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

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.