Effects of Adsorbed Water on Proton Conduction in Antimonic Acid

Abstract

Effects of adsorbed water on the proton conduction in antimonic acid are discussed on the basis of complex impedance analyses (Fig.1) as well as water sorption isotherms. It was possible to separate the resistivity associated with the intergranular contact from those associated with the bulk and outer surface of individual granules by applying a Cole-Cole plot technique to the samples equilibrated at various water vapor pressures at 60°C (Fig.2). Comparison of these results with those obtained for a Cs⁺-exchanged sample (Fig.4) evidences estimation that proton conduction through the bulk (channels) is more important than or at least comparable with that through the outer surface, depending on the water vapor pressure (Fig.5). The water sorption isotherms (Fig.6) indicate that water is sorbed in to the channels of antimonic acid to far larger amounts than onto the outer surface. The protonic conductivity increased first with increasing amounts of sorbed water, while no further increase was observed after condensation of water in the channel began. Activation energies for conduction (Fig.9) suggest that the proton conduction mechanism may change from a hopping type to a Grotthus type with an increase in the amounts of adsorbed water.