Study On Preparation And Electrochemical Properties Of NiO Nanomaterials

As emerging energy devices,supercapacitors(SCs)have attracted tremendous attention owing to their remarkable power density and long cycle life.It is well known that the electrochemical performance of supercapacitors is largely determined by the characteristics of electrode materials.So it is important to develop electrode materials with superior electrochemical performance but at low cost.Among various transition metal oxides,NiO is considered to be one of the most potential materials for supercapacitors due to its high theoretical capacitance,excellent cycling performance,cost effectiveness and environmentally friendly.This thesis takes nickel oxide as the research object.The effects of morphology and doping of other metal elements on the electrochemical properties of NiO electrode materials were investigated.The research contents of this thesis are as follows:1.NiO nanosheets have been synthesized via a facile solvothermal route using water-ethylene glycol as solvent and polyvinyl pyrrolidone(PVP)as surfactant.These NiO nanosheets were interweaved with each other to form hierarchical flower-shaped structures.NiO nanocubes and nanospheres were also obtained through changing the reaction temperature and solvent.NiO nanosheets had the largest specific surface area among the three morphologies.The electrochemical tests were conducted using a three electrode system in 6 mol/L KOH with the as-synthesized NiO as the working electrode.Electrochemical properties were characterized by cyclic voltammetry,galvanostatic charge/discharge measurements,and electrochemical impedance spectroscopy.NiO nanosheets exhibited the highest specific capacitance(402 F/g at current density of 0.5 A/g)and the best rate capability(80.1% capacitance retention from 0.5 A/g to 4 A/g).NiO nanosheets also showed excellent cycle stability,only lost 9.7% after 1000 cycles.2.Lanthanum doped nickel oxide nanomaterials were prepared by a simple solvothermal synthesis method.Through the characterization and analysis of the nano-materials,it can be seen that the morphology and structure of the materials have changed due to the incorporation of different proportion of La.The electrochemical tests were conducted using a three electrode system in 6 mol/L KOH with the as-synthesized La doped NiO as the working electrode.4% La doped NiO exhibited a remarkable specific capacitance of 682 F/g at 0.5 A/g,which was the highest in the tested samples.4% La doped NiO possessd excellent rate capability,83.4% specific capacitance was maintained when the current density increased from 0.5 A/g to 4 A/g.To test the cycling stability of 4% La doped NiO,continuous galvanostatic charge-discharge cycling for 1000 cycles were carried out at 4 A/g.Specific capacitance of 4% La doped NiO only lost 7.4% after 1000 cycles.3.Cobalt doped nickel oxide nanomaterials were prepared via a solvothermal route.The products were characterized by SEM,EDS and XRD.The morphology and structure of the materials changed due to the incorporation of different proportion of Co.The electrochemical tests were conducted using a three electrode system with the as-synthesized Co doped NiO as the working electrode.The results showed that 12% Co doped NiO possessed a remarkable specific capacitance of 606 F/g at 0.5 A/g,which was the highest in the tested samples.12% Co doped NiO had excellent rate capability(83% capacitance retention from 0.5 A/g to 4 A/g).Specific capacitance of 12% Co doped NiO only lost 6.5% after 1000 cycles at 4 A/g,and the capacitance retention rate was still 93.5%.