Preparation Of Nickel Cobalt Metal Compounds Free-standing Electrodes And Their Electrochemical Storage Application

Supercapacitors have the advantages of fast charge/discharge,high power density,and long-cycling life.Nickel foam（NF）is a cheap commercial material with high electrical conductivity and ideal 3D open-cell structure,which makes it as a common support for electrode materials.Transition metal compounds can offer high specific capacitance but suffer from low rate capacibity.We can solve this problem by well adjusting the structure and composition.Therefore,we have designed and developed two types of nickel foam-based transition metal compounds free-standing electrodes with ultra-high rate capability.The specific contents are as follows:（1）Firstly,we prepared crystalline Ni Se-Ni3S2 triangular prism microarrays on nickel foam via a solvothermal method.Then the amorphous Ni-Co bimetallic hydroxides nanosheets were further prepared to uniformly cover the surface of Ni Se-Ni3S2.By taking advantage of the unique structure and synergistic effect between crystalline and amorphous transition metal compounds,the as-prepared Ni（OH）2-Co（OH）2/Ni Se-Ni3S2/NF exhibited an ultra-high specific areal capacitance（CA）of19.01 F cm^-2 at a current density of 15 m A cm^-2,along with an excellent rate capability of 51.6%at even 100 m A cm^-2.The capacitance retention was 88.4%after 4000 cycles at the current density of 100 m A cm^-2.With activated carbon on NF as the negative electrode,we assembled hybrid supercapacitor devices that achieved a high volumetric energy density of 13.9 m Wh cm^-3at a power density of 200 m W cm^-3.（2）The Ni-Co selenide sample based on nickel foam was prepared through a template sacrificing method.First,two-dimensional amorphous Co（OH）2-Ni（OH）2nanosheets were electrodeposited on the surface of nickel foam at a constant potential.Then a Na2Se O3 solution prepared by solvothermal reaction was used to etch the hydroxide ion to realize solvothermal selenization.Co Se2-Ni Se/NF electrode obtained by selenization using two-dimensional amorphous nanosheets as templates can provide more active sites.The CA value was calculated to be 17.4 F cm^-2(15 m A cm^-2).As the current density increased to 125 m A cm^-2,the rate capability was 67.3%.The capacitance retention was 86.6%after 4000 cycles at 100 m A cm^-2.In general,nickel cobalt metal compounds free-standing electrodes based on nickel foam have ultra-high specific areal capacitance and excellent rate capability,which will promote the further development of binder-free energy storage devices.