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.