Electrochemical Properties Of Transition Metal Selenides Derived From Metal-organic Framework As Templates

The multi-modular and highly adjustable structure of Metal Organic Frameworks（MOFs）adds more active sites for electrochemical reactions.However,the low capacity,poor conductivity and unstable structure of MOFs greatly limit their direct use as electrode materials.Therefore,MOFs are often used as self-sacrificial templates to derive unique structures,and further modification measures are taken to build heterogeneous interface composites to improve their electrochemical performance.Moreover,the chemical bond between selenium atom and bonding electron is weak,and transition metal selenides（TMSe）show higher electrochemical activity.In this paper,ZIF-8 with orthododecahedral structure was selected as a self-sacrificing template to investigate the effect of transition metal selenide heterogeneous interfacial composites derived with graphene oxide（r GO）,Co-based compounds of different morphologies on the electrochemical properties.The main research contents are as follows:（1）ZIF-8 derived Zn Se@r GO nanocomposites were prepared by electrostatic self-assembly to enhance the electrochemical performance of supercapacitors.The ZIF-8@r GO precursors with orthododecahedral skeleton structure were obtained by homogeneous growth of ZIF-8 on r GO,and the Zn Se@r GO nanocomposites with three-dimensional skeleton structure were subsequently prepared by chemical vapor phase reaction.Its unique structure effectively alleviates the self stacking phenomenon of graphene,which not only improves the conductivity of electrode materials,but also enhances the structural stability,significantly improving the electrochemical performance.（2）Hollow nanobox-like Co Se₂@Zn Se/r GO composite electrode materials derived by graphene-stabilized growth of double MOFs were used to enhance electrochemical performance.Benefiting from the large specific surface area of r GO,the excellent electrical conductivity of transition metal selenides and the hollow nanobox-like skeleton structure that effectively slows down the volume expansion during the reaction,the composites exhibit excellent electrochemical properties.The Co Se₂@Zn Se/r GO electrode has a specific capacitance of 2075.4 F g^–1at a current density of 1 A g^–1and a capacitance retention of83.0%after 3000 consecutive charge/discharge cycles.The hybrid supercapacitor assembled based on Co Se₂@Zn Se/r GO cathode and activated carbon（AC）cathode has an energy density of 85.3 Wh kg^–1at a power density of 1279.9 W kg^–1.（3）A ZIF-8-derived selenium-doped needle-like nanosphere Se-Co Se₂@Zn Se heterostructure was designed.The specific capacitance of Se-Co Se₂@Zn Se-5 at 1 A g^–1is2469.1 F g^–1and the capacitance retention after 3000 cycles is 85.3%.The assembled asymmetric supercapacitor provides an energy density of 68.8 Wh kg^–1at a power density of1280.0 W kg^–1.The excellent electrochemical performance is attributed to the selenium doping increasing the active sites in the reaction process,the construction of heterogeneous interfaces enhancing the synergy between Zn and Co ions,the generation of internal electric fields,the optimization of electron distribution and the special structure effectively increasing the porosity and specific surface area.In addition,Density Functional Theory（DFT）calculations indicate that Se-Co Se₂@Zn Se-5 has a higher Density of State（DOS）near the Fermi level.