Electrochemical electric double layer capacitors (EDLC) known as supercapacitors are used for high power density, long cycle life and good reversibility of charge/discharge processes^[1]. Recent years, many Schiff base transition metal composites acting as an electroactive electrode material deposited on carbon nanotubes(CNTs) have been researched^[2]. However, the CNTs tend to be random orientation, twining round and cross linked. So it urgently need to be addressed. In this paper, a given mass of NH₄BF₄ was added to CNTs and the electrode was prepared by the homodispersion of the raw support material in N-methyl- 2-pyrrolidone (NMP) through sonicating. The slurry was coated on a Ti sheet with the coating mass of 0.3 mg. The electropolymerization of Ni(salen) on the resulting electrode was conducted in a closed three-electrode compartment cell adopted chronoamperometry method. The introduction of NH₄BF₄ to the CNTs with a specific percentage (5wt. %, 10wt. %, 15 wt. %), and the modified samples were named as NBF5, NBF10, NBF15 respectively and the CNTs without NH₄BF₄ were taken as a control group and named as NBF0. As the cyclic voltammetric data summarized in Table 1, the values of apparent surface coverage(Γ) and doping level(n) of NBF5, NBF10 and NBF15 didn't appear to be much different from those of NBF0. However, the specific capacitance varied a lot. It can be seen that C_m of NBF15 is the most among the samples. Figure 1 depicts the GCD plots of the composite and CNTs at the current density of 1.0 mA cm^-2. CNTs have symmetric change in the charge/discharge process which is the characteristic of high Coulombic efficiency. It is clear that the composites possess longer charge/discharge time than CNTs which indicating that poly[Ni(salen)] contributes the pseudo-capacitance derived from reversible redox switching between neutral and oxidative states on the basis of electric double-layer capacitance of MWCNTs. Because of the introduction of NBF, it became difficult for CNTs to twint together disorderly. And the morphylogy of the electrode support got homogeneous. NBF-containing carbon nanotube could provide basic sites, and consequently improved the deposition of polymer and enhance the performance of the electrode material.

Acknowledgement

This work is financially supported by the National Natural Science Foundation of China (No. 51372021).

References

[1] D. Kaufman, K.L. Hudson, R. Mcclamrock. Science. 343 (2014) 1210–1211.

[2] Y. Zhang, J. Li, F. Gao, F. Kang, X. Wang, F. Ye, J. Yang. Electrochim. Acta. 76 (2012) 1–7.