Research On The Synthesis And Electrochemical Properties Of Zinc Tungstate And Corresponding Composite Electrode Materials

As an efficient and green energy storage,supercapacitors have shown great potential in many fields.The emergency of supercapacitors has helped to solve the problems of how to use energy efficiently,broaden the scope of new energy and reduce environmental pollution.Thus,it is essential to research supercapacitors thoroughly.ZnWO₄ is of immense potential for electrode materials,which possesses unique advantages of ternary metallic oxides,excellent conductive performance,and is very suitable for application of high performance supercapacitors.The performance of supercapacitors is extensively determined by the properties of electrode materials.Therefore,studying the modification of electrode materials of supercapacitors is of vital.This thesis mainly focused on ZnWO₄ and ZnWO₄'s nanocomposite materials.Their microstructure and electrochemical performance were characterized.The effects of electrode materials'microstructure and chemical component on electrochemical performance were analyzed,which provides the basis for electrode materials'microstructure design and performance optimization.Thus,higher performance electrode materials for supercapacitors can be expected to obtain.The main research contents are as follows:?1?One-dimensional ZnWO₄ nanorods were successfully synthesized under hydrothermal conditions by adjusting the pH value of reaction solution,and it is concluded that weak alkaline reaction environment is most suited to get uniform-distributed and regular-shaped ZnWO₄ nanorods.In addition,through the introduction of nickel foam as current collector substrate material,ZnWO₄ nanoflake arrays were obtained.Electrochemical measurements reveal that the electrochemical performance is greatly improved by introducing the current collector substrate material.ZnWO₄ nanoflake arrays on nickel foam exhibited an areal capacitance of 1.37 F/cm² at2 mA/cm²,and excellent cycling stability?92.5%of areal capacitance remained after2000 cycles at 20 mA/cm²?.?2?ZnCo₂O₄@ZnWO₄ core/shell nanowire arrays were prepared via a facile two-step hydrothermal method,which composited electrochemical active nanomaterial ZnWO₄ with core material ZnCo₂O₄ nanosheet arrays on nickel foam.Due to the synergy effect and unique core-shell nanostructure that extremely facilitate the contact between electrolyte ions and eletrodes,the as-prepared ZnCo₂O₄@ZnWO₄ core/shell nanowire arrays were demonstrated higher areal capacitance of 3.10 F/cm² at the current density of 2 mA/cm² more than twice as much as ZnCo₂O₄,and remarkable capacitance retention of 99.4%after 2000 cycles at 20 mA/cm².?3?Based on the substrates of NiCo₂O₄ nanostructure arrays on nickel foam,NiCo₂O₄@ZnWO₄ core/shell nanowire and nanosheet arrays were synthesized by being composited with ZnWO₄ and controlling the morphology of NiCo₂O₄.The influence of microstructure'diversity on electrochemical performance was discussed.BET test shows that core/shell nanosheet arrays structure is of high specific surface area(131.2m² g^-1),and presents mesoporous structure.Moreover,all-solid-state supercapacitors were assembled by the electrodes of NiCo₂O₄@ZnWO₄,and a series of electrochemical performances were characterized.NiCo₂O₄@ZnWO₄ core/shell nanosheet arrays exhibit the better electrochemical performance.A maximum energy density of 28.46 Wh kg^-1was obtained at a power density of 0.79 kW kg^-1,and 97.5%of initial specific capacitance could be maintained after 5000 cycles.Finally,a red light emitting diode was successfully lighted by the all-solid-state supercapacitors connected in series as power source,which indicate hybrid NiCo₂O₄@ZnWO₄ core/shell nanosheet arrays can be promising electrode materials for supercapacitors'practical application.