Graphene and activated carbon-wrapped and Co3O4-intercalated 3D sandwich nanostructure hybrid for high-performance supercapacitance

A graphene/Co3O4/activated carbon (GCA) hybrid with excellent electrochemical properties for supercapacitance was successfully fabricated via a simple two-step hydrothermal method. The as-synthesized hybrid was examined by transmission electron microscopy (TEM), X-ray diffraction (XRD), and electrochemical characterization. The results confirmed that Co3O4 particles were homogeneously distributed between the graphene and activated carbon layers. The GCA 1 : 9 capacitor (GC : AC = 9 : 1) showed the best electrochemical property compared with other hybrid capacitors. The specific capacitance of the GCA 1 : 9 hybrid capacitor is 564 F g−1 with activated carbon (AC) covering the outside of the graphene/Co3O4 (GC) layers. The specific capacitance of the GCA 1 : 9 was improved by 53.26% compared with the GC composite capacitor (368 F g−1) at 50 mA g−1 in 7 M KOH. The GCA 1 : 9 also exhibits outstanding cycling property with 90.43% capacitance retention over 10 000 cycles at a current density of 20 A g−1. Moreover, it also achieved a high energy density of 35.7 W h kg−1 at a power density of 235.5 W kg−1, demonstrating that it is a promising candidate for supercapacitance.