Studies On Preparation And Supercapacitor Performance Of Electrode Materials Based On Co-MOF

Supercapacitors is a kind of green energy storage device with ultrahigh power density and ultra-long cycle life.Owerver it still suffers from the limitation of low energy density.Therefore,finding an electrode material suitable for supercapacitors has become one of the most important ways to improve its performance.In recent years,metal-organic frameworks（MOFs）with adjustable pore size,stable porous structure and ultra-high specific surface area have been widely used as universal sacrificial templates for supercapacitor electrode materials,especially a special zeolite imidazolate framework structure material（Zeolitic imidazolate frameworks-67,ZIF-67）.This kind of material has the advantages of low cost,simple preparation process,stable structure and environmental friendliness.In this paper we utilized ZIF-67 as precursor,a series of MOFs composites and MOFs derivatives were prepared as supercapacitor electrode materials.Their structures were characterized by X-ray diffraction,infrared spectroscopy,scanning electron microscopy and transmission electron microscopy.The three-electrode system and two-electrode system were applied to characterize their electrochemical performance.The main research contents are as follows:（1）ZIF-67 with good morphology was prepared by precipitation method using Co（NO₃）₂·6H₂O and 2-methylimidazole as raw materials,and utilized as template for the synthesis of porous Co₃O₄.Heterostructure NiCo LDH/Co₃O₄ has fast transport of electrolyte ions and electrons.Electrochemical test results show that the composite（NiCo LDH/50mg Co₃O₄）prepared when the mass ratio of NiCo LDH to Co₃O₄ is 1:50 shows a specific capacitance exceeding 1393.9 F/g at a current density of 1 A/g.And it also has excellent rate performance and ultra-low impedance.In addition,it is assembled with activated carbon to form an asymmetric water-based supercapacitor,which exhibits ultra-long cycle life,ultra-high energy density and high power density.（2）Based on Ni（OH）₂ and Co（NO₃）₂·6H₂O and 2-methylimidazole as raw materials,ZIF-67/Ni（OH）₂ composites with excellent structure were prepared.NiCo LDH/Ni（OH）₂composites with different scale structures which are favorable for electrochemical performance were prepared by a simple ion exchange method.Electrochemical performance tests show that NiCo LDH/Ni（OH）₂-1 has an ultra-high specific capacitance of 2382.9 F/g at a current density of 1 A/g.EIS results show that the material has very low contact resistance and charge transfer resistance.Using it as a positive electrode material to assemble an asymmetric supercapacitor,the device has a specific capacitance loss rate of only 0.6%after1000 cycles at a current density of 5 A/g,and It has a very high energy density of 42 W h/kg at a power density of 720 W/kg.（3）In the process of synthesizing Co-MOF,Zn（NO₃）₂·6H₂O was added to prepare rod-shaped CoZn-MOF.As a precursor,a ZnO/ZnCo₂O₄ composite capable of maintaining a rod-like structure was obtained by heat treatment.The electrochemical results show that the composite prepared at 600°C（CoZn-MOF-600）has an excellent specific capacitance,exhibiting a maximum capacity density of 45 W h/kg.