Novel organic/inorganic hybrid electrolytes have been designed for high temperature polymer electrolyte fuel cells (PEFCs). The hybrid electrolyte membranes were synthesized from 1,8-bis(triethoxysilyl)octane (TES-Oct) and 3-(trihydroxysilyi)-1-propanesulfonic acid ((THS)Pro-SO3H) via sol-gel process. The membranes with sulfonic acid groups covalently bonded to the silica show higher proton conductivity of 5 x 10(-2) S/cm at 160degreesC than that of previously reported homologous materials containing phosphotungstic acid as acid function. A series of electrodes with different composition of the organic/inorganic nanohybrid materials to the platinum loaded carbon has been prepared in order to elucidate the availability of the electrolytes in the catalyst layer. By optimizing the composition of the nanohybrids, high electrode performance comparable to that using Nafion(R) ionomer has been obtained. The novel organic/inorganic hybrid materials have proved to be a promising material as the ionomer in the electrodes and the electrolyte membranes for high temperature PEFCs. (C) 2004 Elsevier Ltd. All rights reserved.