Needle-like Co₃O₄ Anchored on the Graphene with Enhanced Electrochemical Performance for Aqueous Supercapacitors

We synthesized the needle-like cobalt oxide/graphene composites with different mass ratios, which are composed of cobalt oxide (Co₃O₄ or CoO) needle homogeneously anchored on graphene nanosheets as the template, by a facile hydrothermal method. Without the graphene as the template, the cobalt precursor tends to group into urchin-like spheres formed by many fine needles. When used as electrode materials of aqueous supercapacitor, the composites of the needle-like Co₃O₄/graphene (the mass ratio of graphene oxide­(GO) and Co­(NO₃)₂·6H₂O is 1:5) exhibit a high specific capacitance of 157.7 F g^–1 at a current density of 0.1 A g^–1 in 2 mol L^–1 KOH aqueous solution as well as good rate capability. Meanwhile, the capacitance retention keeps about 70% of the initial value after 4000 cycles at a current density of 0.2 A g^–1. The enhancement of excellent electrochemical performances may be attributed to the synergistic effect of graphene and cobalt oxide components in the unique multiscale structure of the composites