Study On The Preparation And Electrochemical Properties Of Molybdenum-based Low-dimensional Oxides And Sulfides

Supercapacitors have the advantages of high-power density,long service life and high safety.They are high-efficiency energy storage devices that can be quickly stored and released.Therefore,supercapacitors have broad application prospects in the fields of portable electronic products,hybrid or pure electric vehicles and smart grids.In the past ten years,in addition to extensive research on graphene,mixed transition-metal oxides,and transition metal dichalcogenides have received extensive attention in the energy field as important industrial materials.In this thesis,one-dimensional V_0.13Mo_0.87O_2.935 nanowires were prepared by one-step hydrothermal method,different concentrations of MoS₂ nanosheets and MoS₂@ACF composites were prepared by one-step microwave method.Their structures and morphology were determined by X-ray diffraction(XRD),scanning electron microscope(SEM),transmission electron microscope(TEM),and X-ray photoelectron spectroscopy(XPS).Finally,the electrochemical properties of V_0.13Mo_0.87O_2.935,different concentrations of MoS₂ and MoS₂@ACF composites were characterized by cyclic voltammetry,galvanostatic charge-discharge,electrochemical impedance spectroscopy,and cycle stability.The main works of this paper are summarized as follows:(1)The one-dimensional V_0.13Mo_0.87O_2.935 nanowires were successfully prepared by one-step hydrothermal method,and the structure and morphology of the samples were characterized by XRD,SEM,TEM,XPS and N₂ adsorption-desorption isotherm analysis.The results show that the sample is a uniform one-dimensional polycrystalline structure with a diameter of 20-30 nm and a length greater than 10?m.In addition,it was used as a supercapacitor electrode material and electrochemically tested in a three-electrode system using 1 M Na₂SO₄ as an electrolyte.The results show that when the current density is 2 A g^-1,it has a higher specific capacitance of 385.2 F g^-1.When the current density was increased from 2 A g^-1 to 10 A g^-1,it exhibited excellent rate performance of 91.5%and outstanding cycle stability.After 10000 CV cycles,the capacity retention rate was 97.6%.(2)MoS₂ nanosheets were prepared by one-step microwave method by changing the concentration of the reactants.The structure and morphology were characterized by XRD,SEM,and TEM.Studies have shown that MoS₂ prepared with 0.0075 mol Na₂Mo O₄is a uniform sheet structure.As the concentration of the reactants increases,the MoS₂nanosheets self-assemble and form nanospheres.In addition,different concentrations of MoS₂prepared were used as electrode materials for supercapacitors,and electrochemical tests were carried out with 1 M KCl as an electrolyte under a three-electrode system.The results show that the specific capacitance of MoS₂ prepared by 0.0300 mol Na₂Mo O₄ is83.36 F g^-1 at a current density of 0.5 A g^-1,indicating that the specific capacitance of the material needs to be improved.The cycle stability of MoS₂ prepared by 0.0300 mol Na₂Mo O₄ was tested.After 6000 cycles of voltammetry,the capacity retention was 76.2%,indicating its electrochemical properties need to be further improved.(3)In order to improve the electrochemical performance of MoS₂,based on the previous chapter,MoS₂@ACF composites were prepared by one-step microwave method by changing the concentration of reactants.The structure and morphology of the samples were characterized by XRD,SEM,and XPS.Studies have shown that MoS₂@ACF composites prepared with 0.0075 and 0.0150 mol of Na₂Mo O₄ have MoS₂ nanosheets embedded or attached to the ACF surface.MoS₂@ACF composite prepared by 0.0300 mol Na₂Mo O₄,MoS₂ nanosheets agglomerated on the surface of ACF.MoS₂@ACF composite prepared by 0.0500 mol Na₂Mo O₄,the surface of ACF is uniformly and densely covered by MoS₂.The XPS characterization of MoS₂@ACF composites prepared with 0.0500 mol Na₂Mo O₄ showed that the MoS₂@ACF composite consisted of four elements:C,Mo,S and O.In addition,different concentrations of MoS₂@ACF composites and pure ACF were used as electrode materials for supercapacitors,and electrochemical tests were carried out with 1 M KCl as electrolyte under a three-electrode system.The results show that the specific capacitance of MoS₂@ACF composite prepared by 0.0300 mol Na₂Mo O₄ is492.36 F g^-1 at a current density of 0.5 A g^-1,after 9500 cycles,the specific capacitance retention rate of was 97.5%.Compared with the pure MoS₂ and ACF electrode materials the specific capacitance and cycling stability of MoS₂@ACF composite materials was significantly improved.