Construction,Modification And Investigation Of Supercapacitors Performance For ZIF-67 Derived Carbon Nanotube Matrix Complex Structure

To address energy shortages and achieve carbon peaking and carbon neutrality goals,governments have been investing huge human,material and financial resources to develop clean and sustainable new energy sources.While fossil fuels such as oil,coal and natural gas are gradually replaced by clean renewable energy sources including wind,hydro,geothermal and tidal energy,there is an urgent need to develop efficient and safe energy transition and storage equipments.Supercapacitors have been favored by many scientific researchers because of their advantages such as long cycle stability and high-power density.However,due to the common problem of low energy density,researches are still needed to develop supercapacitor electrode materials with both high-power density and high energy density.As a sub-series of MOFs materials,ZIF-67 not only has the characteristics of high porosity,high specific surface area and aperture control,but also shows the high stability(thermal stability and chemical stability)as inorganic zeolite materials,so it has great potential in energy storage applications.However,owing to the poor conductivity of ZIF-67,its practical application in energy storage is limited.Aiming at this poor conductivity problem of ZIF-67,in this thesis work,Cu-doped ZIF-67 is carbonized to give rise to DCNTs(Dodecahedron Carbon Nanotubes),and with the subsequent treatment involving oxidation,vulcanization and construction of DCNTs@CoNi-LDH core shell structure,the nanocomposites electrodes are produced with excellent electrochemical energy storage performance.The specific work of this thesis is as follows:(1)The transition metal elemental load CNTs and graphite carbon hierarchical network structure(DCNTs)were obtained via carbonization of Cu-doped ZIF-67.Followed by oxidation and vulcanization,Co3O4 and CoSx/Co support CNTs and graphite carbon hierarchical composite structures were constructed,respectively.Proved by various electrochemical characterization methods,oxidation and vulcanization can rectify the shortcomings of DCNTs such as poor electrochemical activity and low specific capacitance,bringing about electrode materials with high energy density.(2)The surface of DCNTs was efficiently coated with CoNi-LDH nanosheets by use of solvothermal method to fabricate DCNTs@CoNi-LDH composite structure.Through the optimization of the solvothermal time and cooling mode,the DCNTs@CoNi-LDH nanoflower core shell hierarchical structure exhibited large specific capacitance(1260 F/g at 1 A/g current density),excellent rate performance(145.2 F/g at 10 A/g current density)and cycle stability(83.1%capacitance retention rate after 5000 cycles at 10 A/g current density).The role of CNTs in the composite structure is further studied by setting DC@CoNi-LDH(free CNTs)as a control electrode,revealing that the improvement of energy storage performance is mainly attributed to the interspersion of CNTs between the LDH overlayers,which provides a rapid electronic transport channel for the energy storage reaction on the surface of LDH.