Proton-conducting properties of hydrated tin dioxide as an electrolyte for fuel cells at intermediate temperature

Proton conductivity of hydrated tin dioxide (SnO2·nH2O) was investigated at 100–150 °C under water vapor pressure up to 0.5MPa, and was compared with that of hydrated zirconia (ZrO2·nH2O). High proton conductivities above 10−2 S cm−1 were observed in both hydrates at 150 °C under high water vapor pressures. The conductivity decreased with a decrease in water vapor pressure at 130–150 °C, but the decrease of conductivity in SnO2·nH2O was smaller than that in ZrO2·nH2O. The SnO2·nH2O showed a good recovering property of conductivity after drying at 150 °C, which was not observed for ZrO2·nH2O, suggesting the SnO2·nH2O to be suitable as proton-conductive electrolyte for use at intermediate temperature. Films of SnO2·nH2O/polymer composites were prepared, and a high conductivity was observed in SnO2·nH2O/R-epoxy resin.