Enhancement on proton conductivity of inorganic–organic composite electrolyte membrane by addition of sulfonic acid group

A proton-conducting porous silica matrix for composite membranes was prepared by introduction of sulfonic acid groups on the surface. The surface modification of pores in the porous silica membrane was performed by using 3-mercaptopropyltrimethoxysilane (SH oxidation method) or 1,3-propanesultone (direct reaction method). The sulfonated silica matrix exhibited high proton conductivity of 6.0×10−3 S cm−1 at 60 °C under 90% relative humidity. This value was about 400 times higher than that of unmodified silica matrix. The proton conductivity of the composite membrane filled by a proton-conducting gel polymer, 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS), was considerably enhanced by using the sulfonated silica matrix.