Proton exchange membrane fuel cells (PEMFCs) are one of the most promising clean energy technologies converting hydrogen energy to electric power. In this study, a protonconducting electrolyte based on a CsHSO4/TiP2O7 composite membrane and operating at > 150 degrees C was fabricated using the vacuum infiltration method and characterized. The electrical properties were investigated in the high temperature range of similar to 110-190 degrees C, in a dry atmosphere, using an impedance analyzer. The analysis of the resultant phase relationship showed that the composite membrane exhibited the same major peaks as each individual material (TiP2O7 and C5HSO4) without any secondary phase. The relative density of the infiltrated C5HSO4/TiP2O7 composite membrane increased up to 96.76%, indicating that most of the pores present in the initial TiP2O7 supporting matrix were infiltrated with C5HSO4. It was consistent with the result of scanning electron microscopy. Moreover, the composite membranes exhibited low ionic conductivities in the low-temperature region, but at similar to 140 degrees C, the ionic conductivities significantly increased because of the superprotonic phase transition of CsHSO4. The maximum conductivity (similar to 2.38 x 10(-3) S/cm) was achieved at 190 degrees C under a dry Ar atmosphere. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.