Synthesis of MnO2/short multi-walled carbon nanotube nanocomposite for supercapacitors

• Multi-walled carbon nanotubes are etched in molten nitrate to produce short MWNTs.
• S-MWNTs can form more stable suspensions than did the pristine MWNTs.
• Nano-scaled MnO2 is more effectively dispersed on the surface of the s-MWNTs.
• This microstructure promotes the electrical conductivity of the electrode.
• The electrode exhibits high specific capacitance and a cycle stability.

Multi-walled carbon nanotubes (MWNTs) were selectively etched in molten nitrate to produce short MWNTs (s-MWNTs). MnO2/s-MWNT nanocomposite was synthesized by a reduction of potassium permanganate under microwave irradiation. For comparative purpose, MnO2/MWNT nanocomposite was also synthesized and investigated for its physical and electrochemical performance. Uniform and conformal MnO2 coatings were more easily formed on the surfaces of individual s-MWNTs. MnO2/s-MWNT nanocomposite estimated by cyclic voltammetry (CV) in 0.5 M Na2SO4 aqueous solution had the specific capacitance as high as 392.1 F g−1 at 2 mV s−1. This value was more than 48.9% larger than MnO2/s-MWNT nanocomposite. In addition, MnO2/s-MWNT nanocomposite was also examined by repeating the CV test at a scan rate of 50 mV s−1, exhibiting an excellent cycling stability along with 99.2% specific capacitance retained after 1000 cycles. Therefore, MnO2/s-MWNT nanocomposite is a promising electrode material in the supercapacitors.