Phosphosilicate Gels as a Solid State Proton Conductor at Medium Temperature and Low Humidity.

Abstract

Phosphosilicate (P2O5-SiO2) gels with a P/Si molar ratio of 1.0 heat-treated at 150°C were found to retain a high conductivity of 1.5×10-2S·cm-1 even after holding at a temperature of 130°C at a relative humidity of 0.7% for about 400 min. On the other hand, the conductivity of the porous silica gels impregnated with 5M H3PO4 largely decreased from 1×10-2 to 6×10-6S·cm-1 during holding under the same conditions for about 400 min. The difference in the changes of conductivities between phosphosilicate gels and H3PO4-impregnated porous silica gels with holding time indicates that the former can retain larger amounts of adsorbed water at 130°C than the latter. Condensed structural units with Si-O-P-OH groups in the phosphosilicate gels are expected to enhance the retention of the adsorbed water in the gels aiid improve the proton conductivity even at relatively high temperatures and low humidity conditions.