Study On Synthesis Of Ni-Co Double Metal Hydroxide Self-supporting Electrode And Its Electrochemical Performance

Due to unique features such as high power density,fast charging time,long life span,high safety level and environmental compatibility,the supercapacitor has been conceived as an efficient energy storage device.The performance of supercapacitors mainly depends on the material composition and structure of the electrode.Nickel-cobalt double metal hydroxide can be used to obtain the synergistic effect of nickel and cobalt and has been considered to be a promising material for pseudocapacitor.Most of the traditional electrode materials are powders and the polymer binders or other conductive additives should be added in the process of preparing electrodes,which influence the full contact of the electrolyte with electrode materials and reduce the utilization of active materials.Therefore,in this paper,the Ni_xCo_1-x?OH?_y nanosheet self-supporting electrodes and 3D ZnO@Ni_xCo_1-x?OH?_y nanowire@nanosheet arrays self-supporting electrodes were prepared,which would ensure more material involved in the faradic redox reaction,thus improving the electrochemical performance of the electrodes.In the first part of this paper,Ni_xCo_1-x?OH?_y nanosheets were synthesized on the surface of nickel foam by potentiostatic electrochemical deposition method.The physical properties of the electrodes were studied by XRD,XPS,SEM,TEM and electrochemical behaviors of the electrodes were also investigated.We discussed the effects of the deposition time and the ratio of Ni to Co of the electroplating solution on the morphology,structure and electrochemical properties of the electrode materials.The electrochemical test results show that the best deposition time of Ni_xCo_1-x?OH?_y nanosheets is 2 min.And when the ratio of Ni to Co is 2:1,the specific capacitance of the prepared Ni_0.67Co_0.33?OH?_y nanosheet electrode is 1580 F g^-1 at a current density of1 A g^-1,but the specific capacitance retention rate is only 57%when the current density increases to 50 A g^-1.The rate capability of the electrode is not ideal and it needs to be further improved.In the second part of this paper,a novel electrode featuring three-dimensional?3D?hierarchical ZnO@Ni_xCo_1-x?OH?_y nanowire@nanosheet arrays arranged on Ni foam substrate was designed and synthesized via a two-step protocol including a wet chemical process followed by electro-deposition.The composition,structure and surface morphology of the hybrid electrodes were characterized by XRD,EDS,XPS,SEM,TEM and electrochemical tests were also studied.We discussed the effects of the size of ZnO nanowires and the ratio of Ni to Co of the electroplating solution on the morphology,structure and electrochemical properties of the electrode materials.The electrochemical test results show that the optimal reaction time of the ZnO nanowire arrays which were used to prepare 3D ZnO@Ni_xCo_1-x?OH?_y nanowire@nanosheet arrays is 9 h.And when the ratio of Ni to Co is 2:1,the specific capacitance of the prepared 3D Zn O@Ni_0.67Co_0.33?OH?_y nanowire@nanosheet arrays electrode is in 1836 F g^-1 at a current density of 1 A g^-1 and the specific capacitance retention rate is 81.2%when the current density increasea to 50 A g^-1.Moreover,the capacitance retention rate of 3D ZnO@Ni_0.67Co_0.33?OH?_y nanowire@nanosheet arrays electrode is 81.6%after 2000 cycles at a current density of 5 A g^-1.