Comparison of structure and proton conductivity of phosphosilicate gels derived from several kinds of phosphorus-containing compounds

Proton conductive phosphosilicate gels have been prepared from tetraetboxys ilane (TEOS) and various kinds of phosphorus-containing compounds such as o rthophosphoric acid (H3PO4), triethylphosphate (PO(OEt)(3)) and 2-(di-ethox yphosphoryl)ethyltriethoxysilane (DPFS) by the sol-gel method. Proton condu ctivities of all the phosphosilicate gets increased with an increase in rel ative humidity, indicating that continuous paths suitable for fast proton c onduction were formed in the gets due to the adsorption of water. The H3PO4 -derived gel heat-treated at 150 degreesC showed a high conductivity of 3 X 10(-3) S cm(-1) even in a dry atmosphere of 20% relative humidity at room temperature. In the case of heat treatment at 600 degreesC, the conductivit y of DPTS-derived phosphosilicate gels was higher than those of the H3PO4-d erived and PO(OEt)(3)- derived ones. The decrease in the amount of isolated phosphoric acid and the formation of crystalline phases in the phosphosili cate gels lowered the proton conductivity. (C) 2001 Elsevier Science B.V. A ll rights reserved.