Electrochemical behavior of NiO/CNT composite electrodes prepared by electrophoretic deposition and dipcoating method.

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The acid-treated carbon nanotubes (CNTs) were dispersed in isopropanol solution to form homogeneous CNT suspension. The porous CNT film was coated onto the stainless steel substrate by electrophoretic deposition (EPD) in a CNT suspension. The porous CNT electrodes were chemically coated with nickel hydroxide nanoparticles using nickel sulfate solution containing surfactant via a coprecipitation method. The CNT film electrode prepared by EDP was dipped in a solution of 0.05 M nickel sulfate, and then the soaked film electrode was immersed in 0.05 M NaOH solution; finally, the film electrode was rinsed in de-ionized water. These steps were repeated several times to obtain the required amount of nickel hydroxide on the CNT film. After coating, all film electrodes were rinsed several times in de-ionized water and dried at 300oC for 3 h in air to from NiO/CNT composite electrodes. The effects of surfactant on the capacitive behavior of composite electrodes were investigated. SEM (scanning electron microscope) photographs reveal that the nickel oxide nanoparticles were coated on the CNT film, regardless of the surfactant used during the preparation. XRD (X-ray diffraction) patterns reflect that the effect of surfactant on the crystal structure of composite electrode can be negligible; all deposited nickel oxides are cubic nickel oxide. Electrochemical investigations on a number of NiO/CNT composites indicate that a composite prepared by a nickel sulfate solution containing 20 mM CTAB (cetyl trimethylammonium bromide) exhibits high specific capacitance and high cycle-life stability compared with other composite electrodes. This composite electrode has an initial capacitance of 432 F/g, which decreases to 295 F/g (about 68.6 % of the initial capacitance) after 6000 galvanostatic charge/discharge cycles.