Preparation Of MXene/Molybdenum Oxide Composite Film As Free-Standing Electrode And Its Application In Supercapacitor

Supercapacitors,as efficient and clean low-cost energy storage devices,have the advantages of high power,fast response and long life.However,the problem of low energy density limits its application.Hence,broadening voltage window and increasing specific capacitance is an effective way to improve energy density.Thus,the development of electrode materials and device assembly design are particularly important.This thesis focuses on the preparation of MXene/Molybdenum oxide composite film electrode and its application for supercapacitors.The influence of the type of aqueous electrolyte and the changes of molybdenum oxide content and treatment temperature on the electrochemical performances of electrode materials are systematically explored,and the storage mechanism of electrode and the performance of different types of devices are further analyzed.The main research contents of this thesis are as follows:1)Three different kinds of MXenes,including d-Ti₃C₂T_x,d-Mo₂Ti C₂T_x,d-V₄C₃T_x,were prepared by solid phase synthesis,chemical liquid phase etching and mechanical stripping.Among them,d-V₄C₃T_x MXene shows the best electrochemical performance,in which the specific capacitance is 292.0 F g^-1(2 m V s^-1)in 3 M H₂SO₄,the rate performance can reach86.0%(200 m V s^-1),the capacitive retention rate is 99.6%after 10000 cycles at 10 Ag^-1,and can be stably stored at room temperature for up to 20 days.In addition,assembling d-V₄C₃T_xwith activated carbon（AC）into an asymmetrical supercapacitor d-V₄C₃T_x//AC,achieving a maximum energy density of 11.0 Wh kg^-1 and a maximum power density of 3833.4W kg^-1.2)The N-d-Ti₃C₂T_x/Mo O_x flexible free-standing film was prepared by one-step solvothermal method,and it is found that the energy storage mechanism is dominated by the surface capacitance and diffusion-controlled.The in situ nitrogen-doped d-Ti₃C₂T_x provides the conductive network,while the in situ grown Mo O_x nanoparticles provide the pseudocapacitance,which the synergistic effect of the two improves the electrochemical performance of the N-d-Ti₃C₂T_x/Mo O_x electrode.The specific capacitance of the N-d-Ti₃C₂T_x/50-Mo O_x composite film electrode with the best content is up to 487.1 F g^-1 at 2 m V s^-1,and the capacitive retention rate can still reach 99.2%after 11,000 cycles at 10 Ag^-1.In addition,the N-d-Ti₃C₂T_x/Mo O_x//AC devices deliver a maximum energy density of 14.9 Wh kg^-1and a maximum power density of 4245.5 W kg^-1.3)The free-standing d-V₄C₃T_x/Mo O₃ composite film electrode was prepared by combining hydrothermal method with liquid phase mixing method.The energy storage mechanism of the composite film electrode is mainly dominated by the diffusion-controlled,and it belongs to"battery-type"electrode material.The change of the energy storage mechanism made a further breakthrough in the capacitance of the electrode.The specific capacitance of the d-V₄C₃T_x/Mo O₃ composite film electrode with the optimal content can be up to 583.3 C g^-1(729.1 F g^-1)at 2 m V s^-1.Moreover,the assembled asymmetric supercapacitor（d-V₄C₃T_x/Mo O₃//AC）can drive the alarm clock and light the LED lamp,with a maximum energy density of 22.2 Wh kg^-1,a maximum power density of 5289.9 W kg^-1,and a capacitive retention rate of 97.0%after 10000 cycles at 10 A g^-1.