Medium temperature range characterization as a proton conductor for phosphosilicate dry gels containing large amounts of phosphorus

Proton conductivities of phosphosilicate dry gets derived from tetraethoxysilane (TEOS) and H3PO4 increased with an increase in the P/Si mole ratio from 0.5 to 1.0 and tended to level off at 1.0-1.5. The dry gel powder pellets with a P/Si mole ratio of 1.0 showed a high conductivity of 1 x 10(-2) S cm(-1) even after keeping under the atmosphere at 150 degreesC and 0.4% relative humidity (R.H.) for 400 min, Si5O(PO4)(6) crystals and highly condensed phosphates, both of which were formed in the gels during the heat treatment process at 150 degreesC, were readily hydrolyzed. The hydrolyzed species like isolated phosphoric acid and a structural unit with Si O-P OH groups permits the gels to retain high proton conductivity even at temperatures in the medium range with low humidity owing to the good affinity with adsorbed water. (C) 2001 Elsevier Science Ltd. All rights reserved.