Fabrication and evaluation of inorganic–organic composite protonic conductors using inorganic sols as a dispersoid

Highly proton conductive inorganic–organic composites to be utilized for the membrane of polymer electrolyte fuel cells were fabricated by the sol–gel method using 3-glycidoxypropyltrimethoxy-silane as a starting material. Inorganic sols employed in this study were SiO2, Al2O3 and a mixture of SiO2 and Al2O3. In order to enhance the proton conductivity, silicotungstic acid was added to the solution before the gelation completed. After the fabricated gels were characterized with XRD, SEM and FT-IR, they were examined in terms of electrical conductivity under various conditions, chemical durability against water and methanol as well as mechanical strength. The conductivity as high as 10− 2 S/cm at 100 °C and 90% R.H. was obtained for the sample derived from SiO2 sol (SG) while slightly lower values were obtained for the samples derived from Al2O3 sol (AG) and those from SiO2 and Al2O3 sol (SAG). The enhanced mechanical strength was obtained for AG while SG was rather fragile. Comparing the chemical durability against water and methanol with each other, SAG were superior to SG and AG . As a whole, SAG was thought to be a promising material as a membrane for PEMFC and DMFC.