Preparation, characterization and electrochemical properties of porous NiO/NPC composite nanosheets

We present a facile combined hydrothermal and calcination method to prepare porous nickel oxide/nanoporous carbon (NiO/NPC) composite nanosheets. The material is characterized by powder X-ray diffraction (XRD), scanning electronic microscopy (SEM), transmission electron microscopy (TEM) and high-resolution TEM (HRTEM), X-ray photoelectron spectrometer (XPS), as well as N₂ sorption analyses. Cyclic voltammetry (CV) and galvanostatic charge-discharge tests are performed and indicate that the NiO/NPC possesses superior pseudocapacitive performance with the specific capacitance value of 1337 F g^-1 at the current density of 2 A g^-1 using as the electrode material. The specific capacitance value of 457 A g^-1 can be obtained at the high current density of 10 A g^-1 showing its high rate performance. The material exhibits good cycling stability by retaining 95% of the max capacitance after 500 cycles of continuous charge-discharge processes. Adding NPC in the synthetic process not only changes the elemental composition, but also leads to more Ni³⁺ ions and abundant pores in the texture of the NiO/NPC material, which provides high electron conductivity and fast ion transport, enhances the rate performance of the NiO/NPC electrode, and stabilizes the active material.