Preparation And Supercapacitive Performance Of Ni And Co Based Binary Metal Oxide Nanocompisites

In recent years,supercapacitors have received more and more attention due to their high power density,excellent cycle performance and fast charge-discharge process.Binary metal oxides are considered as one of the most promising electrode materials for supercapacitors because of their low price,environmental friendliness,high electrochemical activity and high theoretical capacitance.In the present thesis,a series of nickel and cobalt based binary metal oxide nanocomposites have been prepared through hydrothermal,solvothermal and chemical bath deposition method,and the microstructure and supercapacitive performance of the obtained materials have been systematic studied.The main research contents are as follows:Mesoporous NiCo₂O₄ has been prepared by co-precipitation method and heat treatment at low temperature with oxalic acid as the precipitating agent,and the electrochemical properties of the obtained materials are studied.Nickel-cobalt oxalate precursor is completely decomposed at 350 oC and converts to mesoporous NiCo₂O₄ with specific surface area of 151.8 m2/g and the pore size distribution of 4¹0 nm.NiCo₂O₄ electrode exhibits a specific capacitance of 980.6 F/g at a current density of 0.6 A/g in 1M KOH solution.NiCo₂O₄ electrode presents higher supercapacitive performance than NiO and Co₃O₄,which is mainly attributed to the mutual doping between different composite components,improved electric conductivity of electrode material and abundant potential oxidation states.CNTs@MnCo₂O₄ core-shell nanocomposite has been prepared by solvothermal method and low temperature heat treatment using isopropyl alcohol as the solvent.By controlling the reaction time of solvothermal process,the formation mechanism of CNTs@MnCo₂O₄ nanocomposite is discussed.The CNTs@MnCo₂O₄ electrode exhibits a specific capacitance of 1258.5 F/g at a current density of 1 A/g in 1M KOH solution with 91.5% capacitance retention after 3000 cycles.The superior electrochemical performance could be attributed to high specific surface area and the intimate interaction between the CNTs and MnCo₂O₄ nanosheets.Nickel foam supported NiCo₂O₄ nanowires and nanosheets have been synthesized through a simple hydrothermal method.There are many pores on the surface of nanowires and nanosheets.The nanowires show conical structure and the nanosheets are interconnected with each other.The electrochemical studies show that the supercapacitive performance of NiCo₂O₄ nanowires is superior.Then,NiCo₂O₄@NiO,NiCo₂O₄@Co₃O₄ and NiCo₂O₄@NiCo₂O₄ core-shell nanostructures are prepared by the following chemical bath deposition using NiCo₂O₄ nanowire arrays as the core materials.The NiCo₂O₄@NiCo₂O₄ electrode exhibits a specific capacitance of 1480.5 F/g at a current density of 1 A/g in 1 M KOH solution with 90.6% capacitance retention after 3000 cycles.Similarly,nickel cobalt manganese oxide nanosheets have been synthesized by chemical bath deposition.An asymmetric supercapacitor is fabricated by using the nickel cobalt manganese oxide electrode as the positive electrode and activated carbon?AC?as the negative electrode,which exhibits a maximum energy density of 36.4 Wh/kg at the power density of 320 W/kg.NiMoO₄ nanowires,CoMoO₄,NiWO₄ and CoWO₄ nanosheets arrays on foam nickel substrates have been synthesized by a simple one-step hydrothermal method.As the electroactive materials are directly grown on the conductive substrate and the adding of conductive agents and adhesives is avoided,the electrode materials can be fully contacted with the electrolyte and the electroactive materials can be effectively utilized.The electrochemical studies show that the specific capacitance of nickel molybdate and nickel tungstate are higer and the rate capability of cobalt molybdate and cobalt tungstate are superior.An asymmetric supercapacitor is assembled by using the CoWO₄ electrode as the positive electrode and activated carbon?AC?as the negative electrode,which exhibits a maximum energy density of 48.1 Wh/kg at the power density of 365 W/kg.