Ultrahigh energy density asymmetric electrochemical capacitors based on flower-like ZnO/Co3O4 nanobundle arrays and stereotaxically constricted graphene

Abstract

In this study, unique hierarchical flower-like ZnO/Co₃O₄ nanobundle arrays grown on nickel foam have been synthesized via a facile hydrothermal method. The morphology evolution of the ZnO/Co₃O₄ nanobundles arrays for different contents and reaction times was investigated in detail. The hierarchical structures of the ZnO/Co₃O₄ nanobundle arrays have a large contact area with electrolyte, and have the advantage of excellent ion diffusion and good electronic transport. Consequently, when used as supercapacitors, the ZnO/Co₃O₄ nanobundle array electrodes show remarkable specific capacitance of up to 1983 F g⁻¹ at a current density of 2 A g⁻¹ and 833 F g⁻¹ at a higher current density of 20 A g⁻¹, and 84.5% of the specific capacitance was still retained at 10 A g⁻¹ after 5000 cycles. Furthermore, a ZnO/Co₃O₄ NBs-1//stereotaxically constricted graphene asymmetric supercapacitor device was also produced and was shown to exhibit an ultrahigh energy density of 70.4 W h kg⁻¹ at a power density of 779.8 W kg⁻¹. The ZnO/Co₃O₄ nanobundle electrodes display excellent electrochemical performance, which makes them promising electrode materials for practical application in supercapacitors.