Preparation And Exploration Transition Metal Molybdenum-based Compound As Electrode Material For Supercapacitor

Due to unique metallic conductivity,multiple available oxidation states and special geometric structures with weak interlayer Van de Waals coupling,transition metal Mo-based compounds have been notable candidates for electrochemical supercapacitors.In this thesis,MoO₂/MoS₂,MoSe₂,and MoO₃ electrode material were prepared by simple and economical methods.Moreover,MoO₂/MoS₂ and MoSe₂ were firstly served as negative electrode materials for supercapacitor.The detailed microstructure and morphology information these as-prepared samples were conducted by XRD?SEM?TEM?BET and Mapping methods.The corresponding electrochemical performances were collected by cyclic voltammetry?CV?,galvanostatic charge-discharge?GCD?,and electrochemical impedance spectra?EIS?.Finally,the relation between the electrochemical performance and structure was studied.The main research details and results are as follows:First,MoO₂/MoS₂ composite electrode has been successfully prepared via a simple hydrothermal process for the first time.In this processs,?NH4?Mo7O₂4?4H2O,Na2S?9H2O,and NaHB4 served as raw materials.A series of MoO₂/MoS₂ had been prepared by gradually increasing the quantity of Na2S·9H2O.It indicated that a large amount of smooth nanosheets stretched out towards the outside and self-assembled to further forme flower-like icrosphere structure.The MoO₂/MoS₂ electrode material with flower-like microsphere structure accelerated ion diffusion kinetics and electron transport between the electrode surface and the electrolyte.Ascribe to the synergistic effect,including the improved electron conductivity,the coexistence of two energy storage mechanisms,and a stable flower-like microsphere structure,the as-fabricated MoO₂/MoS₂ exhibits a high specific capacitance of 433.3 F g-1 at a scan rate of 5 mV s-1 and a superior cycling stability of 84.41% retention after 5000 cycles compared to that of pure Mo O₂?33.33% retention after 2000 cycles?and pure MoS₂?58.33% retention after 2000 cycles?at a current density of 1 A g-1 in 1 mol L-1 Na2SO4 electrolyte.Second,MoSe₂ was acted as negative electrode material in SCs,which was synthesized via a simple and economical hydrothermal approach and followed by calcining at 500 °C for 3 h in N2 atmosphere.In this processs,?NH4?Mo7O₂4?4H2O,Se,and NaHB4 served as raw materials.The electrochemical performance was evaluated in 1 mol L-1 Na2SO4.Based on research results of Mo O₂ and MoS₂,MoSe₂ used to further evaluate the electrochemical performance of molybdenum-based compound.Benefits from the stable cockscomb-shaped structures and a good electrical conductivity,MoSe₂ electrode material displays a high rate capability of 75.6%.Moreover,the aqueous asymmetric supercapacitor MoSe₂//AC has been assembled using as prepared MoSe₂ as the negative electrode and SHAC as the positive electrode.MoSe₂//AC shows a high cell voltage of 0¹.9 V,outstanding specific capacitance of 62.08 A g-1 at 1 A g-1,high energy density of 31.1 Wh kg-1,and superior cycle stability with 94% capacity retention even until 6000 cycles.Third,MoO₃ electrode materials were successfully synthesized via one-step facile hydrothermal processs using Na2MoO4?2H2O and HNO₃ served as raw materials,deionized water as solvent.In this processs,the concentration of nitric acid has been control to adjust the pH of reactant solution.Our results have shown that the concentration of nitric acid has great influence on the the crystal orientation of ?-MoO₃.The MoO₃ possesses 531.85 F g-1 at a current density of 1 A g-1 and the specific capacitance retained ⁹6 % after 3500 cycles.Moreover,the aqueous asymmetric supercapacitor of MoO₃//HNC-IPNs has been assembled,which exhibited high specific capacitance of 54.72 F g-1 at 1 A g-1 at a broad cell voltage of 0².0 V.The energy density and power density was superior to traditional AC//AC symmetry supercapacitor.