Anthraquinone-2,7-disulphonate (AQDS) added into neutral electrolyte of KNO3 in symmetric active carbon (AC) capacitor was assessed by cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy techniques. The Faradaic redox reactions were diffusion-controlled and the working window could be extended to 1.8 V. During the charging and discharging processes, the redox reactions occurred on the cathode, leading to considerable enhancement of specific capacitance, power density and energy density, which were 225 F/g, 412 W/kg and 21.2 Wh/kg, respectively at a current density of 1.0 A/g for a symmetric AC capacitor in the electrolyte of 1.0 M KNO3 with 0.1 M AQDS. (C) 2014 Elsevier Ltd. All rights reserved.