A new ionic liquid gel polymer electrolyte based on hydrophobic ionic liquid 1-ethyl-3-methylimidazolium tris(pentafluoroethyl) trifluorophosphate (EMImFAP) entrapped in poly (vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) copolymer has been prepared for its application as an electrolyte in supercapacitor fabrication. The gel electrolyte film shows excellent thermal stability and remains stable in the same gel phase over a substantially wide temperature range from 5 to 90 degrees C. The gel material possesses wider electrochemical window of similar to 4.4V (-2.2 to 2.2 V) and high ionic conductivity of similar to 2 x 10(-3) S cm(-1) at room temperature. The solid-state supercapacitors have been fabricated with pristine and nitric acid treated MWCNT electrodes using the new ionic liquid gel polymer electrolyte. The performance characteristics of the capacitors have been evaluated by impedance spectroscopy, cyclic voltammetry, and galvanostatic charge-discharge measurements. A substantial improvement in the specific capacitance has been found due to the acid treatment of the MWCNTs. The modified MWCNT electrodes show the maximum capacitance value of similar to 76 Fg(-1), which corresponded to the specific energy of similar to 17.2 Wh kg(-1) and specific power of similar to 18.9 kW kg(-1) of MWCNT with ionic liquid gel polymer electrolyte based supercapacitor cells. The supercapacitor shows good cycling performance with similar to 82% capacitance retention after 10,000 charge-discharge cycles. (C) 2013 Elsevier Ltd. All rights reserved.