Functionalized Carbon Nanotube Supported By Nickel Nanowire Array with Improved Rate Capability for High Power Electrochemical Capacitors
In current study, f-CNTs are made by refluxing CNTs in concentrated HNO3-H2SO4 (1:3 v/v). 0.5mg/ml f-CNT dispersion in water and electrophoretic deposition(EPD) are used to coat the surface of nickel foils with f-CNT (f-CNT/foil). Nickel nanowires were grown inside the pores of a polycarbonate filter with 13 mm diameter and 400nm pore size using electroplating for 25 min at 1.5 volts. Then, the filter was removed by chloroform to yield free standing nanowires on the nickel substrate. f-CNTs were coated onto the nanowires (f-CNT/nanowire) by similar EPD method.
Specific capacitance of 210 F/g of CNT at 1 mV/s scan rate in cyclic voltammetry test is achieved with f-CNT/foil electrode. CV test results show 60% capacity drop in f-CNT/foil electrode when the scanning rate was increased from 1 to 50 (mV/s) while capacitance drop is about 90% for nickel in the same scanning rate window. As a result, f-CNT/foil electrode shows a better rate capability in comparison with plain nickel electrode. Furthermore, Internal resistance of the f-CNT/foil electrode is measured with electrochemical impedance spectroscopy (EIS) and EIS results show the internal resistance is below 10 ohm. f-CNT/nanowire electrode is expected to provide even better rate capability behavior, thanks to larger contact area between CNTs and nickel, which makes the electron transport path shorter.
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