The Preparation And Supercapacitor Performance Study Of Heterogeneous Nickel/Cobalt-based Nanowire Arrays

Supercapacitors,with the advantages of high power density,long cycle life and rapid charging and discharging processes,have attracted more attention from researches.Nevertheless,the poor energy density and low voltage window still limit the application of supercapacitors in various fields.Thus,the development of electrode materials with the characteristics of low cost,high energy density and large voltage window is very essential for the application of supercapacitors.The nanostructure of nickel-cobalt bimetallic compounds and their relationship with electrochemical properties were systematically studied.Nickel-cobalt hydroxide precursor was produced by the hydrothermal method.Two electrode materials,Ni Co₂O₄ and CoO-Ni₃N,were produced by annealing in air and ammonia atmosphere,respectively.Different from Ni Co₂O₄ with a single-phase structure,the precursor after nitriding became a heterogeneous structure composed of CoO and Ni₃N.Since the bandgap of Ni₃N was approximately 0 e V,the electronic conductivity of electrode materials could be improved.In addition,the large difference between CoO and Ni₃N in bandgaps would causes the transfer of from the CoO side to the Ni₃N side nearby the heterointerfaces,which could increase the carrier concentration and the amount of active sites.Moreover,the redistribution of electrons would form a built-in electric field at the heterogeneous interface,and thus to improve the depth of redox reactions.As a result,the CoO-Ni₃N heterostructures delivered the ultra-high areal specific capacity of 3800 m F cm^-2 at 5 m A cm^-2.Even at a high rate of 30 m A cm^-2,the heterostructures electrode still remained the specific capacity of 2311 m F cm^-2 after 5000 cycles,demonstrating the superior capacity and excellent rate performance.Meanwhile,in order to expand the practicability of CoO-Ni₃N heterostructures,this paper assembled CoO-Ni₃N and activated carbon（AC）into an asymmetric solid-state supercapacitor（CoO-Ni₃N//AC ASC）,and tested the supercapacitor performances.The AC electrode enlarges the voltage window of the supercapacitor,while the CoO-Ni₃N electrode increases the capacity of the supercapacitor.Under the large current density of 80 m A cm^-2,CoO-Ni₃N//AC ASC can reach the area ratio capacity of 210.3 m F cm^-2,and still maintain the initial capacity of 91.2%after10,000 charge and discharge cycles.Even at a high power density of 35.9 m W cm^-2,the CoO-Ni₃N//AC ASC still remain the excellent energy density of 0.115 m Wh cm^-2.The power density and energy density of CoO-Ni₃N//AC ASC are superior than that of the previously reported nickel-cobalt hydroxide asymmetric supercapacitor.The above methods of generating heterostructures from bimetallic compounds and the analysis of energy storage characteristics can provide the theoretical and experimental guidance for the modification of other bimetallic compounds.