Sythesis And Supercapacitor Properties Of Nickel-Salt/Graphene Electrode

Supercapacitor is a kind of new-style energy storage between capacitor and batteries. In recent year, it have attracted remarkable interest and have been applied to microelectronic device, power supply of the large electrical equipment, power source for electric vehicle, owing to their high power densities, long-term cycling stability, and fast charge/discharge rates. Supercapacitors, also known as electrochemical capacitors, are mainly composed of three parts: the electrode materials, the electrolytes and the membranes. Among the electrode materials, transitional metal oxides as electrode materials have many advantages, such as low cost, environment friendly, resource-rich. Meantime, graphene as electrode materials also show excellent electrical conductivity and superior chemical stability. In this work, we demonstrate the synthesis of composites of transitional metal oxides/hydroxide composited with graphene, and research the structure and capacitive performance of composites. The main content is as following:(1) The NiMoO4 nanorods were synthesized by a microwave- reflux method, ammonium molybdate and nickel acetate as raw material, Ethylene glycol and deionized water as mixed solvent and urea as precipitator. Through the control of reaction time we have gained different structure of NiMoO4. The XRD, Raman, SEM, and electrochemical investigation show NiMoO4 as supercapacitor electrode can reach high specific capacitance and good structure with excellent electrochemical performance.(2) The preparation and characterization of NiMoO4-rGO. During the microwave reflection, the mesoporous NiMoO4 nanorods grew on the surface of reduced graphene oxide. The NiMoO4-rGO composite exhibited high performance as an electrode material for supercapacitors, with the specific capacitance reached 1274 F/g at a current density of 1 A/g, which is higher than that of pure NiMoO4(800 F/g). NiMoO4-rGO can retain about 81.1% of its initial capacitance after 1000 charge/discharge cycles. The enhanced electrochemical performance of NiMoO4-rGO is mainly ascribed to the mesoporous NiMoO4 nanorods with large specific surface area, as well as high coupling with conductive rGO.(3) The asymmetrical-supercapacitor electrochemical behaviors were investigated by cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy with Ni MoO4-rGO as positive electrode and NG as negative electrode. Owing to the outstanding capacitive behavior of NiMoO4-rGO, the asymmetric device exhibited a high energy density of 30.3 Wh/kg at a power density of 187 W/kg.(4) 3D honeycomb structure of Ni(OH)2-Co(OH)2-rGO were prepared by a green and fast microwave-assisted method. The electrochemical test showed that the specific capacitance of Ni(OH)2-Co(OH)2-rGO reached to 1650 F/g at current density of 1 A/g. Moreover, the specific capacitance of the electrode still contain 900 F/g at current density of 20 A/g. Besides, the Ni(OH)2-Co(OH)2-rGO electrode also showed a good cycle life. The good electrochemical performance of composites is mainly due to synergetic effect with graphene as conductive substrates and honeycomb structure of composites.