Design And Synthesis Of MOF-guided Nano-electrode Materials And Their Energy Storage Performances

Supercapacitor is an energy device,which stores energy by means of generating polarized electrolytes.It not only inherits the advantages of fast charging and discharging and long service life of traditional capacitors,but also has the ability of secondary charging and discharging capability of batteries.To improve the energy storage capability of superpacitor,it is imperative to design and synthesis of high-performance electrode materials.Metal-organic framework(MOF)refers to the three-dimensional network structure formed by the coordination of transition metal ions and ligands in a suitable solvent.MOF has the advantages of good crystallinity,large specific surface area,high porosity,structural diversity,and adjustable pore size.These advantages can be used to design a suitable material for supercapacitor.MOF-derived materials can keep the porous structure and unique morphology of pristine MOF,which is conducive to the improvement of electrochemical performance.Therefore,MOF has been widely explored as an ideal self-sacrifice template or precursor.In this study,we focus on the supercapacitor performance of MOF-guided 3D hierarchical core-shell nanostructured metal sulfide/oxide arrays,and their potentials in practical applications.The main contents are as follows:1.Using nickel foam as a conductive substrate,through the coordination of Co²⁺and 2-methylimidazole,a leaf-shaped Co-ZIF-L nanosheet array was in situ grown on;and it was sulfurized to form Co₃S₄nanosheets by a simple hydrothermal reaction.After that,a layer of Co(OH)₂sheet was wrapped on the skeleton of the Co₃S₄nanosheet to obtain a Co₃S₄@Co(OH)₂core-shell nanosheet array.The electrochemical property of Co₃S₄@Co(OH)₂nanosheet array electrode was tested in 1 mol L^-1KOH electrolyte.The Co₃S₄@Co(OH)₂shows a specific capacitance of 2974 F g^-1at a current density of 1 Ag^-1,and still keep 76%of the capacitance after at 10 Ag^-1.The Co₃S₄@Co(OH)₂was assembled with activated carbon(AC)as the negative electrode material to form an asymmetric supercapacitor(ASC).When the power density is 1125.9W kg^-1,the energy density reaches up to 41.0 Wh kg^-1.In addition,two ASCs in series successfully lit an LED light for more than 3 minutes,proving that the electrode has great practical application value.2.On the basis of the MOF-guided strategy,Co₃O₄nanosheet arrays were obtained bycalcining Co-MOF-L in air,and then through a hydrothermal syntheis and a post-annealing in air,a uniform layer of Ni Co₂O₄nanoflakes was grown on the original sheet to obtain Co₃O₄@Ni Co₂O₄,nanosheets.The obtained Co₃O₄@Ni Co₂O₄,as a battery material,exhibits a specific capacity up to544.2 C g^-1at the current density of 1Ag^-1with excellent cycle stability.The ASC assembled with Co₃O₄@Ni Co₂O₄as the positive electrode material and AC as the negative electrode can deliver an energy density as high as 36 Wh kg^-1when the power density is 852 W kg^-1.At the same time,the ASC demonstrates an excellent electrochemical cycle stability.After 10000 cycles at 10Ag^-1,it has a capacitance retention rate of 89.5%and a coulomb efficiency of 95.2%.In addition,two ASCs in series also successfully light up an LED.In conclusion,this study has successfully synthesized core-shell nanosheet array electrode materials on conductive nickel foam using leaf-like Co-MOF-L nanosheet arrays as precursors and templates,and their morphology,composition,and supercapacitive performance were studied in depth.The result suggests that the core-shell nanosheet array has great potential in practical applications.At the same time,the MOF-guided strategy of synthesis of core-shell structured materials provides a more practical method for preparing more efficient and clean electrode materials.