The influence of aluminum substitution on the proton conductivity of BPO4

The proton conductivity (sigma) of aluminum boron phosphate was measured us ing impedance spectroscopy It was found to be inversely related to the Al/B ratio and calcination temperature, and drastically increased with adsorbed water content. The water assisted conductivity of low aluminum Al-BPO4 was registered to be approaching as high as 10(-2) S cm(-1). At the same time partial replacement of B with Al in boron phosphate substantially enhanced its stability in aqueous surrounding. H-1-, P-31-, Al-27- and B-11 MAS-NMR evidenced that proton conduction occurs through partly and/or completely hy drolyzed species associated with phosphorus. It was assumed that Al additio n suppresses the formation of completely hydrolyzed species and thereby inc reases the solid inertness towards water.