Proton Conducting Composites of Heteropolyacid Hydrates (Phosphomolybdic and Phosphotungstic Acids) Dispersed with Insulating Al2O3

Abstract

Composites of heteropolyacid hydrates with insulating Al2O3 as the dispersoid, viz. xPMA + (1 — x)Al2O3 and xPTA + (1 — x)Al2O3, have been prepared and characterised using DTA/TGA, XRD, IR and ion transport measurements. New exothermic peaks in the DTA for the composites with more Al2O3 and the changes in XRD suggest the probable formation of a new interface compound at the Al2O3 interface. The bulk electrical conductivity has been found to depend upon the composition, temperature and relative humidity. The composition versus conductivity isotherm exhibits two maxima at x = 0.8 and 0.6 for the PTA:Al2O3 system and x = 0.7 and 0.5 for the PMA:Al2O3 system. Phenomenologically, this could be either due to the two different thresholds for the two types of mobile species (H+/H3O+ and OH—) or due to the formation of a high conducting interface compound.