Partly nitrogenized nickel oxide hollow spheres with multiple compositions for remarkable electrochemical performance

In order to improve the conductivity of NiO, a simple and effective strategy has been utilized. Here, we synthesized partly nitrogenized nickel oxide hollow spheres and used them as an electrode material of a supercapacitor. It was found that the prepared partly nitrogenized material possessed a mesoporous shell of multiple compositions consisting of NiO, Ni₂O₃, Ni₃N, and N-doped NiO, the latter partly substituted with nitrogen. The first-principles calculations were also employed to investigate the composite structure and the result demonstrated an improved electronic conductivity. The partly nitrogenized NiO spheres acted as a battery-type electrode material delivering a gravimetric specific capacity of 492C g⁻¹ at 1 A g⁻¹ and a long-term stability in a three-electrode system. The assembled hybrid supercapacitor exhibited a maximum capacitance of 121F g⁻¹ at 1 A g⁻¹, a high energy density of 37.8 Wh kg⁻¹ and power density of 37.5 kW kg⁻¹, and high capacitance retention after 5000 charge–discharge cycles. The excellent electrochemical performance indicates that the partly nitrogenized NiO hollow spheres can compare favorably with nanostructured NiO materials composited with carbon nanotubes and reduced graphene oxide for application in energy storage devices.