Application Research Of Zn/Co-MOF Derivative Composites In Supercapacitors

Supercapacitors(SCs),as a new type of energy storage conversion device,had shown great application potential in many fields.But its wider application was limited by its low energy density.In order to improve the energy density of supercapacitors,Zn/Co-MOF derivative composites with core-shell structure were prepared and used as the positive electrode to assemble the hybrid supercapacitor with excellent performance.Firstly,ZnCo₂O₄@NiCo₂S₄ core-shell nanosheets composite was prepared.Zn/Co-MOF-derived ZnCo₂O₄ nanosheets were grown directly on Ni foam(NF)via chemical bath deposition and annealing methods,then ZnCo₂O₄@NiCo₂S₄ core-shell nanosheets composite was prepared by cyclic voltammetry(CV)electrodeposition method.The electrochemical properties of the as-prepared materials were tested in a three-electrode system,and the influence of NiCo₂S₄ electrodeposition cycles(1,3,5)on the material performance was analyzed.The results indicated that the electrochemical performance of the as-prepared ZnCo₂O₄@NiCo₂S₄-5/NF electrode was better than others.The as-prepared ZnCo₂O₄@NiCo₂S₄-5/NF electrode exhibited the largest area capacitance(2.1221 F/cm²)and specific capacitance(1178.0 F/g)at current densities of 1 m A/cm² and 0.5 A/g,respectively;and its initial capacitance retention was still 90.4%after cycling 5000 times at a current density of 10 A/g.Second,ZnCo₂O₄@NiCo₂S₄@PPy core-shell nanosheets composite was prepared.The conductive polymer PPy was electrodeposited on the surface of ZnCo₂O₄@NiCo₂S₄ core-shell nanosheets by chronoamperometry electrodeposition method,in which the number of cyclic voltammetry electrodeposition of NiCo₂S₄ was5 times,ZnCo₂O₄@NiCo₂S₄@PPy core-shell nanosheets composite was prepared eventually.The electrochemical properties of the as-prepared materials were tested in a three-electrode system,and the effects of PPy electrodeposition time(20,40,60,80s)on the materials were analyzed.The results demonstrated that the as-prepared ZnCo₂O₄@NiCo₂S₄-5@PPy-60/NF electrode had the best electrochemical performance among the other as-prepared electrodes.The as-prepared ZnCo₂O₄@NiCo₂S₄-5@PPy-60/NF electrode exhibited the maximum surface capacitance(3.7480 F/cm²)at 1 m A/cm² and the maximum specific capacitance(2507.0 F/g)at 0.5 A/g.Furthermore,it still retained 83.2%of the initial capacitance after 5000 cycles at the current density of 10 A/g.Finally,a coin-type hybrid supercapacitor was assembled by employing the as-prepared ZnCo₂O₄@NiCo₂S₄-5@PPy-60/NF as positive electrode and activated carbon(AC)as negative electrode.The electrochemical performance of the as-assembled HSC device was tested in a two-electrode system.The results suggested that the as-assembled HSC device displayed a high energy density of 44.15 wh/kg at the power density of 850 W/kg and exhibited 80.7%capacitance retention after 3000cycles at the current density of 5 A/g,which showed excellent energy storage performance.