Proton mobility in tungstic 12-heteropoly acids

The ionic conductivities of heteropoly acids were measured using impedance spectroscopy in the temperature range 15-400 degreesC. The proton migration activation energies were determined. The contents of hydrogen-containing s pecies of tungstic 12-heteropoly acids with a varied number of acid protons -H3PW12O40 . nH(2)O (n = 6.5,23), H4SiW12O40 . nH(2)O (n = 9, 18), and H5Ga W12O40 . nH(2)O (n = 10, 13)-were determined by H-1 NMR and thermogravimetr y. The proton-proton distances in the H2O and H3O+ species of the heteropol y acids were found to depend on their annealing temperature. Tungstophospho ric acid was demonstrated to have an optimal relationship between the stren gths of the H-bonds of acid protons and water molecules and of water proton s to oxygen atoms, so that this acid is a better proton conductor than tung stophosphoric and tungstogallic acids.