Operation of PEFC using composite sheets composed of phosphosilicate gels and thermally stable organic polymers

Thermally stable, flexible, and proton conductive composite sheets have been prepared from phosphosilicate (P2O5-SiO2, P/Si = 1 in mole ratio) gel powder and several kinds of organic polymers. The organic polymers examined were polyimide (PI), polyamideimide (PAI), polyvinylidene fluoride (PVdF) and styrene-ethylene-butylenes-styrene elastomer (SEBS). PI and PAI effectively improved the chemical durability of the composite sheets by depressing the leaching of phosphoric acid from the gel. PVdF and SEBS provided the composite sheets with an excellent flexibility. Fuel cells using the membrane electrode assembly (MEA) composed of the composite sheet as an electrolyte and Pt-loaded carbon paper sheets as electrodes operated at temperatures in the range from room temperature to medium temperatures (∼ 150 °C).