Activated carbon aerogels (ACAs) with hierarchically porous structures and high specific surface area have been prepared via CO2 and KOH activation processes. The pore structures of ACAs are characterized by N-2 adsorption/desorption and scanning electron microscopy. The experimental results show that the ACAs contain three types of pores: micropores with diameters below 2 nm, small mesopores with diameters from 2 to 4 nm and large pores or channels with diameters over 30 nm. The typical sample ACAs-4, which possess pore volume of 2.73 cm(3) g(-1) and specific surface area of 2119 m(2) g(-1), exhibits high specific capacitances of 250 F g(-1) and 198 F g(-1) at the current densities of 0.5 A g(-1) and 20 A g(-1) respectively in 6M KOH aqueous solution. Furthermore, the resultant ACAs electrode materials also exhibit high power density, good cycling stability and long lifetime. With these features, ACAs are expected to be promising electrode materials for electrical double layer capacitors. (C) 2012 Elsevier Ltd. All rights reserved.