Synthesis and characterization of proton-conducting materials containing dodecatungstophosphoric and dodecatungstosilic acid supported on silica

Solid electrolytes formed by different amounts of phosphotungstic acid (PWA) and silicotungstic acid (SiWA) in silica gel have been prepared and characterized. XRD, IR and DTA analyses performed on the samples in powder form revealed the existence of an interaction between the heteropoly acids and the support. This interaction was stronger in the case of SiWA than in the case of PWA. Nevertheless, the samples with 15 and 30 wt.% of SiWA, which presented higher interaction with the support, and for this had engaged more protons to this end, showed higher proton conductivities with respect to the samples at the same loading of PWA. This fact was justified by the higher number of protons possessed by the SiWA molecules. An increase of proton conductivity was also observed when increasing the relative humidity (r.h.) of atmosphere over the samples and the heteropoly acid lending. This was because at higher r.h., the number of water molecules in the material increased, thus allowing an easier movement of protons and, at higher heteropoly acid loading, because the concentration of mobile protons increased. (C) 1999 Elsevier Science S.A. All rights reserved.