Structural Regulation And Electrochemical Properties Of Binary Metal Oxides And Sulfides

In recent years,supercapacitors have been considered as one of the devices with the characteristics of excellent energy storage equipment.Because of its advantages such as high power and long cycle life,which provides important value for solving worldwide energy storage problems.As a kind of important electrode materials,binary metal oxides and sulfides have been widely used in supercapacitors.Because of their high theoretical specific capacity,they have been proved to be one of the promising electrochemical active materials.However,the reported binary metal oxide and sulfide electrode materials limit their wide application due to poor chemical stability and low coulombic efficiency.To solve this problem,the structures of binary metal oxide and sulfide materials are regulated to optimize the electrochemical performance of the electrode from the preparation of special morphology,the control of oxygen defects and the design of heterostructure in this paper.And the hybrid supercapacitor was assembled to evaluate its performance.The specific work is as follows:（1）NiCo₂O₄ supercapacitor electrode materials with unique one-dimensional（1D）and two-dimensional（2D）hybrid nanostructures were prepared on nickel foam（NF）by a simple hydrothermal method.Due to its unique structure,Ni Co₂O₄ has more active sites and porosity,leading to its improved electrochemical performance.The optimized Ni Co₂O₄ electrode has a low charge transfer resistance（0.32Ω）and a specific capacity as high as 450 F·g^-1at a specific current of 0.5 A·g^-1,and a cycle stability of 139.6%.The improved electrochemical energy storage performance of Ni Co₂O₄ demonstrates the potential application of binary metal oxides in the field of electrochemical energy storage.（2）The defective NiCo₂O₄ nanosheets（V-Ni Co₂O₄-4）were prepared by solvothermal and chemical reduction methods.The prepared nanosheets with oxygen vacancies have large surface area and abundant active sites.After performing density functional theory（DFT）calculations,it was found that more electrons can transition from the valence band to the conduction band,giving it excellent electrical conductivity.At a specific current of 1 A·g^-1,the specific capacity of the electrode is 751.7 m Ah·g^-1,and the assembled supercapacitor can achieve a specific energy of 57.1 Wh·kg^-1 at a specific power of 241.5 W·kg^-1.The capacity retention rate after 10000 cycles is 91.9%.This work lays the foundation for fine-tuning the electronic configuration and reaction kinetics.（3）The petal-like of high specific capacity composite Co₃O₄@Co Ni₂S₄ core-shell heterostructures derived from metal-organic frameworks（MOFs）were prepared by solvent method and electrodeposition.MOFs-derived metal oxides act as frameworks with large specific surface area of pores,which are beneficial for interfacial transport and electrolyte diffusion.Meanwhile,the synergistic effect of the unique core-shell structure can significantly enhance the electrochemical performance of the composite materials.At a specific current of 1 A·g^-1,it has a specific capacity of 244.4 m Ah·g^-1and a rate capability of 81.3%at a current density of 16 A·g^-1.In addition,the assembled Co₃O₄@Co Ni₂S₄//AC supercapacitor achievs a specific energy of 55.6 Wh·kg^-1 at a specific power of 884.4 W·kg^-1,and the capacity retention rate is 86%after 10000charge-discharge cycles,confirming that this work opens up a new avenue for the fabrication of high-performance supercapacitor electrodes.