Preparation And Electrochemical Properties Of Metal Oxide/Sulfide （TiO₂,SnO₂,MoS₂） Based Composite Electrode Materials

Metal oxides and sulfides have a wide range of applications in the field of electrochemistry,such as anode materials for lithium-ion batteries,electrocatalysts for hydrogen evolution reactions,etc.However,their electrochemical performance is unsatisfactory due to the factors such as few exposed sites and large volume expansion.The published literature has shown that an effective strategy to improve the electrochemical performance of metal oxides/sulfides is to form nanocomposites with graphene,reduced graphene oxide,and other substances,especially nanocomposites with heterostructures.In this dissertation,various nanocomposites of TiO₂,SnO_2,and Mo S₂ were synthesized and used as anodes in lithium-ion batteries,and sodium-ion batteries,or electrocatalysis in hydrogen evolution reactions with significantly improved electrochemical properties.To improve the capacity and cycle stability of TiO₂-based anode materials,Antimony-Titanium dioxide/carbon nanocomposite Sb-TiO₂/C was prepared by a combined method of electrospinning and calcination.It can directly serve as a self-supporting anode in lithium-ion and sodium-ion batteries without using any conductive agent,dispersant,and current collector.Electrochemical tests demonstrate that the electrode material exhibits long cycle life and high specific capacity in both.Its specific capacity can remain 291 m Ah·g^-1after 500 charge-discharge cycles in lithium-ion batteries at the current density of 500 m A·g^-1,while 163 m Ah·g^-1 after300 charge-discharge cycles in sodium-ion batteries.This excellent electrochemical performance originates from the Sb element in the nanocomposite and its unique anatase/rutile heterostructure,porous and interdigitated nanofibrous structure,active sites introduced by self-doped N element,and High stability of the nanocomposite.This work will pave a new road for the design and development of TiO₂-based anode materials,and the synthesized Sb-TiO₂/C nanocomposite will become a promising TiO₂-based anode material.SnO₂ nanorod-graphene nanocomposites with anchored and sandwiched structures（A-Sn G and S-Sn G）were successfully prepared by hydrothermal method and annealing method.The diffusion behavior of Li⁺in two SnO₂ nanorod-graphene composites was revealed by in-situ transmission electron microscopy.The two nanocomposites exhibit different Li⁺diffusion behaviors during the lithiation process.In A-Sn G,Li⁺diffuses in straight lines or zigzags,while in S-Sn G,Li⁺diffuses in all directions.The interface effect between Graphene and SnO₂ nanorods and the dislocations induced during the discharge process provides a fast Li⁺diffusion channel,which promotes the rapid lithiation kinetics,leading to the excellent electrochemical performance of LIBs.These findings could guide researchers to design more promising SnO₂-based hybrid electrodes.To gain an in-depth understanding of the role of heterointerfaces in the hydrogen evolution reaction,the author constructed Mo S₂-graphene nanocomposite（Mo S₂@r GO）through a simple hydrothermal reaction.In the hydrothermal reaction,Mo S₂ arrays were vertically grown on reduced graphene oxide nanosheets,and the Mo-O-C heterointerfaces emerged simultaneously.Electrochemical tests show that the overpotential of the nanocomposite electrode is 239 m V at a current density of 10m A cm^-2,which is superior to that of pure molybdenum dioxide（400 m V）and pristine reduced graphene oxide（>600 m V）.By X-ray absorption spectroscopy（XAS）analysis and DFT theoretical calculations,it is found that the Mo-O-C heterointerface greatly enhances its catalytic activity for hydrogen evolution reaction.This work can not only guide researchers to design better Mo S₂-based hydrogen evolution catalysts but may also provide a new way to optimize the catalytic activity of hydrogen evolution reactions by tuning the heterointerface.