The Preparation And Capacitance Properties Of Graphene And Graphene/Nickel Hydroxide Composite Materials

In this paper,graphite as raw material was oxidized to graphite oxide using the Hummers method.Graphene?RGO?and RGO/Ni?OH?₂ composite were obtained by a eco-friendly hydrothermal method at different hydrothermal time,hydrothermal temperature and reactant ratio.And a symmetric capacitor was assembled by using graphene electrode.All samples were tested by electrochemical methods.The test results are as follows:Graphene has good capacitance performance when the hydrothermal time is 6 h and hydrothermal temperature is 200 ?.In 0.1 M KOH solution and at 1.1 A-g^-1 current density,the specific capacitance of RGO is up to 357.1 F.g^-1 between-1?0.4 V.After 2000 times of charging and discharging,the specific capacitance remains 72.4%.RGO/Ni?OH?₂ composite has superior capacitance performance when the hydrothermal time is 6 h,the mass ratio of RGO to Ni?OH?₂ is 1:7 and the hydrothermal temperature is 200 ?.At 20 A-g^-1 current density,the specific capacitance is up to 2210 F-g^-1 between-0.05?0.45 V.After 2000 times of charging and discharging,the capacitance remains 86%,which has superior cycling property.The specific capacitance of symmetric capacitor is 55.2 F-g^-1.The energy density and power density are 11 Wh-Kg^-1 and 3200 W-Kg^-1,respectively.After 2000 times of charging and discharging,the capacitance remains 80%,which has superior cycling property.The structure characteristics of graphene and RGO/Ni?OH?₂ composite were characterized by Fourier transform infrared spectroscopy?FT-IR?,thermogravimetry and differential scanning calorimetry?TGA-DSC?,X-ray diffraction spectroscopy?XRD?and Scanning electron microscope?SEM?.The FT-IR of graphene indicated that graphene was successfully obtained by reducing graphite oxide because of the oxygen-containing functional groups on the graphene almost disappeared and the Ni-OH and Ni-O characteristic peaks of Graphene/nickel hydroxide complexes were obvious.The XRD results further confirmed that graphene was reduced successfully,both graphene and P-Ni?OH?₂ existed in compounds.In SEM images,we could see graphene was very smooth and translucent and nickel hydroxide uniformly covered on the graphene.