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An electrochemical process for modifying the pore-size distribution (PSD) of single-walled carbon nanotubes (SWNTs) is developed. The effect of electrochemical treatment time on the PSD of SWNTs is investigated, and the results show that such treatment provides an effective and controllable method for changing the PSD of SWNTs. In particular, a remarkable volume of the small mesopores in the 3.0-5.0 nm diameter range is increased. The SWNTs treated for 24 h at 1.5 V have a higher specific surface-area (109.4 m(2) g(-1)) and larger volume of small mesopores (0.048 cm(3) g(-1) in 3.0-5.0 nm diameter range), compared with the as-grown SWNTs (46.8 m(2) g(-1) and 0.026 cm(3) g(-1), respectively). The as-grown SWNTs and the electrochemically-treated SWNTs are investigated as electrochemical capacitor electrodes, and it is found that the specific capacitance is increased three-fold after electrochemical treatment. (c) 2006 Elsevier B. V All rights reserved.