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.