Electrochemical properties of multi-walled carbon nanotubes treated with nitric acid for a supercapacitor electrode

Abstract

The capacitances of partially oxidized multi-walled carbon nanotubes (MWNTs) electrodes treated with nitric acid were investigated for use as the electrode materials of electric double-layer capacitors (EDLCs). The oxidized MWNTs had a much higher specific surface area, pore volume and average pore width than those of pristine MWNTs. Moreover, functional groups such as hydroxyl, carbonyl and carboxyl groups were observed on the surfaces of oxidized MWNTs. The specific capacitance of the oxidized MWNTs after 3h a nitric acid treatment was 68.8F/g in the highest oxidized state, more than 7 times greater than that of the pristine MWNTs. Further, the capacitance trends apparently follow the change of the zeta potentials, not the surface areas, indicating that this trend depends on the adsorption of electrolytes as compared to the migration path structure. Further, the oxidized MWNT electrode materials showed good long-term stability during repeated cycles and no decay for more than 1000 cycles.