abstract

Proton conduction in solid state xerogels and polymeric gels are reported. Xerogels, doped with known proton conductors, were prepared by “sol–gel” method starting either from inorganic precursor sodium metasilicate (termed as hydrogel) or organic precursor tetraethyl orthosilicate (termed as silica or SiO 2 alcogel). The dopants chosen for the former were NH 4BF 4, NH 4Cl, NH 4H 2PO 4 and N 2H 6SO 4, while for the latter, the dopants used were H 3PO 4, NH 4BF 4, NH 4H 2PO 4 and KH 2PO 4. The SiO 2:H 3PO 4 alcogel gave the highest room temperature conductivity (∼10 −3 S cm −1). Some of the xerogels studied by us were stable even up to 300 °C. Another interesting group of proton-conducting materials discussed in this paper is polymeric gel which was prepared by dispersing PMMA in the liquid electrolyte obtained by dissolving o-, m-, p-hydroxybenzoic acid; o-, m-, p-nitrobenzoic acid and three dicarboxylic acids, viz., oxalic, malonic and succinic acid, in a high-dielectric constant organic solvent. The role of the dissociation constants of the dissolved acids and the interaction of the polymer were discussed. The addition of polymer, inspite of the increasing viscosity, was found to sometimes lead to an increase in the conductivity of liquid electrolyte, which was explained on the basis of a breathing polymer chain model.