The Preparation And Supercapacitor Performances Of MCo₂O₄?M=Ni,Cu,Zn?

This thesis mainly focuses on the design and the synthesis of the cobaltate-based micro/nanomaterials for the applications as high performance supercapacitor materials.The main results are as follows:1.High-performance NiCo₂O₄ NNAs on nickel foam and carbon fabric have been successfully prepared by a one-step facile hydrothemal process followed by annealed treatment in an air atmosphere,which were directly used as the work electrodes to examine their electrochemical properties.As the results shows that the specific capacitance of NiCo₂O₄ NNAs/N.F.reached 655 F g^-1 at 1 A g^-1,even 544 F g^-1 at a high current density of 20 A g^-1,which exhibit excellent rate performance of 83% retention.Furthermore,the specific capacitance and rate performance of NiCo₂O₄ NNAs/N.F.are better than the NiCo₂O₄ NNAs/C.F.,which demonstrate that the conductivity of the substrates have great influence on the performance.After 4000 cycles,the capacitance still retains 81% of the initial.2.Two-step hydrothermal method has been developed to successfully synthesize hierarchical NiCo₂O₄@Ni_0.5Co_0.5MoO₄?NCO@NCMO?core/shell nanoarchitectures.The SEM and TEM characterizations proved the formation of NCO@NCMO core/shell nanoarchitectures.Then,the NCO@NCMO core/shell nanoarchitectures were directly used as a working electrode,and investigated by electrochemical workstation with three electrodes.The results demonstrated excellent electrochemical performance,exhibiting the specific capacitance of 761 m F cm^-2 at 2 m A cm^-2,higher than that of NCO NNAs(477 m F cm^-2).These results manifested that the performances of these NCO@NCMO core/shell nanoarchitectures were greatly inhanced.3.Ni_0.5Co_0.5?OH?₂ nanosheets coated Cu Co₂O₄ nanoneedles arrays were successfully designed and synthesized on carbon fabric.Highly uniform and stabled Cu Co₂O₄ nanoneedles arrays were synthesized and directly used as efficient conductive scaffold,and the Ni_0.5Co_0.5?OH?₂ ultrathin nanosheets were deposited on them by electrodeposition method,which increase the specific surface areas and provide more electrochemical active sites to enhance the electrochemical performance.As the results show that the Cu Co₂O₄@Ni_0.5Co_0.5?OH?₂ core/shell nanoarchitectures delivered excellent specific capacitance of 1935 F g^-1 at 1 A g^-1,which still maintained 1497 F g^-1 even at the high current density of 40 A g^-1,manifesting their remarkable rate capability.The as-assembled Cu Co₂O₄@Ni_0.5Co_0.5?OH?₂//AC asymmetric supercapacitor device exhibited favorable properties with the specific capacitance as high as 90 F g^-1 at 1 A g^-1 and the high energy density of 32 Wh kg^-1 at the power density of 800 W kg^-1.What's more,the as-assembled device delivered excellent cycling performance(retaining 91.9 % of the initial capacitance after 12000 cycles at 8 A g^-1),robust mechanical stability and flexibility,implying the huge potential of present hierarchical electrodes in energy storage devices.4.Zn Co₂O₄ nanoneedles arrays?ZCO NNAs?on nickel foam were successfully synthesized by hydrothermal and calcination method.Then,the ZCO NNAs were directly treated as working electrodes to grow nickel-cobalt sulfide?NCS?nanosheets in order to form ZCO@NCS core/shell nanoarchitectures.The ZCO NNAs possessed high conductivity and structural stability,and NCS nanosheets as the shell with high specific surface area and amount of active sites,which greatly enhanced the electrochemical performance.The ZCO@NCS core/shell nanoarchitectures displayed high capacitance of 700 F g^-1 at 1 A g^-1,higher than the 273 F g^-1 of ZCO NNAs,manifesting it is feasible to adopt these ZCO@NCS core/shell nanoarchitectures to inhanced the electrochemical performances.