Synthesis And Electrochemical Properties Of Nickel-based Ternary Transition Metal Oxides/Sulfides Composite Electrode Materials

With the increasing demand for energy,the reserves of traditional fossil fuels are decreasing and environmental pollution is increasing.To alleviate these problems,wind,light,and tidal energy are converted into electricity currently,which is very unstable due to environmental changes and regional differences.Therefore,a new type of device is urgently exploited for energy conversion and storage.Supercapacitors have shown great superiorities among many electrochemical energy storage devices due to their advantages of eco-friendliness,low cost,facile preparation,low influence by ambient temperature,high specific capacitance,high power density,fast charge-discharge rate and long cycling lifespan.Electrode materials,as the centre of supercapacitor,are focused by many researchers.Currently,the research mainly focuses on pseudocapacitance high-performance electrode materials,among which transition metal oxides/sulfides are considered to be the most promising electrode materials.In this paper,nickel-based ternary transition metal oxides/sulfides composite electrode materials with different morphologies and components were prepared on Ni foam by hydrothermal methods,and then used as electrode materials to investigate their electrochemical properties.The main contents and results of this paper are as follows:(1)The core-shell structured Ni Co₂O₄@Mn Mo O₄ nanosheet hybrid arrays were directly grown on the Ni foam conductive substrate through two-step hydrothermal reaction and calcination treatment,and their electrochemical properties were investigated.The composite electrodes with layered nanosheet structure could effectively improve the electrochemical performance of the electrodes by combining the advantages of both materials.The composite electrode had the most obvious core-shell structure as the second hydrothermal reaction time was 4 h,and exhibited the highest specific capacity of 1205.75 C g^–1 at a current density of 1 m A cm^–2 and excellent capacity retention rate of 100.49%after 5000 cycles at 30 m A cm^–2.Serving the optimal sample as the positive electrode,the asymmetric supercapacitor(ASC)was assembled,which possessed the maximum energy density of 39.04 W h kg^–1,maintained the energy density of 34.12 W h kg^–1 at the power density of 1568.74 W kg^–1 and remained 95.00%of its initial specific capacitance after 10000 cycles at 20 m A cm^–2.(2)Using two-step simple hydrothermal reaction,as well as adjusting the conditions of the second-step sulfurization reaction,the effects of reaction concentration,reaction temperature,and reaction time on the compositions,morphologies,and electrochemical properties were respectively explored.By comparing the experimental results of the samples obtained under different reactions,it was found that as the reaction was maintained at 120?for 12 h in 0.1 M Na₂S solution,the obtained electrode only had the single component of Ni Co₂S₄ and presented the microstructure of hollow nanotubes with a smooth and complete surface.Using the optimal sample as the electrode for electrochemical test,the following results were obtained:It displayed high specific capacity of 580.00 C g^–1 at a high current density of 50 m A cm^–2,as well as desirable cycling stability,retaining 88.09%of its initial capacity after 5000 cycles at a high current density of 50 m A cm^–2.(3)The NiCo₂S₄ nanotube@Ni Mn-LDH nanosheet hybrid arrays with core-shell structure were directly prepared on Ni foam by three-step hydrothermal reaction.The growth density of Ni Mn-LDH nanosheet shell layer could be regulated by adjusting the time of the third-step hydrothermal reaction.As the third hydrothermal time was 6 h,the prepared Ni Co₂S₄@Ni Mn-LDH had the most distinct core-shell morphology and demonstrated the best electrochemical performance,which exhibited a high specific capacity of 822.64 C g^–1(4.36 C cm^–2)at a high current density of 50 m A cm^–2 and maintained 92.72%of the initial capacity after 5000 cycles of charge-discharge at the same current density.In addition,the ASC device assembled with this electrode as the positive electrode and activated carbon(AC)as the negative electrode manifested an energy density of 53.10 W h kg^–1 at a power density of 370.82 W kg^–1 and a capacitance retention rate of 94.30%after 10000 cycles at a current density of 20 m A cm^–2.In this paper,high-performance electrode materials with various morphologies were prepared by different reaction routes,which provide a new path for the design and preparation of high-performance supercapacitors.