Preparation And Electrochemical Properties Of Cu,ni And Co Based Transition Metal Compound Electrode Materials

With the urgent demand for large capacity energy storage devices,the design and fabrication of new electrode materials have become a research hotspot in the fields of new energy and materials science.Compared with lithium-ion batteries,supercapacitors（SCs）have the characteristics of rapid charging and discharging,high power density,and a high factor of safety.The type of electrode materials determines the electrochemical performance of supercapacitors.Therefore,it is important to develop electrode materials with high capacitance,good rate capability,and good durability.Transition metal compounds（TMCs）and their composites have been extensively studied for SCs.The main idea of this paper is to improve the comprehensive performance of supercapacitors by using the synergistic effect of multi-component materials through the design of electrode structure and the control of morphology,size and interface of Cu,Ni and Co-based transition metal compounds,combined with characterization methods such as phase and microstructure.We explored the mechanism of microstructure evolution,morphology,and elemental valency.The mechanism of energy conversion and storage was revealed by the corresponding electrochemical test methods.The specific research contents are as follows:（1）A novel MOF-to-LDH strategy was used to generate Cu-BDC@Ni Co-LDH with 3D core-shell structure on the surface of copper foam by anodic oxidation and two-step solvothermal methods.Active materials are stably integrated on a conductive substrate,the Ni Co-LDH shell plays a role in protecting a layer and providing redox active sites,and the Cu-BDC framework enhances the structural stability.In the electrochemical test,an ultrahigh specific capacitance of 2674 F g^-1(Current density of4 m A cm^-2,area specific capacitance of 11.2 F cm^-2)was provided at a current density of 1 A g^-1,and a good cycle performance（84.92%retention after 5 000 cycles）was achieved.The CF@Cu-BDC@Ni Co-LDH//AC asymmetric supercapacitor（ASC）was fabricated,and the highest energy density was 59.56 Wh kg^-1 at the power density of800.06 W kg^-1.It has a maximum power density of 6397.97 Wh kg^-1 and shows good cycling stability（Capacitance retention of 89.4%after 6000 cycles）.In the test of electrocatalytic OER,CF@Cu-BDC@Ni Co-LDH electrode can obtain a low overpotential of 306 m V and a small Tafel slope of 34.2 m V dec^-1 at the current density of 100 m A cm^-2,which can show excellent electrocatalytic performance and excellent electrochemical stability for OER.（2）Core-shell arrays of CF@Cu₃P@Ni Co-P were prepared by a combination of anodization,solvothermal and vapor deposition methods.The three-dimensional micro-hierarchical structure provides a large surface area to increase the exposure of active sites.In the three-electrode system,when the current density is 2 m A cm^-2 and the scan rate,the area specific capacitance reaches 11.64 F cm^-2,and even if the current density is increased by ten times,the area specific capacitance is still maintained at 7.13 F cm^-2,showing good rate capability.The capacity loss is only 6.6%after 5000 charge-discharge cycles.The assembled CF@Cu₃P@Ni Co-P//AC-ASC device has a maximum power density of 7,250.63 W kg^-1 at an energy density of 25.78 Wh kg^-1,indicating excellent energy storage performance of ASC.After 6000 cycles,the CF@Cu₃P@Ni Co-P//AC-ASC device showed remarkable cycling stability with a high-capacity retention of94.35%.（3）Through electroless copper plating on carbon cloth with flexible substrate,the combination of Cu₂₊₁O@Ni Co-S active material and flexible substrate was realized by anodic oxidation and solvothermal reaction,and the double-layer trimetallic heterojunction with nano-scale structure was prepared.The perfect combination of the transition metal and the carbon material is realized,and the problem that the active material is easy to peel off from the flexible substrate in the electrochemical reaction is effectively solved.The vertically aligned CCPC@Cu₂₊₁O@Ni Co-S electrode has highly open channels,allowing rapid electrolyte diffusion into the electrode,resulting in excellent cycling stability,ultra-high specific capacity,and high conductivity.In the three-electrode system test,an ultrahigh specific capacitance of 10.41 F cm^-2 was supplied when the current density was 2 m A cm^-2,and the rate of retention of the capacitance was 71.1%when current density was increased by a factor of ten.It has excellent cycle performance（91.1%retention after 10000 cycles）,and the coulombic efficiency is close to 100%.A CPCC@Cu₂₊₁O@Ni Co-S//AC flexible asymmetric supercapacitor was prepared,which achieved a high energy density of 50.82 Wh kg^-1 at a power density of 802.8 W kg^-1,and maintained a maximum power density of 8 000W kg^-1 at an energy density of 20 Wh kg^-1.The capacitance retention was 94.71%after10000 cycles at a high current density of 15 A g^-1,showing excellent cycle stability.