Supercapacitors with solid/gel polymer electrolytes have attracted much attention due to their high reliability, flexibility, facile designing, being separator-free and free from electrolyte leakage and volatilization such that they can meet the increasing demands of practical applications. The present work reports on a functionalized activated carbon (AC) supercapacitor based on novel redox-mediated gel polymer electrolyte, PVA/H3PO4/ionic liquid (1-ethyl-3-methylimidazolium tetrafluoroborate, [EMIM]BF4). The electrochemical properties of this supercapacitor were studied using cyclic voltammetry, galvanostatic charge/discharge and electrochemical impedance spectroscopy techniques with various concentrations of [EMIM]BF4 in PVA/H3PO4 gel polymer electrolyte. The incorporation of [EMIM]BF4 in PVA/H3PO4 electrolyte effectively increased the specific capacitance value due to the improved ionic conductivity and additional pseudo-reaction occurring in the electrode/electrolyte interfaces. The specific capacitance of the supercapacitor using PVA/H3PO4/[EMIM]BF4 (50%) electrolyte showed a maximum value of 271 F g-1 at 0.5 A g-1 discharge current, which is much higher than the bare PVA/H3PO4 (103 F g-1) based supercapacitor. The supercapacitor with PVA/H3PO4/[EMIM]BF4 (50%) electrolyte showed enhanced energy and power density of 54.3 W h kg-1 and 23.88 kW kg-1 respectively. Moreover the device showed comparable specific capacitance retention after 3000 cycles of charge/discharge.