We report the poly(vinylidene fluoride-co-hexfluoropropylene) (PVdF-HFP) based porous polymer electrolyte membranes, prepared via phase-inversion/solvent-nonsolvent methods, activated with an organic liquid electrolyte ethylene carbonate (EC): propylene carbonate (PC)-NaClO4 for the application in electric double layer capacitor (EDLC). The simple, quick and environment-friendly phase-inversion method, involving condensing steam as non-solvent, has been taken as the optimized process to obtain the porous PVdF-HFP film. The films of porous PVdF-HFP and the electrolyte (after soaking with liquid electrolyte) have been characterized for their morphological/structural aspects, porosity, liquid electrolyte retention, interaction with electrolyte, thermal properties, electrochemical stability and ionic conductivity. A pore-formation mechanism during phase-inversion at 100 degrees C has been proposed on the basis of thermal studies. The electrolyte film has been found to have excellent mechanical flexibility, porosity (similar to 80%), electrolyte retention (similar to 400%), ionic conductivity (similar to 2 mS cm (1) at room temperature), and electrochemical stability window (ESW) of similar to 4.35 V. The EDLC, fabricated with activated carbon electrodes and porous polymer electrolyte, exhibits excellent performance characteristics in terms of the specific capacitance (similar to 150 F g (1), evaluated from EIS), specific energy (similar to 17.7 Wh kg (1)) and specific power (14.3 kW kg (1)). The device shows stable specific capacitance ( after similar to 17% initial fading) and high Coulombic efficiency (over 99%) for similar to 10,000 charge-discharge cycles. (C) 2017 Elsevier Ltd. All rights reserved.