Activated carbon nanotubes (ACNTs) with high surface area have been successfully prepared from carbon nanotubes by KOH activation for electric double layer capacitors. The microstructure of the ACNTs was characterized by TEM and nitrogen adsorption isotherms. The electrochemical capacitive performances of the ACNTs in 1 mol•L^－1 Et₄NBF₄/PC electrolyte were evaluated with cyclic voltammetry (CV), galvanostatic charge/discharge and ac impedance spectroscopy, etc. When the amount of activation agent increased, or the activation temperature rose, or the activation time was prolonged, the specific surface area and the capacitance of the ACNTs all showed an increasing tendency. The surface area of the ACNT sample prepared by KOH activation with KOH/C ratio of 3∶1 at 800 ℃ for 4 h reached 663 m²•g^－1, three times larger than that of the pristine non-activated carbon nanotubes. Its specific capacitance reached 57.2 F•g^－1, three times as large as that of the non-activated carbon nanotubes. It was found that there was a linear dependence of the capacitance on their BET surface area for activated carbon nanotubes.

Key words: electric double layer capacitor, carbon nanotubes, activation, specific surface area, specific capacitance