The micropores and surface oxygen functional groups of KOH-activated carbons were respectively extended and desorbed by the gasification of CO2 during the activation process of chars derived from pistachio shells. These activated carbons (ACs) were found to exhibit ideal capacitive performances (i.e., a rectangular shape of CVs at a wide range of scan rates, high power property, and excellent reversibility) in aqueous electrolytes for electric double-layer capacitors. Although the specific capacitance of these ACs measured at a low scan rate (25 mV s(-1)) is decreased with reducing the density of surface functional groups, the ideal capacitive characteristics can be maintained at a much higher scan rate (300 mV s(-1)) when the CO2 gasification time is equal to or longer than 30 min because of the relatively high proportion of mesopores. (c) 2006 Elsevier Ltd. All rights reserved.