Sol-Gel Preparation of Fast Proton-Conducting P2O5-SiO2 Glasses

We have investigated the proton conductivities of the sol-gel-derived P2O5-SiO2 glass at −50 to 120°C. The obtained glass is porous, where the surface area, pore volume and pore diameter are 740 m2/g, 0.5 cm3/g and <5 nm, respectively. The freezing temperature of water molecules adsorbed in the pores was −20°C, which is much lower than that of free liquid water due to the quantum size effect of the water confined in the pores. The electrical conductivities followed the Arrhenius equation in the temperatures between −20 and 120°C. Below −20°C, the adsorbed-water molecules were frozen, resulting in a rapid decrease of the proton conductivity. Considering the high conductivity, chemical and thermal stability, this oxide glass membranes have potential for the fuel cell membrane.