Highly pyrolytic graphite (HOPG) was used as a precursor to produce graphene in an apt ratio of ethanol and water. The as-synthesised graphene was subsequently used to produce graphene-Cobalt oxide (Co3O4) composites via solvothermal method. Morphological and structural characterizations of the prepared composites demonstrated that Co3O4 was successfully formed on the graphene sheet. Electrochemical measurements of graphene-Co3O4 composites from cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy indicated that the mass ratio of graphene to cobalt oxide precursors is crucial to affect their electrochemical performance. The capacitive performance of the graphene-Co3O4 composites electrode prepared at a mass ratio (1:4) exhibited superior specific capacitance of 384 Fig at a current density of 0.3 A/g, with an energy density of 64 Wh/kg and a power density of 103 kW/kg. The electrode also showed good cycling performance, with about 80% retention of the capacitance after 1000 cycles. (C) 2016 Elsevier B.V. All rights reserved.