The multi-walled carbon nanotube (MWCNT) was treated with HNO3 to increase their surface area and improve their properties. Cyclic voltammetry (CV) was used to evaluate the optimize conditions of the modified MWCNT for the higher specific capacitance. After MWCNT are activated by treatment with 5 M concentration of HNO3 for 12 h, the specific surface area of the MWCNT increases to 145 m(2)/g. The CV performance of the modified MWCNT has shown that the specific capacitance increases from 8.9 to 22.6 F/g. Thus, the modification of the MWCNT improves the surface properties and increases their capacitance for use in energy storage applications. (C) 2011 Elsevier B. V. All rights reserved.