Proton Conductivity of Mesoporous Silica Incorporated with Phosphorus under High Water Vapor Pressures up to 150.DEG.C.

Abstract

Silica mesoporous structures incorporated with phosphorus were prepared and their proton conductivity was evaluated at temperatures of up to 150°C under saturated or controlled water vapor pressure. The fixing of phosphoric acid through heat treatment after forming the mesostructure had a limited effect on the improvement in proton conductivity only in a relatively low-temperature region. The incorporation of phosphorus during mesoporous silica formation decreased the surface area but was effective in improving proton conductivity. A sample with a low P/Si atomic ratio of 0.07 showed the highest proton conductivity above 10-2 Scm-1 at 100 to 120°C under saturated water vapor pressure. A sample with a high P/Si atomic ratio of 0.25 showed relatively high conductivities being maintained even at low relative humidity at 150°C. An adequate phosphorus concentration and a large surface area were found necessary for high and humidity-independent proton conductivity in mesoporous silica.