Synthesis And Electrochemical Performance Of Nickel Foam-Based As Electrode Materials For Supercapacitors

Supercapacitors,one of the branch of energy storage devices,have attracted extensive attention not only in academia but also in industry for prominent advantages,including higher energy density than conventional capacitors as well as greater power densities,longer life spans and much more excellent charge/discharge properties than lithium-ion batteries.Among all the reported active electrode materials,the nanostructured transition-metal electrodes exhibit exceptionally higher specific capacitance and energy density that surpass activated carbon materials.Ni foam,a most commonly used three dimensional?3D?skeleton structure material,with the characters of exceptional uniformity,light weight,high porosity,corrosion resistance,excellent electrical and thermal conductivity is wildly used as substrates?current collector?in the field of electrode fabrication of supercapacitors.The conventional electrode preparation is to make the mixture of the active material,the conductive agent and the binder adhere to the the surface of the current collector by a tableting technique.The additional blinder increases the internal resistance of the electrode and inevitably reduces the overall specific capacitance of the electrode.In this paper,nickel foam is treated as the research object,and the active materials are directly deposited on the surface of nickel foam by two types of methods.Nickel foam,firstly,serves as current collector,of which the active material is in-situ grown on the surface.The ZnCo₂O₄@NiWO₄ core/shell structure is fabricated on Ni foam by two steps hydrothermal treatment followed with calcination.The ZnCo₂O₄@NiWO₄ composites present good electrochemical performance and the areal capacitance achieves as high as 2.140F cm^-2 at the current density of 1 mA cm^-2.The capacitance retention still remians95.40%after 5000 cycles of cyclic testing.In order to further reduce the series resistance of the electrode,Mn-Co-S composites are successfully deposited on Ni foam by a cyclic voltammetry method with a three-electrode system at a scan rate of 5 mV s^-1 for 20 cycles.The composite electrode shows great electrochemical properities and the areal capacitance is 1.724 F cm^-2 at a low current density of 1mA cm^-2.After 5000 cycles of continuous charge and discharge test,the retention of areal capacitance is 65.15%.In addation,the the series resistance of the electrode has been improved.However,the active materials on Ni foam prepared by in-situ growth methods suffer from falling off the current collector during the test.Therefore,this paper adopts a method where the nickel foam not only serves as current collector but also as nickel source,and the nickel atoms on the surface of Ni foam are directly oxidized to active materials.Hexagonal prism-like Ni?OH?₂ microrods are fabricated on Ni foam by a simple hydrothermal method,using H₂O₂ as oxidant.The electrode demonstrates an areal capacitance as high as 2.91 F cm^-2 at a current density of 1 mA cm^-2,the areal capacitance of which can preserve 72.90%after 3000 cycles of continuous charge and discharge test.And the electrode exhibites a relatively small series resistance.To gurantee the small series resistance and the cycling stability of the electrode,hexagonal plate-shape Ni?OH?₂-NiFe₂O₄ composite electrode material is successfully grown on Ni foam by a simple hydrothermal method,using Fe?NO₃?₃ as oxidant.The electrode exhibits an areal capacitance of 1.43 F cm^-22 at a current density of 1 mA cm^-2 and keeps the low the series impedance.The capacitance retention is 75.90%after5000 charge and discharge cycles.