Preparation Of Transition Metal Sulfide And Their Capacitance Performances

Energy issue becomes the first challenge facing humanity in modern society.With the continuous exhaustion of fossil energy and the increasingly serious environmental pollution caused by the consumption of fossil energy,renewable energy has to be developed and used such as solar energy,wind energy,tidal energy,biomass energy and so on.However,in the process of renewable energy utilization,energy storage devices are urgently needed.At present,batteries and supercapacitors are the main electrochemical ways to store electrical energy.Although the capacity of the battery is at least one order of magnitude larger than that of the supercapacitors,the supercapacitors with the advantages of fast charging rate,high power density,long cycle life and safety is especially suitable for urban traffic and power station peak regulation.However,the problem of low energy density must be solved for supercapacitors to achieve large-scale commercial applications.Currently,the energy density of commercial supercapacitors is only 6?9 Wh kg^-1,which is far from meeting the demand for the development of human society.The deciding factor is electrode materials for improving the energy density of supercapacitors.Therefore,it is inevitable for developing high-performance supercapacitors to find electrode materials with high theoretical capacity,stable performance,low price and friendly environment,which has important practical significance.Unlike the energy storage mechanism of battery,supercapacitors mainly rely on the surface layer to store electricity.Whether it is electric double-layer capacitor or pseudocapacitor,electrical energy storage occurs on the surface layer of energy storage materials.Therefore,it is the starting point of this study to develop nanomaterials with large specific surface area,good conductivity,stable structure and hierarchical structure.Based on this idea,the transition metal sulfide with high theoretical capacity and good conductivity was selected as the research object and carried out in this paper.?1?NiCo₂S₄ nanomaterials were synthesized via a room temperature stirring process and high temperature reflow method.SEM,XRD and TEM measurements indicated that NiCo₂S₄presented a nanoscale structure of hollow cube with nanosheets on the surface.The electrochemical test results indicated that the NiCo₂S₄ electrode had a specific capacitance of1356 F g^-1 at a current density of 1 A g^-1.The specific capacitance decreases with the increase of the current density.The specific capacitance dropped to 950 F g-1 when the current density increased to 20 A g^-1,but still had ca 70%retention,presenting a relatively good rate capability.A hybrid supercapacitors?PC//NiCo₂S₄?was assembled with NiCo₂S₄ electrode as positive electrode and porous carbon as negative electrode,which exhibited a maximum energy density of 33 Wh Kg^-1 at a power density of 800 W Kg^-1 and a good cyclic stability of 67%capacitance retention after suffering from charge-discharge cycles of 10000 times at the current density of5 A g^-1.?2?The Co₉S₈@Ni?OH?₂ electrode material with unique shell-core structure was prepared by in situ growth of Co₉S₈ nanosheets on nickel foam by hydrothermal method,and then growth of Ni?OH?₂ nanosheets on the surface of Co₉S₈ by electrochemical deposition.The electrochemical test results indicated that the Co₉S₈@Ni?OH?₂ electrode had a high specific capacitance of 1922 F g^-1 at a current density of 1 A g^-1.The specific capacitance decreases with the increase of current density,and the specific capacitance was 1039 F g^-1 when current density increased to 20 A g^-1.After 1000 charge-discharge cycles at a current density of 5 A g^-1,the specific capacitance retention rate is 60.3%.The hybrid all-solid supercapacitors?PC//Co₉S₈@Ni?OH?₂?was assembled by using Co₉S₈@Ni?OH?₂ electrode as positive and porous carbon as negative electrode,exhibited a maximum energy density of 36.7 Wh kg^-1 at a power density of 799.9 W kg^-1 and superior cycling stability with the capacitance remained83.3%after 10000 charge-discharge cycles at 5 A g^-1.?3?The self-supporting porous Co₃S₄ nanosheet electrode was prepared by one-step hydrothermal method using deionized water and ethylene glycol as solvent,cobalt acetate as cobalt source,thiourea as sulfur source and nickel foam as electrode substrate.The electrochemical test results indicated that the Co₃S₄ electrode exhibited excellent electrochemical performance with a high specific capacitance of 2460 F g^-1 at a current density of 1 A g^-1 and capacitance retention of 63%(1544 F g^-1 at 20 A g^-1).