Design And Synthesis Of Zif-derived Nanostructure Electrode Materials For Energy Storage

Supercapacitor(SCs),as an economical and efficient new energy storage device,has many advantages,such as fast charging and discharging,long cycle life,high power density and so on.However,the low energy density also limits its practical application.Therefore,in order to improve the energy storage performance of supercapacitors,the most important thing is to design suitable electrode materials.Zeolite imidazole skeleton material(Zeolitic imidazolate frameworks,ZIF),is the MOF(Metal-organic Frameworks,MOF)category,is composed of transition metal ions and imidazole ligands of ordered porous functional materia.Besides,it has some advantages of MOF,such as large specific surface area,adjustable pore size,ordered crystal structure,various organic functional groups,rich redox active sites and so on.In addition,ZIF-oriented nano-materials can retain the porous structure and morphology of the original ZIF,which is beneficial to improve the electrochemical energy storage performance.Therefore,it is widely used as an ideal self-sacrifice template or precursor.In this study,we mainly studied the 2D leaf-like ZIF-guided metal sulfide and 3D composite nanoarray structure in the field of supercapacitors.The main contents are as follows:(1)Using the coordination of Co2+ and 2-methylimidazole,2D leaf-like Co-ZIF-L nanoarray was grown on conductive substrate foam nickel in situ;then,the two-dimensional bimetallic zinc-cobalt leaf-like ZIF nanoarray(ZnCo-ZIF-L/NF)was successfully prepared by adding zinc metal and adjusting the ratio of zinc to cobalt for the first time.The two kinds of leaf-like ZIF,were sulfided by solvothermal method,and the 2D leaf-like porous Co9S8/NF and Zn-Co-S/NF nanoarrays were successfully prepared for the first time.Porous Co9S8/NF and Zn-Co-S/NF were tested in 1 M KOH electrolyte by electrochemical method.The results show that the specific capacitance of Co9S8/NF is as high as 1098.8 F g-1 at 0.5 A g-1.The power density of the asymmetric supercapacitor(ASC),assembled with the anode material activated carbon(AC),is 828.5 W kg-1,and the energy density reaches 20.0 Wh kg-1;The specific capacitance of Zn-Co-S/NF was as high as 2354.3 F g-1 at 0.5 A g-1.After 1000 cycles,the capacitance retention rate was 88.6%.Based on this,we have developed a new chemical etching-ion exchange method,and successfully fabricated the Ni-Co-S hierarchical nanoarray.When it is used as electrode material,the specific capacitance reaches 1406.9 F g-1 at 0.5 A g-1,and the capacitance retention rate reaches 88.6%after 1000 cycles.When assembled with AC to form ASC,the energy density is 24.8 Wh kg-1,the maximum power density can reach 8.5 kW kg-1.(2)Using bimetallic ZIF as a self-sacrificing template,we have successfully designed 3D hierarchical ZnCo2O4@Ni(OH)2/NF core-shell arrays.Based on the synergetic effect of ZnCo2O4 as "core",Ni(OH)2 as shell",the core-shell nanoarray as electrode material,the energy storage energy is excellent.At 1 mA cm-2,the specific capacitance is 3063.2 mF cm-2.When assembled with AC,the power density and energy density of ASC,are up to 8.02 kW kg-1 and 40.0 Wh kg-1,respectively.After 5000 cycles at 10 A g-1,the capacitance retention is up to 98.4%,which shows good cycle stability.Besides,the asymmetric supercapacitor device can successfully light up the LED lamp in practical applications.In this thesis,using 2D leaf-like ZIF as template or precursor,mono/bimetallic sulfides or composite electrode materials were successfully prepared on conductive substrate.The effects of different structures and chemical compositions on electrochemical energy storage were also investigated.At the same time,the synthesis method of ZIF and its derivatives is simple and easy to operate,which provides an effective path for the construction of other energy storage materials.