Inorganic-Based Proton Exchange Membranes for H2/O2 Fuel Cells

Abstract

The sol-gel method was applied to prepare proton exchange membranes. The proton exchange membrane fuel cells have attracted significant attention because of their ability to produce high energy without emission of harmful pollutants. The main technology of the fuel cells is to prepare the proton exchange membranes and Nafion-based perfluosulfonated ionomers have received consideration as possible electrolytes due to their high proton conductivity at room temperature. Despite this, some problems arise because of their thermal and chemical degradation, and stable materials are desired to be developed. We have proposed the sol-gel technique for the preparation of high proton-conducting membranes and successfully prepared inorganic and inorganic–organic hybrid membranes exhibiting high proton conductivities compared to that of perfluosulfonated ionomers. Metal alkoxides such as Si(OC2H5)4 and PO(OCH3)3 are hydrolyzed, followed by heating at 400–600°C to form porous glasses, in which the water molecules are absorbed. The proton conductivities were investigated relating with the pore structure, adsorbed water molecules and glass compositions. The conductivities follow the Arrhenius equation and the activation energy decreases with increasing the logarithm of the product of proton and water concentration. The proton conductivities increase with increasing the content of water and hydroxyl groups and reach ~10−2 S/cm at room temperature. Further inorganic–organic hybrids doped with the heteropoly acids and ionic liquids are prepared to increase the proton conductivities at high temperature under anhydrous condition.