Synthesis And Electrochemical Performance Of MOFs-derived Transition Metal Sulfide Composites For Supercapacitor

Supercapacitors(SCs)have received extensive attention in recent years because of their unique properties such as high power density,high charge-discharge rate and long-cycle stability.To prepare high-performance supercapacitors,the high conductivity,high thermal stability and large specific surface area of the electrode materials are crucial.Compared with metal oxides,transition metal sulfides have high electrical conductivity,mechanical and thermal stability and other unique chemical and physical properties,which have become an important class of electrode materials for SCs.In addition,metal sulfides also have rich redox chemical properties that help increase the specific capacity.Metal-organic frameworks(MOFs)have the advantages of high porosity,large specific surface area,adjustable structure,etc.,and have received extensive attention in energy storage materials.However,due to the poor conductivity of MOFs,only a very small number of synthesized MOFs can be directly used as energy storage materials,which restricts the development of MOFs in energy storage materials.In recent years,the use of MOFs as precursors to prepare metal sulfides and their composites as energy storage materials has attracted wide attention from researchers.This thesis mainly uses classic MOFs materials and MOFs composite materials with mature synthesis routes as precursors.By controlling the temperature of vulcanization and calcination,and reasonably controlling the composition and structure of derivative materials,MOFs-derived nanomaterials derivative nano-materials are obtained.The in-depth study of material electrochemistry has laid the foundation for its application in solving energy and environmental problems.The specific research content and results are as follows:1)By using the designed Co_0.8Fe_0.2-MOF-74@rGO as the precursor,sulfided and calcined in the range of 780-830?to obtain transition metal oxides with high redox activity and transition metal sulfides with strong conductivity composite material Co_1-xS/CoFe₂O₄@rGO.The electrochemical test results show that the composite material has excellent electrochemical performance.When the current density is 1 A g^-1,the specific capacity is as high as 2202 F g^-1,and the composite material exhibits significant cycle stability(20,000cycles)After it can still maintain more than 90%of the original),Co_1-xS/CoFe₂O₄@rGO is assembled into an asymmetric supercapacitor,which shows an energy density of up to 61.5Wh kg^-1 at a power density of 700 W kg^-1.The combination of experimental results and Density Functional Theory calculations(DFT)shows that the excellent electrochemical performance of the material is due to the Co_1-xS/CoFe₂O₄ interface with optimized electronic structure,which promotes the electron transfer pathway and realizes the high CoFe₂O₄effective synergy of redox activity and good conductivity of Co_1-xS.2)Based on the slightly different thermodynamic stability between ZIF-67 and Co Ni-LDHs,a ZIF-8@Co Ni LDHs precursor with a core-shell structure was synthesized through a simple method,and the vulcanization and calcination temperature of the precursor was controlled to 450?,the core-shell structure of Zn S@Zn_0.76Co_0.24S/Ni S-NC was obtained.The electrochemical test results show that the specific capacity reaches 1931 F g^-1 at 1 A g^-1,which is a significant increase compared to the precursor.In addition,the asymmetric supercapacitor assembled with Zn S@Zn_0.76Co_0.24S/Ni S-NC as the anode and activated carbon as the cathode shows 65.6 Wh kg^-1 at a power density of 700 W kg^-1 High energy density,and still has excellent cycle performance after 3000 cycles.The excellent electrochemical performance can be attributed to the core-shell structure which increases the stability of the material and provides a fast channel for ion/electrolyte transfer.At the same time,the synergistic effect of metal sulfide and composite materials can also increase the specific capacity.