Proton conductivities of sol–gel derived phosphosilicate gels in medium temperature range with low humidity

Phosphosilicate gels derived from tetraethoxysilane (TEOS) and H3PO4 with a P/Si mole ratio of 1.0 retained a high proton conductivity of 1.5×10−2 S cm−1 during the keeping at 130 °C and 0.7% relative humidity for about 400 min. The presence of water molecules with good affinity for gel matrix, which was confirmed from the thermal analysis, permits the phosphosilicate gels to maintain high proton conductivities at that temperature with low humidity. Formation of SiOP bonds was observed from 31P NMR spectra for the gels after a heat treatment at 150 °C. The structural units with SiOPOH groups are expected to enhance the retention of the water molecules and thus improve the proton conductivity of the gels even in the medium temperature range with low humidity.