Three-dimensional NiCo2O4@NiCo2O4 core–shell nanocones arrays for high-performance supercapacitors

The highly ordered three-dimensional hierarchical NiCo2O4@NiCo2O4 core–shell nanocones arrays on nickel foams are synthesized by stepwise hydrothermal synthesis. The unique nanoarchitectures consist of a layer of NiCo2O4 nanosheets well coated on the surface of NiCo2O4 nanocones. When used in supercapacitors, the NiCo2O4@NiCo2O4 core–shell hierarchical nanostructures exhibit a remarkable capacitance of 2045.2 F g−1 at a current density of 1 A g−1, which are better than that of the individual components of NiCo2O4 nanosheets and NiCo2O4 nanocones. Furthermore, the predominant diffusion-controlled storage is revealed by theoretical analysis. An asymmetric supercapacitor device based on the hierarchical NiCo2O4@NiCo2O4 core–shell nanostructure and activated carbon is fabricated and exhibits a desirable high energy densities with a value of 82.95 Wh kg−1 at power density of 0.35 kW kg−1. These results indicate that the as-prepared NiCo2O4@NiCo2O4 are outstanding candidate for electrochemical supercapacitors.