In Situ Electrochemical Raman Spectroscopy of Air-Oxidized Semiconducting Single-Walled Carbon Nanotube Bundles in Aqueous Sulfuric Acid Solution

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• 作者：Shin-ichi Ogino ; Takashi Itoh ; Daiki Mabuchi ; Koji Yokoyama ; Kenichi Motomiya ; Kazuyuki Tohji ; Yoshinori Sato
• 刊名：Journal of Physical Chemistry C
• 出版年：2016
• 出版时间：April 7, 2016
• 年：2016
• 卷：120
• 期：13
• 页码：7133-7143
• 全文大小：644K
• ISSN：1932-7455

文摘

In this study, we oxidized approximately 90% semiconducting, highly crystalline single-walled carbon nanotube (hc-SWCNT) bundles in the atmosphere at 450 °C for 30 min to obtain SWCNTs modified with oxygen-containing functional groups and investigated not only the influence of air oxidation on the electrochemical doping of the air-oxidized SWCNT (AO-SWCNT) bundles in aqueous sulfuric acid solution using in situ Raman spectroscopy, but also the relationship between the in situ electrochemical Raman data and the properties of electric double-layered supercapacitors (EDLSCs). By oxidizing the hc-SWCNTs in air, AO-SWCNTs with a small diameter distribution could be prepared. When a negative charge was applied to the AO-SWCNTs used as a working electrode in a three-electrode electrochemical cell for in situ Raman spectroscopy, a large downshift of the G⁺ line of the AO-SWCNTs was observed compared to that before air oxidation. On increasing the ratio of small-diameter nanotubes/total nanotubes, the Raman data obtained in situ revealed that the effect of the weakening of the C–C bond was stronger than that of the renormalization of the phonon energy. In contrast, in the case of applying a positive charge to the AO-SWCNTs, the magnitude of the upshift of the G⁺ line for the AO-SWCNTs was slightly larger than that for the hc-SWCNTs. The influent electric charges per unit mass and the specific capacitances of the AO-SWCNT electrodes for the maximum magnitude of the shift of the G⁺ line (10.7 cm^–1) were 60.1 C/g and 50.1 F/g, respectively, which are larger than those of hc-SWCNT electrodes. In situ Raman spectroscopy is a useful method to simultaneously assess the increase or decrease in the diameter distribution of small nanotubes and the specific capacitances of electric double-layered supercapacitors of chemically functionalized SWCNTs by the magnitude of the shift of the G⁺ line compared to unfunctionalized SWCNTs.