Fabrication And Electrochemical Properties Of Core/Shell Bimetallic Nanoarray

Supercapacitors,also known as electrochemical capacitors.Due to the advantages of high power density,long cycle life and fast charge and discharge,supercapacitors are widely used in instruments,electric vehicles,electronic devices,national defense,military,aerospace and other fields.As electrode materials are the main key factors affecting the performance and production cost of supercapacitors,the research and development of electrode materials for high performance and low cost supercapacitors is an important part of the research and development of supercapacitors.At present,because of the advantages of bimetallic compounds,such as high theoretical specific capacitance,low cost,relatively friendly environment and alkali corrosion resistance,bimetallic compounds have been paid more attention to and studied by researchers,among the electrode materials studied in many fields,such as high theoretical capacitance,low cost,relatively friendly environment,etc.However,bimetallic compounds also have the disadvantages of poor conductivity and low cycle stability.In this paper,a series of bimetallic composites with core-shell structure have been prepared by hydrothermal and other methods.The structure,surface energy and electrochemical properties of the composites have been studied,and the influence mechanism among them has been discussed.The specific contents of the study are as follows:First,a highly ordered NiCo₂S₄ nanosheet was prepared by one step-by-step hydrothermal method on a Ti-substrate grown on a TiO₂ nanobelt to obtain a core/shell array structure?short TiO₂@NiCo₂S₄?of a TiO₂ nanobelt coated with NiCo₂S₄nanosheet,and the method is used as an adhesive-free electrode for a supercapacitor.Three-electrode measurements showed that the specific capacitance of the TiO₂@NiCo₂S₄ electrode was 1300 F g^-1 at 1 A g^-1.When the current density is from1 A g^-1 to 10 A g^-1,the specific capacitance can be kept at 80%,and the specific capacitance can still be maintained at 82%after 5000 charge-discharge cycles at 8 A g^-1,which indicates that the TiO₂@NiCo₂S₄ electrode has a higher specific capacitance.good rate performance,excellent cycle stability.The reasons may be due to the high conductivity of TiO₂,the short ion transport channels in core-shell structure,and the synergistic effect between many reactive sites in NiCo₂S₄ nanosheet.In addition,the coal-based porous carbon?CPC?was used as the negative electrode and the TiO₂@NiCo₂S₄ as the positive electrode to assemble the TiO₂@NiCo₂S₄//coal-based porous carbon?CPC?asymmetric supercapacitor?ASC?.Electrochemical measurements show that TiO₂@NiCo₂S₄//CPC not only has high energy density and power density(41.6 Wh kg^-1 at 400W kg^-1),but also has good cycle stability(after5000 cycles at 4 A g^-1).The capacitance retention rate is 82.5%).Secondly,based on the flexible carbon cloth cleaned by plasma,TiO₂ nanowire arrays were grown on the surface of carbon cloth by step-by-step hydrothermal method,and then the NiCo₂S₄ nanosheet were grown on the basis of the nanowires.Fabrication of core/shell array structure of TiO₂ nanowires coated with NiCo₂S₄nanosheet.Using NTC as a binder-free and conductive electrode for supercapacitors,the electrochemical performance of the electrode was studied by three electrodes.The results show that the specific capacitance of NTC electrode reaches 900F g^-1 at 1 A g^-1.When the current density is from 1 A g^-1 to 5 A g^-1,the specific capacitance can be kept at 75%,and the specific capacitance can still be maintained at 95%after 10000charge-discharge cycles at 5 A g^-1,which indicates that the NTC electrode has a higher specific capacitance,good rate performance and excellent cycle stability.The reasons may be due to the high conductivity of TiO₂,the short ion transport channels in core-shell structure,and the synergistic effect between many reactive sites in NiCo₂S₄ nanosheet.In addition,the carbon nanotube array?CNT@C?was used as the negative electrode and the NTC as the positive electrode to assemble the NTC//CNT@C asymmetric supercapacitor?ASC?.Electrochemical measurements show that NTC//CNT@C not only has a high energy density and power density(0.24mWh cm^-2 at 3.1 mW cm^-2),it also has good cycle stability(after 5000 cycles at 5mA cm^-2,the capacitance retention rate is 85%).According to the results of electrochemical measurement,it is proved that the NTC//CNT@C flexible asymmetric device is an excellent electrode material for flexible supercapacitors with high performance.Thirdly,based on the flexible carbon cloth cleaned by plasma,the NiGa₂O₄nanosheet was grown on the surface of the carbon cloth by hydrothermal method,and then the MnO₂ nanosheet was grown on the basis of it.The core-shell array structure?MnO₂@NiGa₂O₄@C cloth abbreviated MNC?,NiGa₂O₄ nanosheet coated with MnO₂ nanosheet was obtained.MNC was used as a binder-free and conductive electrode for supercapacitors.The electrochemical performance of the electrode was studied by three electrodes.The results show that the specific capacitance of MNC electrode reaches 1700 F g^-1 at 1 A g^-1.When the current density is from 1 A g^-1 to 15A g^-1,the specific capacitance can be maintained at 70%,and the specific capacitance can still be maintained at 90%after 10000 charge-discharge cycles at 20 A g^-1,which indicates that the MNC electrode has a higher specific capacitance,good rate performance and excellent cycle stability.The reasons may be due to the high conductivity of NiGa₂O₄,the short ion transport channels in core-shell structure,and the synergistic effect between NiGa₂O₄nanosheet and MnO₂ nanosheet.In addition,nitrogen-doped mesoporous carbon?N-CMK?and CNT@C were used as negative electrode and MNC as positive electrode to assemble MNC//N-CMK and MNC//CNT@C asymmetric supercapacitor?ASC?.Electrochemical measurements show that MNC//N-CMK has excellent energy density and power density(25 Wh kg^-1at 800 W kg^-1),and MNC//CNT@C has excellent power density and energy density(0.26 mWh cm^-2 at 2.5 mW cm^-2).It also has good cycle stability(after 5000 cycles at 3 A g^-1,the capacitance retention rate is 80%).According to the results of electrochemical measurement,it is proved that the MNC//CNT@C flexible asymmetric device is an excellent electrode material for flexible supercapacitors with high performance.