One-step green synthesis of graphene/ZnO nanocomposites for electrochemical capacitors

A facile, green and efficient approach consisted of a novel liquid phase exfoliation and solvothermal synthesis method has been adopted to prepare graphene/ZnO nanocomposites as electrode material for electrochemical capacitors. Highly pristine graphene was produced from mild sonication treatment of raw highly pyrolytic graphite in a solution at a proper ratio of ethanol and water. The X-ray diffraction (XRD) analysis revealed the formation of pure ZnO structure from the zinc nitrate hexahydrate precursor during solvothermal synthesis. The surface characteristics and elemental composition of the nanocomposites have been studied by means of field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS) and transmission electron microscope (TEM). The electrochemical properties of the graphene/ZnO nanocomposites were examined by cyclic voltammetry (CV), galvanostatic charge–discharge tests and electrochemical impedance spectroscopy (EIS). The graphene/ZnO nanocomposites displayed an improved capacitive performance of 236 F/g at a scan rate of 10 mV/s, excellent cyclic performance, and an average energy density of 11.80 W h/kg. The improved electrochemical performance of the nanocomposites can be ascribed to the high electrical conductivity of the synthesized pristine graphene and the good electroactive property of ZnO.