The Preparation And Electrochemical Performance Of Transition Mn/Co Based Composite Electrodes

Supercapacitors have attracted considerable attention duo to their wide application in portable electronics,hybrid electric vehicles,and smart electricity grids.Compared with carbon-based supercapacitors,pseudocapacitive materials can provide higher specific capacities and energy densities due to the efficient reversible redox reaction.Recently,transition metal oxide/hydroxyl,selenide and sulfide have been condidered as the most promising electrode materials for supercapacitor because they can increase the electrochemical performances synergistically in terms of reversible,structural stability,and electrical conductivity.Among them,manganese-cobalt binary metallic compounds have attracted extensive attention due to their good conductivity and electrochemical activity.However,the practical application of Mn-Co electrode materials is still hindered by their relatively low specific capacitance and poor cycle stability.In order to solve this problem,a reasonable composite materials or composite nanostructure can be designed,which can not only maintain the excellent properties of the original material,but also combine the advantages of other materials to achieve synergistic effect and improve the electrochemical properties of the electrode material.In this paper,we have successful synthesizedmanganesecobaltselenide/reductiongraphemeoxide?MCSe/rGO/NF?,manganese cobalt sulfide/reduction grapheme oxide?MCS/rGO/NF?and manganese cobalt hydroxide/reduction grapheme oxide@nickel cobalt sulfide?MC-L/rGO@NCS?,and their morphology structure and electrochemical properties have been investigated.In addition,the application of these electrode materials in supercapacitors has been investigated.The main contents are as follows:?1?Mn-Co-Se/rGO/NF composites were prepared by chemical precipitation and two-step hydrothermal methods.The effects of different reaction time on the morphology and electrochemical properties of the electrode materials were studied.According to the measurement,MCSe/rGO/NF composites exhibited the optimum capacitance(2219 F g^-1 at 1 A g^-1)and excellent life span?98%after 5000 cycles?when the reaction time is 3 h.A hybridsupercapacitor?HSC?devicewasassembledusing Mn-Co-Se/rGO/NF-3h as positive and AC as negative,showing a high energy density of 45.8 Wh kg^-1 at a power energy of 853.1 W kg^-1.After 7000 cycles,the capacitance remains at 100%of the initial value.These results indicate that Mn-Co selenide is a potential electrode material.?2?We prepared MCS/rGO/NF composites via two-step hydrothermal method.As the reaction time increased,the thickness of MCS/rGO/NF nanosheet arrays charged from thin to thick.After 3 h of sulfurization reaction?MCS/rGO/NF-3h?,the composite showed the best electrochemical performance.MCS/rGO/NF-3h composite exhibited a large specific capacity of2712 F g^-1 at a current density of 1 A g^-1,and a long-term cyclic stability of 92.9%at a current density of 10 A g^-1 through 3000 cycles.Moreover,a HSC device was assembled using MCS/rGO/NF-3h and rGO as the positive and negative electrodes,respectively.The MCS/rGO/NF-3h//rGO HSC exhibited a high energy density of 45.4 W h kg^-1 at a power density of 850.2 W kg^-1.The prominent electrochemical performance suggests that the superiority of MCS/rGO/NF composites as an advanced electrode materials for supercapacitors.?3?The core-shell structure of MC-LDH/rGO@NCS composites is prepared by hydrothermal and electrochemical deposition methods.With the deposition cycle increased,the electrochemical properties of the composites also changed.When the deposition cycles is 6?MC-LDH/rGO@NCS-6?,the compositeexhibitedthebestelectrochemicalperformance.MC-LDH/rGO@NCS-6 composite achieved a high specific capacitance of 2893F g^-1 at 1 A g^-1,and displayed the excellent cycling stability about 98%after5000 cycles.Furthermore,a HSC based on MC-LDH/rGO@NCS-6 composite and active carbon electrodes showed outstanding performance with a high energy density of 55.8 Wh kg^-1 at a power density of 856.2 W kg^-1,and the specific capacitance could be retained at 100%after 6000 cycles,suggested that MC-LDH/rGO@NCS composite is expected to be the electrode material of the next generation of high-performance supercapacitors.