Polyaniline-based supercapacitor modified by the addition of an electrochemically active compound (hydroquinone, HQ) into the electrolyte (H2SO4) was investigated. The electrochemical properties of the supercapacitor were evaluated by cyclic voltammetry, galvanostatic charge-discharge, electrochemical impedance spectroscopy technique, and cycle life test. It was found that the supercapacitor exhibited an outstanding specific capacitance value of 584 F g(-1) at the current densities of 0.5 A g(-1), which was significantly greater than that of the original supercapacitor (403 F g(-1)) without adding HQ. The good performance for the supercapacitor was due to the capacity storage mechanism combination of the electrical double layer capacitance and Faradaic pseudocapacitance by HQ in the electrolytes. Furthermore, cycle life test performed showed good stability with retention of the initial capacitance values of 67% after 5000 cycles at a current density of 0.5 A g(-1). The Coulombic efficiency of the cell was close to 100% throughout the experiment. (C) 2013 Elsevier Ltd. All rights reserved.