Study On Preparation And Electrochemical Performance Of MOFs Derived Cobalt-Nickel Compound And Its Composites

As a research hotspot of energy storage device,supercapacitors have the characteristics of fast charge-discharge process,long cycle life and high power density.Among the components of supercapacitors,electrode materials are the important factor for achieving charge storage and affecting electrochemical performance,and are usually served by materials with large specific surface area and porous structure.Metal organic framework materials?MOFs?,as a kind of porous crystal material with controllable structure,good thermal stability and high specific surface area,have attracted more and more attention in the application field of supercapacitors in recent years.However,due to its poor conductivity,it will reduce the cycling stability of supercapacitors if MOFs are used directly as electrode materials.Therefore,using MOFs as a sacrificial template to prepare high-performance metal compounds is the preferred choice to solve the defects faced by in supercapacitors electrode materials.In this paper,porous nickel-cobalt electrode materials with high specific capacitance were prepared through simple and efficient methods based on MOFs.In order to improve the cycle stability of Nickel-Cobalt hydroxides,the method of in-situ growth strategy and compositing with high conductivity materials were applied to enhance the structural stability and electrical conductivity.The main work of this study is as follows:?1?Taking ZIF-67 as the research object to explore its morphology control method.Hexadecyl trimethyl ammonium Bromide?CTAB?was selected as the modifier to obtain various morphologies of ZIF-67 by adjusting the corresponding mass fraction in the solution.In the hydrothermal environment with deionized water as the solvent,when the mass fraction of CTAB was 0 wt%,0.16 wt%,0.24 wt%and 0.35 wt%,the ZIF-67 crystal particles will transform into the shape of rhombic-dodecahedron,octagonal plates and nanorod.Also,the formation mechanism of different morphologies of ZIF-67 were discussed.?2?Choosing rhombic-dodecahedron-shaped ZIF-67 as the sacrificial template and cobalt source,thioacetamide?TAA?as the sulfur source,the hollow Co S nanocages were obtained after being kept in the ethanol solvent at 90?for 1 hour by reflux heating method.Another group took Ni?NO₃?₂ as the nickel source to etch Co S under the same reaction condition and obtained hollow Co Ni₂S₄ nanocages covered with crossing nanosheets.It was found that the specific capacitance of Co S and Co Ni₂S₄were 414 F/g and 2255.8 F/g at the current density of 1 A/g by testing the electrochemical properties.Co S and Co Ni₂S₄have the specific retention remained at57.4%and 70%after 1000 cycles respectively at 3 A/g.?3?A facile and green solvent synthesis method was employed to prepare hollow NiCo-LDH nanoflakes grown in situ on nickel foams at room temperature.By preparing Co-MOFs as the precursor in deionized water and then adjusting the Ni²⁺ion exchange reaction time,the surface morphology and electrochemical performance of NiCo-LDH electrode materials could be greatly optimized.NiCo-LDH nanoflakes with a thickness of 150 nm as electrode material had a high specific capacity of 2148 F/g at the current density of 1 A/g,and possessed the cycling stability of 82%capacity retention after 1000 cycles.?4?In order to further improve the conductivity of NiCo-LDH,NCLDH/CNTs composite materials were prepared with carbon nanotubes?CNTs?as the doped phase.Using rhombic-dodecahedron-shaped ZIF-67 as a sacrificial template,ZIF-67@CNTs composites with optimal morphology can be obtained by changing the composite mass ratio of CNTs at room temperature.Then Ni?NO₃?₂ was added and kept together at 120?for 6 hours under hydrothermal conditions.Finally,the hollow nanocage shaped NCLDH@CNTs composites with uniform cross-growth of NCLDH and CNTs was prepared and covered with ultrathin nanosheet structures.The specific capacitance of NCLDH@CNTs was 2300 A/g at 1 A/g and the cycling stability maintained 85%of the initial specific capacitance at the current density of 5 A/g.