Preparation Of Based Ni₃S₂ Nanocomposites And Their Application In Supercapacitors

Supercapacitors have drawn much attention as a kind of new and green energy storage device with high power density,fast charge-discharge capacity,and long service life.Electrode material research is one of the important ways to improve the performance of supercapacitors.Among them,Ni₃S₂ is an outstanding electrode material with providing high electrochemical activity and pseudocapacitance through the fast redox reaction on the surface or near surface location of the electrode.However,a single electrode material is not entirely satisfactory no matter in morphology,conductivity and electrochemical performance.Therefore,it is necessary to design and synthesize novel desirable nanostructures or different types of nanomaterial composite based on Ni₃S₂.It can improve the energy storage and conversion of the device by using the intrinsic characteristics of each material to complement each other and achieve synergistic effects in the electrochemical performance.In this work,we have investigated the influence of the concentration of raw materials on the morphology and electrochemical performance for Ni₃S₂.And the effect of H₂O₂ about the growth mechanism of Ni₃S₂ was discussed.The double shell NiMoO₄@C@Ni₃S₂ core-shell nanowire arrays were designed and synthesized and the attenuation mechanism of the materials after consequent charging-discharging cycles was explored.The main contents of this thesis are as follows:（1）Ni₃S₂ nanosheet-rod arrays directly grown on Ni foam are synthesized by one step hydrothermal method using Ni foam as nickel source and collector,and the concentration of sulfur source is optimized.What’s more,it is found that H₂O₂ has a certain impact on the morphology of Ni₃S₂.Different morphologies of Ni₃S₂ are prepared under a series of different concentrations of S₂O₃^2-.The electrochemical performances of these materials are evaluated by cyclic voltammetry,galvanostatic charge–discharge and electrochemical impedance in a three-electrode system.The result shows that the Ni₃S₂ nanorods coated with homogeneous nanosheet displays excellent electrochemical properties when the amount of Na₂S₂O₃ is 1.2 mmol.It shows larger areal capacitance of 4.74 F cm^-22 at a current density of 15 mA cm^-2,above 85.7%of its original capacitance retention after 3000 cycles.A sandwich-type solid-state asymmetric supercapacitor is assembled with Ni₃S₂ nanosheet-rod arrays as a positive electrode and active carbon as a negative electrode in PVA/KOH gel electrolyte.The device displays excellent energy density and power density.It obtains a maximum energy density of 1.166 mWh cm^-3 at a power density of 14.99 W cm^-3and a high power density of 90.1 W cm^-3 at an energy density of 0.927 mWh cm^-3.（2）The fabrication of double-shell NiMoO₄@C@Ni₃S₂ core/shell nanowire arrays growth on Ni foam is achieved through hydrothermal and electrodeposition methods.The NiMoO₄,NiMoO₄@C and NiMoO₄@C@Ni₃S₂ are also synthesized to explore the performance advantages of the double-shell core/shell nanomaterial.The electrochemical properties of these materials are tested in a three-electrode system.NiMoO₄@C@Ni₃S₂ exhibits outstanding electrochemical performance:the areal capacitance is 5.409 F cm^-2 at a current density of 10 mA cm^-2 and the capacitance remains about 78.95%of the initial value after 3000 cycles of charge-discharge.In addition,the structure and morphology of the material after electrochemical reaction are characterized and the mechanism of capacity fading is analyzed.A sandwich-type solid-state asymmetric supercapacitor is assembled with PVA/KOH gel electrolyte.And the device displays excellent energy density and power density with a high energy density of 1.166 mWh cm^-3 at a power density of 14.99 W cm^-3.