Study On Preparation Of NiCo₂O₄ Composite Transition Metal Oxide And Its Supercapacitor Performance

The recent growth in multifunctional consumer electronics and the electrification of transportation,the development of cost-effective renewable energy materials and devices has become one of the researching hotspots of materials science currently.Supercapacitor has the advantages of high power density,long cycle life and environmental friendliness,etc,but the low energy density severely restricted its large-scale development,therefore,the study of high capacitance,high power,long life of the new supercapacitor is of great significance.Electrode materials play an important role in the properties of supercapacitor,the synthesis and construction of high-performance electrode materials depends on the optimization of the different morphologies and the coordination between the different types of composite electrode materials.In order to enhance the assembly of the super capacitor energy density,develop an asymmetric supercapacitor(ASC)composed of an inexpensive pseudo-capacitive metal oxide electrode and a capacitive electrode,thereby extending its operating voltage window.The main results are as follows:Firstly,NiCo2O4(NCO-NS)and NiCo2O4 nanowires(NCO-NW)arrays were synthesized by simple and moderate chemical coprecipitation method and controlling the reaction parameters.The electrochemical performance of the material was investigated by cyclic voltammetry,constant current charging and discharging,AC impedance test.The results show that the maximum area specific capacitance of NCO-NS and NCO-NW is 5.06 F cm-2 and 5.60 F cm-2 at current density of 2 mA cm-2.When the current density increased from 2 to 20 mA cm-2,the capacitance retention rate of NCO-NS was 70%and the NCO-NW retention rate was 45.18%.Secondly,NiCo2O4/Co3O4 nanosheets were prepared by chemical coprecipitation method and hydrothermal method.The composition and structure of NiCo2O4 and Co3O4 nanosheets were characterized by XRD,SEM,TEM and BET.The NiCo2O4 and NiCo2O4/Co3O4 nanosheets array of supercapacitor performance,and compared the supercapacitor performance of NiCo2O4 and NiCo2O4/Co3O4 nanosheet array,high porosity and good structural stability.When the current density is 2mA Ccm-2,the area specific capacitance delivers 6.05 F cm-2,and Only 6.2%of the capacitor is lost after 1500 cycles.Finally,the bio waste-derived hierarchical porous carbon(Bio-HPC)was prepared by carbonization and activation pyrolysis of corncob.The different structures of NiCo2O4 nanoarray as positive,Bio-HPC as the negative,polypropylene as the diaphragm material,30 wt%KOH as the electrolyte,were assembled into excellent performance of the asymmetric supercapacitor.The NCO-NW//Bio-HPC ASC delivers a higher energy density of 54.44 Wh kg-1 at a power density of 124.99 W kg-1,while the NCO-NS//Bio-HPC ASC exhibits better cycling stability(a capacitance loss of only approximately 8.88%after 2000 cycles).