Polymer electrolyte membranes containing a room temperature ionic liquid, 2,3-dimethyl-1-octylimidazolium triflate (DMOImTf) in polyvinylidenefluoride-co-hexafluoropropylene (PVdF-HFP), show conductivity of 0.96 × 10⁻³ S cm⁻¹ at 80 °C. The addition of triflic acid (HCF₃SO₃) increases the conductivity of the polymer electrolytes by providing free H⁺ ions, which is important for their potential use in proton exchange membrane fuel cells (PEMFCs) and other electrochemical devices. Line narrowing observed in the variation of ¹H and ¹⁹F NMR line width with temperature shows that both protons and anions are mobile in these electrolytes. The membranes have been found to be thermally stable up to 200–300 °C. Polymer electrolyte membranes containing the ionic liquid have also been tested in a single cell fuel cell under non-humid conditions and found to be electroactive for hydrogen oxidation and oxygen reduction at platinum electrodes.