Proton exchange membrane (PEM) fuel cells operating at elevated temperature, above 120 degrees C, will yield significant benefits but face big challenges for the development of suitable PEMs. The objectives of this research are to demonstrate the feasibility of the concept and realize [acid/ionic liquid/polymer] composite gel-type membranes as such PEMs. Novel membranes consisting of anhydrous proton solvent H3PO4, the protic ionic liquid PMIH2PO4, and polybenzimidazole (PBI) as a matrix have been prepared and characterized for PEM fuel cells intended for operation at elevated temperature (120-150 degrees C). Physical and electrochemical analyses have demonstrated promising characteristics of these H3PO4/PMIH2PO4/PBI membranes at elevated temperature. The proton transport mechanism in these new membranes has been investigated by Fourier transform infrared and nuclear magnetic resonance spectroscopic methods. (C) 2007 Elsevier B.V. All rights reserved.