EDLC Properties Depend on the Diameter of Mass Produced Multi-Walled Carbon Nanotubes
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0963-Q15-03
EDLC Properties Depend on the Diameter of Mass Produced Multi-Walled Carbon Nanotubes Yong-Jung Kim1, Yusuke Abe2, Takashi Yanagiura2, Massaki Kitani2, Tsuyoshi Kodama2, Keita Higuchi2, and Morinobu Endo1,2 1 Institute of Carbon Science & Technology, Shinshu University, Nagano, .380-8553, Japan 2 Faculty of engineering, Shinshu University, Nagano, 380-8553, Japan
ABSTRACT
Mass produced multi-walled carbon nanotubes (MWNTs) have been investigated for their potential usage in electric double layer capacitors (EDLCs). MWNTs of two different diameters have been tested and we have found a diameter dependant variation on the MWNT performance after KOH activation. The capacitance enhancement and specific surface area (SSA) on KOH activation is more drastic for the thicker MWNT. When charging the activated VGCF up to 3.5 V and discharging at a current density of 10mA/cm2, this material exhibits a capacitance enhancement of 30 times (37.2 F/g) when compared to that of the as-grown VGCF (1.2 F/g). Interestingly, for the case of the thinner MWNT (80 nm, so called vapor grown nanofiber, VGNF), selective attack on their amorphous carbon impurities has been observed and confirmed from both SEM observations and Raman spectra. Consequently, these results would enlighten the potential applicability of MWNTs for manufacturing EDLC electrodes, which could enable the lowest production cost among various types of carbon nanotubes. INTRODUCTION Although much work has been dedicated to supercapacitors using carbon nanotubes (CNTs) as electrodes [1-4], the high cost of CNTs’ manufacturing has been recognized as a problematic drawback for their practical applications. Thus, the capacitance behavior two types of MWNTs, which has been manufactured by mass production methods and already are on the market. Mass production will certainly reduce production costs. Unfortunately, the direct application of VGCFs and VGNFs in EDLC electrodes is complicated, since they have quite small specific surface areas (SSA) (VGCF; ca. 9 m2/g, VGNF; ca. 20 m2/g). Therefore, we have tried to activate the nanostructures in order to obtain sufficient specific surface area by using a chemical reagent (KOH). Furthermore, the diameter of these fibers can be controlled by the amount of catalyst added during their synthesis. VGNF has an average diameter of ca. 150 nm, about half that of VGCF, VGNF is ca. 80 nm in diameter. In this report, we show that the structural variations of the MWNTs as a function of KOH addition depend on their diameter are correlated with the capacitance uptake of each sample. EXPERIMENT Two types of multi-walled carbon nanotubes (MWNT), so called VGCF and VGNF were used. They are trademarks of Showa Denko K. K. (SDK). These two fibers are synthesized by
mass production using a floating reactant method [5,6]. The mass production inevitably reduces the production costs. Furthermore, the diameter of these fibers can be controlled by the amount of catalyst added during the synthesis. In order to obtain sufficient specific surface a
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