Preparation And Electrochemical Energy Storage Of Nickel-cobalt Based Double Metal Oxide Nanoarrays

Electrochemical energy storage has received much attention as an effective way to solve energy crisis and environmental pollution.As a representative electrochemical energy storage system,supercapacitors have been widely studied because of their high power density,excellent rate performance,wide operating temperature range and good cycle stability.However,the practical application of supercapacitors is limited because of its low energy density.The most important factor affecting the performance of supercapacitors is the properties of the electrode materials.Therefore,the development of electrode materials with excellent performance and high energy density has become a hot spot of current research.Transition metal oxides are one of the ideal supercapacitor electrode materials due to their high theoretical specific capacitance,but they also have disadvantages such as poor cycle performance and low rate performance.Constructing reasonable nanostructures and compounding with other materials are two effective ways to improve the properties of materials.In this paper,nickel-cobalt-based metal oxides were selected as research objects and the following work was carried out by constructing a suitable nano-array structure and compounding with graphene to develop a high-performance supercapacitor（1）A simple hydrothermal method was used to construct NiCoO₂ nano-array on the Ni foam by adjusting the time of hydrothermal reaction.This structure can effectively increase the specific surface area and shorten the transport of ions and electrons,thereby increasing the specific capacity of the material and improving the rate performance.Moreover,the electrochemical results show that the sample with 6h hydrothermal time has the best performance,which capacitance reaches 1590.5 F g^-1at 0.5 A g^-1 and still reaches 1175.6 F g^-1at 40 A g^-1 current density.After assembling the material into an asymmetrical device,the energy density reached a maximum of 32.7 Wh kg^-1 at a power density of 0.48 kW kg^-1.（2）A 3D graphene framework was constructed by freeze-drying method,and NiCoO₂ nanosheet@nanowire array with heterostructure were prepared by hydrothermal method.By controlling the hydrothermal reaction time to optimize the heterostructure of the composite material,the advantages of graphene and NiCoO₂ were effectively exerted.The electrochemical test results show that the NiCoO₂@rGO/NF-6h sample with the hydrothermal time of 6h has the best electrochemical performance,and its specific capacitance is up to 1970 F g^-1.After 5000 cycles,it can maintain at 1369 F g^-1.When NiCoO₂@rGO/NF-6h was assembled as an cathode into an asymmetric supercapacitor,the maximum energy density at a power density of 0.4 kW kg^-1 was up to 42.3 Wh kg^-1.（3）The serrated NiCoO₂,nano-array was prepared by simple hydrothermal method.On this basis,an electrodeposition method was used to prepare the hierarchical NiCoO₂@NiCoOO₂ nano-array.This structure can provide more electrochemical active reaction sites because of the more accessible specific surface area,which leads to an increase in material utilization and thus improved electrochemical performance.At the same time,we controlled the electrochemical performance of the composite NiCoO₂@NiCoO₂ by changing the number of NiCo02 electrodeposition times.The test results show that the specific capacitance of the sample deposited by 20 times reached 2059.3 F g^-1 at 0.5 A g^-1.When the NiCoO₂@NiCoO₂ hierarchical structure material was used as the cathode to assemble an asymmetric device,the energy density can reached 44.17 Wh kg^-1 at a power density of 0.48 kw kg^-1.