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

摘要

Proton conductivities of phosphosilicate dry gels derived from tetraethoxysilane (TEOS) and H{sub}3PO{sub}4 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 × 10{sup}(-2) S cm{sup}(-1) even after keeping under the atmosphere at 150 ℃ and 0.4% relative humidity (R.H.) for 400 min. Si{sub}5O(PO{sub}4){sub}6 crystals and highly condensed phosphates, both of which were formed in the gels during the heat treatment process at 150 ℃, 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.