Inorganic–organic hybrid films using epoxycyclohexylethyltrimethoxysilane and orthophosphoric acid for PEFC operated at medium temperatures

Proton conductive inorganic–organic hybrid films, which show high proton conductivity at temperatures higher than 100 °C with low humidification, have been prepared from epoxycyclohexylethyltrimethoxysilane (EHTMS), 3-glycidoxypropyltrimethoxysilane (GPTMS) and H3PO4 by the sol-gel method. Self-supporting, flexible films with a thickness of about 150 to 300 μm were obtained. The ionic conductivity of the films increased with an increase in the relative humidity and was about 1 × 10− 2 S cm− 1 under 25% relative humidity at 130 °C. For a fuel cell with the hybrid film (P / Si = 1.5) as an electrolyte under H2 and air at 130 °C, 17% relative humidity, the open circuit voltage of the cell was about 0.9 V and a power of about 40 mW cm− 2 was obtained with current density of 110 mA cm− 2. It was also confirmed that the test cell can operate more than 10 h with a current density of 100 mA cm− 2.