Abstract
Multi-walled carbon nanotubes (MWCNTs) obtained opening the closed ends and using surface functionalization by means of a combination of partial oxidation in air and chemical modifications are characterized systematically in 0.3 M H 2 SO 4 between 0 and 1.0 V, and these nanotubes were planned to be used as electrode materials in electric double-layer capacitors (EDLCs). Opening of MWCNTs, clearly observed by means of transmission electron microscopy (TEM), can be easily achieved by the partial oxidation in air through a seven-step temperature program identified by thermogravimetric/differential thermal analyses (TG/DTA). An increase in 175% specific capacitance is obtained for the MWCNTs, partially oxidized in air and chemically modified in H 2 SO 4 +HNO 3 . The temperature-programmed desorption (TPD) data showed that evolutions of CO and CO 2 are, respectively, promoted by the application of partial oxidation in air and chemical modification in H 2 SO 4 +HNO 3 . The above increase in specific capacitance for modified MWCNTs is attributed to an obvious increase in the BET surface area (double-layer capacitance) and the density of oxygen-containing surface functional groups (pseudocapacitance). © 2007 Elsevier Ltd. All rights reserved.