The NiO electrode materials in electrochemical capacitor: A review

In recent years, nickel oxide has attracted much attention for the supercapacitor application because of the advantages of low toxicity, cheapness and environment friendliness. This review focuses on the performance of nickel oxide and its composites in supercapacitors and their synthesizing strategies. It is concluded that the supercapacitor performance depends on morphologies, surface area, particle size, porosity and crystallinity of nickel oxide materials. Their three-dimensional morphology with porous structures usually presents higher specific capacitance. Compared with pure NiO nanocrystals, NiO-based composites often show higher specific capacitance resulting from the synergetic effects between the components. Furthermore, the strategies for preparing NiO-based materials including hydrothermal/solvothermal methods, electrospinning technique and microwave-assisted method, and the factors affecting their electrochemical performance have also been summarized.