Modification of multi-walled carbon nanotubes for electric double-layer capacitors: Tube opening and surface functionalization |
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Authors: | Chi-Chang Hu Jen-Hong Su |
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Institution: | a Department of Chemical Engineering, National Chung Cheng University, Chia-Yi 621, Taiwan b Department of Chemical Engineering, National Cheng Kung University, Tainan 701, Taiwan |
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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 H2SO4 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 H2SO4+HNO3. The temperature-programmed desorption (TPD) data showed that evolutions of CO and CO2 are, respectively, promoted by the application of partial oxidation in air and chemical modification in H2SO4+HNO3. 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). |
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Keywords: | C Thermogravimetric analysis (TGA) D Electrochemical properties D Microstructures |
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