Proton-conducting gel electrolyte

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 SiO2 alcogel). The dopants chosen for the former were NH4BF4, NH4Cl, NH4H2PO4 and N2H6SO4, while for the latter, the dopants used were H3PO4, NH4BF4, NH4H2PO4 and KH2PO4. The SiO2:H3PO4 alcogel gave the highest room temperature conductivity (similar to10(-3) S cm(-1)). Some of the xerogels studied by us were stable even up to 300 degreesC. 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. (C) 2002 Elsevier Science B.V. All rights reserved.