Construction Of Cobalt/Nickel Based Electrode Material Derived From ZIF-67 And Their Applications In Supercapacitors

The energy shortage in the world is becoming increasingly serious.The design and construction of efficient energy storage devices have become an important strategic demand for the sustainable development of today’s society.Supercapacitors,also known as electrochemical capacitor,are a new type of energy storage device,considering to be the next generation with the most development potential of energy storage device due to theirs high power density,long cycle life and rapid charge-discharge,which has great application value in the fields of electric vehicles,hybrid vehicles and aircraft.Currently,supercapacitors exhibit many performance advantages,but their energy density still needs to be improved to facilitate commercial applications.Electrode material is one of the most important components of supercapacitors,further it is also a decisive factor for the electrochemical performance of supercapacitors.Therefore,designing and constructing reasonable electrode materials is one of the effective ways to improve the energy density of supercapacitors.Transition metal compounds are a kind of electrode materials with high theoretical capacitance for supercapacitors.However,transition metal compounds exhibit small specific surface area and poor stability,which can not achieve high capacitance in practical applications.Metal organic framework materials（MOFs）and their derivatives are porous crystal materials,and show large specific surface area,high porosity and stable structural characteristics,which has attracted much attention as electrode materials for supercapacitors.Combining the characteristics of transition metal compounds and MOFs to design and construct a reasonable electrode material structure is one of the effective methods to realize high energy density of supercapacitors.Therefore,a series of composite electrode materials based on ZIF-67 were constructed,and were used as positive electrode of supercapacitors to explore its electrochemical performance.The main contents are as follows:1.The honeycomb nanosheet composite electrode material Co₂P/Ni₂P/Ni Co₂O₄-CC was constructed on carbon cloth（CC）as the matrix through the process of in-situ growth,etching and ion exchange,carbonization and low-temperature phosphatization.Co₂P/Ni₂P/Ni Co₂O₄-CC shows large specific surface area,abundant active sites and high conductivity.Based on this structural feature,Co₂P/Ni₂P/Ni Co₂O₄-CC delivers an outstanding areal capacitance of 2.88 F cm^-2at 2 m A cm^-2 in a three-electrode system.In a two-electrode system,Co₂P/Ni₂P/Ni Co₂O₄-CC//AC-CC exhibits a maximum volumetric energy density of 2.53 m Wh cm^-3at a volumetric power density of 22.77 m W cm^-3,and excellent cycling stability（87.60%after 10000 cycles）.Therefore,the Co₂P/Ni₂P/Ni Co₂O₄-CC derived from MOFs can be regarded as an ideal electrode material for supercapacitors.2.The hierarchical core-shell spiny globe with flat leaves-shaped heterostructure（Co₂P@Ni₂P/Ni Co₂O₄@Co O,CNNCC-NF）was constructed on nickel foam（NF）as the matrix through the process of hydrothermal,coordination,carbonization,etching,and low-temperature phosphatization.The asymmetric supercapacitor device（CNNCC-NF//AC-NF）with CNNCC-NF as a positive electrode,and activated carbon-NF（AC-NF）acted as a negative electrode was assembled,which showed the state-of-the-art performance among the similar supercapacitors.Density functional calculation results confirm that CNNCC-NF shows high conductivity,which ensures high electrochemical reaction activity and rapid reaction kinetics.The core-shell spiny globe with flat leaves-shaped exhibits large specific surface area and excellent pore structure,which provides a good channel for electron transport and ion diffusion.The internal electric fields established in the phase interfaces of Co₂P,Ni₂P,Ni Co₂O₄,and Co O can further improve the conductivity of electronic/ionic and redox reaction kinetics.CNNCC-NF delivers an ultrahigh areal capacitance of 10.11 F cm^-2 at a current density of 2 m A cm^-2(2641.15 F g^-1 at 0.52 A g^-1)in a three-electrode system.Meanwhile,the CNNCC-NF//AC-NF exhibits a high-energy-density of 84.03 Wh kg^-1 at a power density of 364.4 W kg^-1,as well as outstanding durability of 87.30%after 10000 cycles and coulomb efficiency of 95.12%at 20 m A cm^-2(4.40 A g^-1).3.The core-shell rod-shaped radial cluster with hollow structure Co₉S₈@Co O-NF was constructed on NF as the matrix through the process of hydrothermal,carbonization,coordination,and sulfuration,and was used as a positive electrode of supercapacitors.The core-shell rod-shaped radial cluster with hollow structure exhibits large specific surface area and excellent pore structure,which is conducive to active site exposure and ion diffusion.The core-shell heterostructure Co₉S₈@Co O-NF significantly improves the electron/ion conductivity and redox reaction kinetics.The radial cluster structure improves the stability of electrode materials and provides a guiding path for electron transport and ion diffusion.Based on structural and compositional characteristics,Co₉S₈@Co O-NF shows an ultrahigh areal capacitance of 18.13 F cm^-2 at a current density of 3 m A cm^-2.The asymmetric supercapacitor device（Co₉S₈@Co O-NF//AC-NF）with Co₉S₈@Co O-NF as a positive electrode,and AC-NF as a negative electrode was assembled.Co₉S₈@Co O-NF//AC-NF exhibites a high-energy-density of 94.28 Wh kg^-1 at a power density,as well as excellent durability of 93.55%after 10000 cycles and coulomb efficiency of 95.76%at 10 m A cm^-2.The core-shell rod-shaped radial cluster with hollow structure provides a new idea for the design and construction of asymmetric supercapacitor electrode materials.