Effect of Chemical Treatment of Multi-walled Carbon Nanotubes on the Capacitance of Supercapacitors

In this paper, the effect of different acids on the change of specific capacitance of multi-walled carbon nanotubes was investigated. Fourier transform infrared spectroscopy spectra, which showed the formation of different oxygen-containing groups on the surface of carbon nanotubes in the range of $1000-1750 cm^{-1}$ were presented. Samples of multi-walled carbon nanotubes treated in hydrochloric acid possessed the highest degree of functionalization. MWNTs treated in dilute nitric acid were barely functionalized. It was found that the specific surface area of the studied samples decreased when treated with sulfuric acid, but there was no dependence of the change of specific capacitance on the surface area. The cyclic voltammetry curve of the sample with the the specific capacitance of MWNT samples was the highest at 55 F g-1 when treated with nitric acid. Additional physicochemical analyses need to be done in order to explain the change of specific capacitance of samples treated with nitric acid.