Stabilities and pore size effect of proton-conducting organic–inorganic hybrid membranes prepared through surface modification of porous glasses

Proton-conducting organic–inorganic hybrid membranes containing sulfonic acid groups as proton donor were prepared from porous glasses and an organosilane. We found that silanol groups on pore surfaces react one-to-one with organosilane molecules and that the pore surface was covered by sulfonic acid groups. Proton conductivity of the hybrid membranes was 1.25 × 10−1 S cm−1 at 140 °C under 100% relative humidity. The conductivity was dependent upon the pore size because of the capillary condensation of water and the friction of water molecules. The membranes were thermally stable up to 140 °C. They were chemically stable in methanol because the framework structure of these membranes consisted of porous inorganic glass.