An inorganic-organic hybrid of phenylsilsesquioxane-silica (PhSiO3/2-SiO2) nanoparticle was prepared by sol-gel process, and a high proton-conducting electrolyte was synthesized by surface-sulfonation of phenyl groups of the particles. Chlorosulfonic acid was used as a sulfonation agent. The PhSiO3/2-SiO2 particles are chemically stable as well as flexible. The proton conductivity of the pelletized sample reached about 10(-2) S/cm at 80 degrees C and 80% relative humidity (RH). The open circuit voltage (OCV) of the single cell prepared using the pelletized sample as an electrolyte for a H-2-air fuel cell increased with increasing the RH of the cell. The maximum power density of similar to 40 mW/cm(2) and OCV of 0.9 V was obtained at 80 degrees C and 95% RH. (c) 2008 Elsevier B.V. All rights reserved.