This work demonstrates a novel electrochemical procedure to enhance the specific capacitance (CS) of activated carbon (AC) in organic electrolytes for the electrical double-layer capacitors (EDLCs). An irreversible oxidation process which provides pseudocapacitance occurs on AC when the electrode potentials are more positive than 0 V in the propylene carbonate (PC) electrolyte containing 1 M tetraethylammonium tetrafluoroborate (TEABF(4)). This modification has been optimized by repeating 5 times of 100 charge-discharge cycles between -1.9 and 0.5 V in the fresh electrolyte. The surface of modified AC has been identified to contain N, B, and F, probably resulting from the repeated anchoring of electrolyte. An asymmetric supercapacitor (ASC) consisting of the above modified-AC positive electrode and an as-received AC negative electrode shows the specific energy and power of 18 Wh kg(-1) and 6.5 kW kg(-1) at 5 A g(-1) with a cell voltage of 2.6 V. This ASC also shows excellent charge-discharge stability in TEABF(4)/PC from the 1.9% decay in the cell capacitance after 10,000-cycle stability test at 5 A g(-1) between 0 and 2.6 V, revealing superior performances. (C) 2014 The Electrochemical Society. All rights reserved.