Novel composite electrolyte membranes consisting of [EMIm](FH)(n)F (EMIm=1-ethyl-3-methylimidazolium, n = 1.3 and 2.3) ionic liquids and fluorinated polymers were synthesized and their physical and electrochemical properties were measured under unhumidified conditions for their application to the intermediate temperature fuel cells. The ionic conductivities of composite membrane, P(VdF-co-HFP)/s-DFBP-HFDP/[EMIm](FH)(2.3)F (1/0.3/1.75 in weight ratio), were 11.3 and 34.7 mS cm(-1) at 25 and 130 degrees C, respectively. The open circuit voltage (OCV) observed for the single cell using [EMIm](FH)(2.3)F composite electrolyte was -1.0 V at 130 degrees C for over 5h. The maximum power density of 20.2 mW cm(-2) was observed under the current of 60.1 mA cm(-2) at 120 degrees C. From the high thermal stability and high ionic conductivity, the fluorohydrogenate ionic liquid composite membranes are regarded as promising candidates for the electrolytes of the unhumidified intermediate temperature fuel cells. (C) 2007 Elsevier B.V. All rights reserved.