Cobalt hydroxide nanoflakes with a maximum specific capacitance of 735 F/g are successfully synthesized by a facile chemical precipitation method. To enhance energy density, an asymmetric-type pseudo/electric double-layer capacitor is considered where Co(OH)(2) nanoflakes and activated carbon act as the positive and negative electrodes, respectively. The electrochemical properties of the two electrodes and the asymmetric supercapacitor are investigated in 2 M KOH aqueous electrolyte. Values for the maximum specific capacitance of 72.4 F/g and specific energy of 92.7 Wh/kg are demonstrated for a cell voltage between 0 and 1.6 V. By using the nanoflake Co(OH)(2) electrode, the asymmetric supercapacitor exhibits high energy density and stable power characteristics. The hybrid supercapacitor also exhibited a good electrochemical stability with 93.2% of the initial capacitance over consecutive 1000 cycle numbers. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3236500] All rights reserved.