The Preparation And Electrochemical Capacitance Performance Study Of Cobalt-basde Nanoarrays

Supercapacitors have been regarded as one of the most promising candidates for rechargeable energy storage devices with the advantages of high power density,fast charging capability,safety and reliability.Electrode materials play an important role in various factors affecting the performance of supercapacitors.Therefore,it is critical to design and prepare the electrode materials with excellent electrochemical properties for supercapacitors.Cobalt-based metal oxides,as the most ideal cathode materials for supercapacitors,have the advantages of extremely high theoretical specific capacitance,abundant reserves,low cost,environmentally friendly and non-toxic properties.However,the actual capacitance was tend to be much lower than the theoretical value,which is due to their low conductivity.In order to overcome the above shortcomings,the cobalt-based self-supported nanoarrys electrode materials with excellent electrochemical performance for supercapacitors were prepared by designing the structure of electrode materials in this paper.The specific research contents of the thesis are as follows:?1?The uniform MnCo₂O₄ nanowire arrays were synthesized directly on the Ni foam via a facile hydrothermal method followed by annealing treatment.A single nanowire exhibited a shape of cone.The as-synthesized MnCo₂O₄ electrode exhibited excellent electrochemical performance,which can be attributed to the wonderful conductivity between Ni foam and active materials and avoiding the use of the binder.More specifically,the specific capacitance of MnCo₂O₄ nanowire arrays exhibited 1.79 F·cm^-2at a current density of 1 mA cm^-2,and a capacitance retention of 80.84%after 6000 cycles at a current density of 10 mA cm^-2.?2?The core-shell MnCo₂O₄@NiWO₄ nanoarrays were successfully grown directly on the Ni foam via a two-step hydrothermal process associated with successive annealing treatment.NiWO₄ was encapsulated on the surface of MnCo₂O₄ as a shell layer,which significantly improves the electrochemical performance of the core layer.The as-prepared core-shell MnCo₂O₄@NiWO₄ nanoarrays has a specific capacitance of 5.09 F cm^-2 at a current density of 1 mA cm^-2 and maintained an excellent cycle stability.Furthermore,an asymmetric supercapacitor which was fabricated by using the MnCo₂O₄@NiWO₄electrode as the positive electrode and the activated carbon as the negative electrode exhibited a prederable energy density of 0.23 mW·cm^-2 and power density of16 mW·cm^-2.The excellent electrochemical performances indicate the promising potential application of core-shell MnCo₂O₄@NiWO₄ nanoarrays.?3?The Mn-doped NiCoP nanoarrays with the hierarchical structure were prepared on the Ni foam by hydrothermal method and chemical vapor deposition method.It can be seen from the experimental results that the prepared multi-metal phosphide exhibits a high specific capacitance of 7.88 F·cm^-22 at the current density of 2 mA·cm^-2.And when the current is expanded by 25 times to 50 mA·cm^-2,the specific capacitance of the material is still as high as 4.8 F·cm^-2.The material demonstrates remarkable electrochemical specific capacitance and superior rate capability.