Electrochemical oxidation of multi-walled carbon nanotubes and its application to electrochemical double layer capacitors

The effect of electrochemical oxidation in 0.2 M HNO3 for multi-walled carbon nanotubes (MWNTs) on the performance of electrochemical double layer capacitors (EDLCs) was studied. Scanning electron microscope and transmission electron microscope images reveal that electrochemical oxidation increases the specific area of MWNTs by cutting off the nanotube tips. Cyclic voltammetry and constant current charging/discharging was used to characterize the behavior of EDLCs of the oxidized-MWNTs in 1.0 M H2SO4. The specific capacitance of the oxidized-MWNTs was remarkably improved. The maximum specific capacitance of 335.2 +/- 13.1 F g(-1) (n = 3) was obtained for the oxidized-MWNTs with open tips, which is I I times than that of normal MWNTs (32.7 +/- 7.1 F g(-1)). Electrochemical oxidation is hence an effective way to improve the performances of the MWNTs electrodes in EDLCs application. (C) 2005 Elsevier B.V. All rights reserved.