The Synthesis And Electrochemical Properties Of Transition Metal Compounds Core-shell Nanomaterials

Due to the unique physical and chemical properties,and rich in natural reserve,the transition metal compounds have been active in daily application and scientific research,particularly in catalysis,energy storage,electromagnetic,sensing and other fields.More and more research institutions and universities are dedicated to the synthesis of transition metal nanomaterials to improve the performance of materials.In many transition metal compounds,Cd,Co,Mn,Ni chalcogenide nanomaterials have become the research hot spot,owing to the stable nanometer structure and excellent electrochemical performance.And these advantages can just satisfy the scientists for the study of supercapacitor materials.Through ion exchange method and hydrothermal method,a series of nano-materials with unique structure and excellent electrochemical properties of transition metal Cd,Co,Mn and Ni had been synthesized in this paper.The main research contents of this paper are:1.One dimensional hierarchical MnO₂@NiCo₂O₄ core-shell nanostructures were successfully prepared by a facile two-step hydrothermal method.As supercapacitor electrode,it exhibits a high capacitance of 684 F g^-11 at a current density of 2 A g^-1,and can retain 87.7%at a high current density of 15 A g^-1,indicating excellent rate capability.In addition,an asymmetric supercapacitor is assembled with MnO₂@NiCo₂O₄ as the cathode electrode and porous carbon as the anode electrode and KOH solution as the electrolyte.It exhibits a high capacitance of 115 F g^-1at a current density of 1 A g^-1,as well as a good cycling life with 90%retention rate after 7000 cycles at a current density of 4 A g^-1.Thereby,theseelectrochemicalperformancesdemonstratedthatas-fabricated MnO₂@NiCo₂O₄ core-shell nanostructures can be the promising candidates for high-performance supercapacitors.2.In this work,we successfully design and synthesize the hierarchical NiCo₂O₄@NiCo₂S₄ core-shell nanowire arrays on Ni foam by an special interface ion-exchange process.As supercapacitor electrode,it exhibits a high specific capacitance of 3176 F g^-11 at a current density of 2 A g^-11 and can retain 86.52%at a high current density of 10 A g^-1,indicating excellent rate capability.In addition,an asymmetric supercapacitor is assembled with NiCo₂O₄@NiCo₂S₄ as the cathode electrode and porous carbon as the anode electrode and KOH solution as the electrolyte,showing a super energy density of196.8 Wh k g^-11 at 752.33 W k g^-1.After 15000 cyclic voltammetry cycles at a scan rate of60 mV s^-1,137%of initial capacitance is maintained.Thereby,these electrochemical performances demonstrated that as-fabricated NiCo₂O₄@NiCo₂S₄ core-shell nanowire arrays are the promising candidates for high-performance supercapacitors.3.Hierarchical Ni₃S₂@CdS core–shell nanostructures on nickel foam were synthesized by a one-step hydrothermal method for the first time.As supercapacitor electrode,the Ni₃S₂@CdS core–shell nanostructures exhibited a high capacitance of 3.15 F cm^-2(2100 F g^-1)at a current density of 2 mA cm^-2,and 86.7%of the original capacitance was retained even at a high current density of 15 mA cm^-2,suggesting excellent rate capability.An asymmetric supercapacitor based on Ni₃S₂@CdS as the positive electrode,porous carbon as the negative electrode and KOH as the electrolyte can work steadily at a voltage of 1.5V,and presented excellent electrochemical performance.After 4000 charge–discharge cycles at a current density as large as 6 m A cm^-2,130%of the initial capacitance was maintained.The asymmetric supercapacitor exhibited a high energy density of 127.5 W h kg^-11 at a current density of 2 mA cm^-22 and with a corresponding power density of 0.995kW kg^-1.The above-mentioned results indicate that Ni₃S₂@CdS could be a potential candidate for supercapacitors.