Preparation And Performance Study Of Flexible Electrode Materials Based On Carbon/MOFs Derivatives For Supercapacitor

The rapid rise of the new energy industry and the rapid development of various electronic devices have expanded the market demand in the field of energy storage.Among many energy storage devices（fuel cells,lithium-ion batteries,supercapacitors,etc.）,supercapacitors have the advantages of short charge process,high cycle stability and environmental protection,which is in line with the inevitable trend of the development of energy storage devices.As a result,the overall scale of its industry market is growing.However,the reality is that the low energy density is a disadvantage that limits the application of supercapacitors in some fields.Supercapacitors mainly rely on redox reactions and ion absorption occurring on the electrode surface for energy storage.Therefore,the preparation of high performance electrodes is very important to improve the energy density of supercapacitors.Metal-organic framework（MOFs）materials have unique structural advantages such as large surface area,abundant active sites and excellent porosity.It is always used as precursors to prepare corresponding MOFs derivatives.The MOFs derivatives not only retain the original structural advantages of MOFs,but also have surface hydrophilicity,which is conducive to ion diffusion and adsorption.It is recognized as a energy storage device materials with great development potential.However,the poor conductivity and stability of most MOFs derivatives prevents them from achieving the desired excellent performance.Carbon materials（such as graphene and carbon nanotubes）are widely used as conductive substrates.Their excellent electrical conductivity,excellent stability and mechanical flexibility provide feasible solutions for the design of flexible electrode materials.The main idea of this paper is to prepare flexible self-supported thin film electrodes with high capacity and long cycle life by combining MOFs derivatives with carbon materials.The main research contents and results are as follows:（1）The flexible conductive substrates（GO/CNTs）of GO and carbon nanotubes were prepared by vacuum filtration.Then,Co Zn-MOF nanosheets were grown on both sides of the substrate,and after Ni²⁺exchange,annealing and phosphating,Co Zn Ni OP@r GO/CNTs（CZNP@GC）composite films were finally obtained.After phosphating,the redox activity of the material was enhanced,the r GO and CNTs could improve the electrical conductivity of the whole material.The specific capacity of the electrode is 1416.5 F g^-1at 1 A g^-1.An asymmetric supercapacitor is assembled with CZNP@GC as the positive electrode and C@r GO/CNTs（C@GC）as the negative electrode.The energy density of the device can reach 59.9 Wh kg^-1(power density at800 W kg^-1).After 6000 cycles,the capacitance retention rate of supercapacitor is85.6%.（2）In order to further improve the electrochemical performance of the composite films,we still used GO/CNTs as the conductive substrate,Co Zn-MOF nanosheets were grown on the surface of Ni Co₂O₄@r GO/CNTs.The Ni Co₂O₄/Zn Co₂O₄@r GO/CNTs（NZ@GC）composite films were prepared by annealing.The unique structural design and abundant active sites improve the stability of materials and the utilization of active substances.According to the test results,the optimal specific capacitance of NZ@GC can reach 1128.6 F g^-1.The hybrid supercapacitor with NZ@GC as the positive electrode and activated carbon（AC）as the negative electrode exhibits the specific energy density of 50.8 Wh kg^-1.After 9000cycles at the current density of 10 A g^-1,the capacity of supercapacitor still retains86.1%of the initial capacitance.（3）In order to obtain high-performance flexible electrodes,firstly,the ZIF-67@CNTs film were prepared with CNTs was interspersed in the ZIF-67（Co-MOF）polyhedron structure.Subsequently,CuCo-LDH@CNTs composite materials were obtained by copper ion exchange.Finally,the obtained samples were immersed in black phosphorus quantum dots（BPQD）to obtain CuCo-LDH/BPQD@CNTs flexible self-supporting films loaded with BPQD.The insertion of CNTs improved the electron transport characteristics of the whole material.BPQD has high carrier mobility,which can further improve the electrochemical activity of the material.The CuCo-LDH/BPQD@CNTs electrode can achieve a high specific capacity of 1061.6 F g^-1at 1 A g^-1,and the supercapacitor assembled with BPQD@CNTs as negative electrode exhibits a high specific energy of62.1 Wh kg^-1.After 10000 cycles,79.1%of the original capacity of the supercapacitor is still retained.