Preparation and Electrochemical Performance of Nitrogen-DopedNanocarbon Coated MnO Composites

Assisted by electrostatic force, MnO₂ nanowires were hybridized with hydrochloric acid treated melamine (H-melamine), with mass ratios of H-melamine to MnO₂ nanowires of 1\:1, 3\:1 and 5\:1, respectively, and then was annealed to fabricate nitrogen-doped nanocarbon coated MnO (MnO@N-C) composites. The phase composition, microstructure and electrochemical performance of the composite were studied. The results show that the MnO₂ nanowires and surface-coated H-melamine were transformed to MnO and nitrogen-doped carbon materials, respectively, by annealing, and the obtained MnO@N-C composite showed beadlike morphology. When the mass ratio of H-melamine to MnO₂ nanowires was 3\:1, the composite achieved the best electrochemical performance, exhibiting high specific capacitance of 1 050 F·g^-1 at the current density of 1 A·g^-1 and capacitance retention of 75% after 6 000 charge/discharge cycles at 3 A·g^-1 current density. The zinc-ion hybrid supercapacitor assembled with the composite as cathode and activated carbon as anode could operate in the voltage window of 0-2.0 V, and showed an energy density of 72 W·h·kg^-1. After 5 000 cycles at the current density of 3 A·g^-1, the supercapacitor still maintained 88% of the initial specific capacitance.