Preparation And Supercapcacitive Propertiesof Graphene Composites

In this work, the graphite oxide was prepared by a modified Hummers method. By using the graphite oxide as precusor, the graphene/Ni(OH)2 and graphene/Mn O2 composites were obtained by hydrothermal methods respectively. The production were charaterized by X-ray diffraction, Field emission scanning electron microscopy, Infrared spectrum, Laser Roman and Thermogravimetric analysis, the composites were used as active materials to prepare supercapacitor electrode, their electrochemical properties were tested by cyclic voltammetry and chronopotentiometry. The results showed that the composites showed better electrochemical properties than the pure graphene and metal oxides.The detailed works are as follows:(1) The research of optimal experimental conditions of the graphite oxide: the graphite oxide was made in concentrated sulfuric acid and potassium permanganate system using graphite as the precusor. The oxidation time at low, medium and high temperature was changed respectively. The results showed that the high temperature oxidation time had a greater influence on the structure of graphite oxide, and the optimal oxidation time is 2 h at 0℃, 0.5 h at 35℃ and 15 min at 95℃.(2) The graphene/Ni(OH)2 composites were prepared by hydrothermal method. The influences of the mass ratio of graphite oxide to Ni(OH)2 and the addition of hydrazine hydrate on the electrochemical properties of graphene/ Ni(OH)2 composites were studied. When the mass ratio of graphite oxide to Ni(OH)2 was 1: 1, the obtained graphene/Ni(OH)2 composites exhibited the best electrochemical performance. The moderate amount of hydrazine hydrate was benefit to the improvement of electrochemical performance. The specific capacitance of the graphene/Ni(OH)2 composites was 1200 F/g at the current density of 200 m A/g. Under the current density of 10 A/g, the energy density was 32 Wh/Kg, and the power density was 2723.5 W/Kg. The composite also exhibited good cycling stability with a capacity retention of 80.4% after 1000 cycles at 5 A/g.(3) The graphene/Mn O2 composites were prepared by hydrothermal method. The optimum reacting conditions for Mn O2 and the appropriate mass ratio of graphite oxide to Mn O2 were studied. The pure α-Mn O2 nanoparticles were prepared under the condition of that the molar ratio of potassium permanganate to manganese acetate was 5: 1. When the mass ratio of graphite oxide to Mn O2 was 1: 10, the obtained graphene/ Mn O2 composites exhibited the best electrochemical performance. The specific capacitance of the graphene/ Mn O2 composites was 173.8 F/g at the current density of 100 m A/g. Under the current density of 500 m A/g, the energy density was 12.3 Wh/Kg, and the power density was 250 W/Kg.