A chemical vapor deposition employed for growing secondary carbon nanotubes (CNTs) decorated with primary multi-walled CNTs was investigated. N-2 physisorption indicated that the introduction of secondary nanotubes improves both of specific surface area and pore size distribution. The electrochemical behavior of the carbon electrodes in H2SO4 was examined using ac electrochemical impedance spectroscopy. Equivalent circuit analysis indicated that the presence of secondary nanotubes not only reduces the equivalent series resistance but also improves the specific double-layer capacitance. There is ca. 204% capacitance increase achieved through the introduction of secondary nanotubes. (C) 2007 Elsevier B.V. All rights reserved.