Preparation Of Co₃O₄ And Its Composites And Their Applications In Supercapacitors

In recent years,with the gradual depletion of traditional fossil energy and the increasing pollution of the ecological environment,there is an increasingly urgent need to seek a new technology for efficient,clean and sustainable development of energy and energy storage and conversion.Supercapacitors have the advantages of long life,high power density,fast charging and discharging,and more importantly,they can reduce environmental pollution and resource shortages.Therefore,it is considered to be a new type of energy storage equipment that is most promising to realize energy efficient storage and conversion.Electrode material is a key factor restricting the energy storage of capacitor devices.Therefore,the development of high-performance electrode materials has become the focus of the current research field of supercapacitor devices.Cobalt tetroxide(Co₃O₄)has attracted wide attention because of its environmental friendliness,easy preparation,and high theoretical specific capacitance.However,the poor conductivity and insufficient ion diffusion of Co₃O₄ have caused its actual specific capacitance to be far lower than the theoretical value.Therefore,improving the electrochemical performance of Co₃O₄ has important practical significance.In this paper,cobalt nitrate is used as the cobalt source,and by adjusting the amount of urea added by the hydrothermal method,without adding any binder,Co₃O₄ with different morphologies is directly grown on the foamed nickel substrate.Their electrochemical performance has been systematically studied.In order to further improve the electrochemical performance of Co₃O₄,the chrysanthemum-like Co₃O₄ was subjected to secondary hydrothermal vulcanization to obtain the Co₃O₄@Co₉S₈ nanorod composite material with a core-shell structure.The main research contents are as follows:(1)Using cobalt nitrate as the cobalt source and water as the solvent,by adjusting the amount of urea,three different morphologies of Co₃O₄ electrode materials with band-like,chrysanthemum-like,and feather-like were synthesized on the foamed nickel substrate.Among them,the chrysanthemum-like Co₃O₄ exhibits excellent electrochemical performance due to its unique three-dimensional structure.When the current density is 1 A/g,the specific capacity can reach 440.1 C/g(880.2 F/g),when the current density is increased to 20 A/g,the capacity retention rate is 70%,and it has excellent cycle stability(After 3000 cycles,the capacity retention rate is 100%),the chrysanthemum-like Co₃O₄ and activated carbon electrode are assembled into an asymmetric supercapacitor device,and the output energy density can reach35.3 Wh/Kg(power density is 788.8 W/Kg),after 10,000 GCD cycles,the capacity retention rate is 82.6%.(2)Choosing chrysanthemum-like Co₃O₄ to vulcanize it under hydrothermal conditions,the nanorod composite Co₃O₄@Co₉S₈ with a core-shell structure was successfully prepared.Transmission electron microscopy(TEM)test results show that the chrysanthemum-like Co₃O₄is partially vulcanized to form Co₉S₈ nanosheets,which are evenly coated on the outside of the chrysanthemum-like Co₃O₄.This core-shell structure can greatly shorten the ion diffusion path and improve the material Electrochemical performance.When the current density is 1 A/g,the specific capacity of Co₃O₄@Co₉S₈ is 1545.1 C/g(3090.2 F/g),which is significantly improved compared with chrysanthemum-shaped Co₃O₄(440.1 C/g(880.2 F/g))and hydrothermally synthesized Co₉S₈(460.6 C/g(921.2 F/g)).The Co₃O₄@Co₉S₈ composite and activated carbon electrode are assembled into a device Co₃O₄@Co₉S₈//AC.After 10,000 cycles of GCD,the specific capacity of the device only loses 7.5%,which is much higher than the chrysanthemum-shaped Co₃O₄ and activated carbon electrode assembly.In addition,the Co₃O₄@Co₉S₈//AC device can continuously illuminate five different colors of LED lights,showing a higher potential application value.