Synthesis Of ZIF-Derived CoMo Sulfide And Their Electrochemical Properties

Electrochemical capacitors,also known as supercapacitors,are a kind of green and efficient new energy storage devices.Its working principle is to store energy through ion adsorption or surface/interface redox reactions rapidly.The key to the efficacious energy storage of supercapacitors is the rational design of electrode materials.It is very important to develop low-cost and high-performance electrode materials.Zeolite imidazolate framework material(ZIF)is a subclass of metal organic framework material(MOF).Similar to MOF,ZIF has a large specific surface area,rich active sites and high porosity.In addition,when functional nanomaterials are synthesized using ZIF as a sacrificial template,the original morphology and porous structure of ZIF can be effectively retained,which can effectively improve the electrochemical energy storage performance.Therefore,ZIF is widely used as a sacrificial template and precursor to synthesize nanoporous functional materials.In this paper,we mainly study the synthesis of bimetal sulfide electrode materials based on ZIF-67 polyhedron and 2D ZIF-L nanosheet arrays as sacrificial templates and precursor,they are applied in electrochemical supercapacitors.The main research contents are as follows:(1)ZIF-67 with 3D polyhedron structure was obtained by the coordination reaction of Co²⁺and 2-methylimidazole.Mo-doped CoS hollow nanocage(Mo-doped CoS HNC)with hollow porous structure and retained ZIF-67 original morphology was prepared by solvothermal method.For comparison,ZIF-67 was directly vulcanized to obtain CoS HNC.The samples were evaluated in a three-electrode supercapacitor.The test results show that the specific capacitance of Mo-doped CoS HNC reaches 781.0 F g^-1 at a current density of 0.5 A g^-1,which is much higher than the specific capacitance of CoS HNC at the same current density.This indicates that there is synergetic effect between the bimetals.At the same time,Mo-doped CoS HNC and activated carbon(AC)were assembled into an asymmetric supercapacitor(ASC).When the power density is 799.9 W kg^-1,the energy density is as high as 27.7 W h kg^-1,and the initial capacitance is maintained about 88.0%after 10,000 cycles of tests,which indicates that the assembled ASC has good electrochemical performance and excellent cycle stability.(2)2D ZIF-L nanosheet arrays were synthesized by growing Co²⁺and2-methylimidazole on conductive nickel foam through a coordination reaction.After that,the Co₃S₄@MoS₂ core-shell nanosheet array material was successfully prepared using ZIF-L as a template through one-pot of hydrothermal synthesis.When used as a high-performance electrode for supercapacitors,it exhibits excellent electrochemical performance.At 0.5 A g^-1,the the Co₃S₄@MoS₂ delivers a specific capacitance of 1217.5F g^-1,which is higher than that of Co₃S₄/NF and MoS₂/NF at the same current density.In addition,when assembled with an AC electrode into an ASC,it exhibited an extremely high energy density(55.4 W h kg^-1)and excellent cycle stability(87.8%).In summary,this work focuses on using ZIF as a sacrificial template to successfully prepare bimetal sulfide nanomaterials as high-performance electrodes for supercapacitors.The obtained bimetal sulfide exhibits excellent electrochemical performance,and the synergistic effect between the bimetals greatly improves the electrochemical performance of the material.