Synthesis And Electrochemical Properties Of Cobalt-based Ternary Transition Metal Oxide And Their Composite Electrode Materials

The rapid development of modern science and technology and people's daily life rely on the use of various electronic products and energy,how to achieve efficient energy storage is a major challenge in the field of science in this century.Supercapacitors?SCs?have many advantages as an energy storage device.,and electrode materials are one of the cores of SCs.Therefore,the design and synthesis of high-performance electrode materials have attracted much attention.Metal oxide materials have high electrochemical performance due to their pseudocapacitance reaction mechanism.Compared with single metal oxides,ternary metal oxides have better electrochemical performance because they can be doped with other metal ions with rapid changing valence state.ZnCo₂O₄ relies on electron transfer between Co²⁺/Co³⁺ions to exhibit high pseudocapacitive properties.In addition,the pseudocapacitance of Ni?OH?₂ is derived from the charge transfer between Ni²⁺/Ni³⁺pairs,and the electrochemical properties are equally excellent.Therefore,it has been extensively studied by researchers.In this paper,metal nickel foam is used as a conductive substrate,we design and synthesis a high performance ZnCo₂O₄ nanowire array and a novel ZnCo₂O₄ nanosheet array structure which woven from nanowires directly grown on NF.At the same time,a high specific capacitance ZnCo₂O₄@Ni?OH?₂ composite electrode material was synthesized by a simple hydrothermal method.The composite material has the advantages of high specific surface area,faster redox rate and various pore structure.The main research results obtained in this paper are as follows:?1?The ZnCo₂O₄ nanowires?ZnCo₂O₄ NWAs?and ZnCo₂O₄ nanosheet arrays?ZnCo₂O₄ NSAs?grown on the nickel foam were synthesized by mild hydrothermal method and high temperature calcination method with changing the experimental solvent.The two materials were prepared as electrodes and tested in series in a three-electrode system with 2 M KOH as the electrolyte.The electrochemical properties of the two electrodes were characterized by a series of tests.At a current density of 2 mA cm^-2,the specific capacitance of the ZnCo₂O₄ nanowire electrode is as high as 2049 F g^-1,which was 1.8 times higher than that of the ZnCo₂O₄ nanosheet electrode at the same current density.The ZnCo₂O₄ nanowires also performed well in terms of cycle stability,after 3000 cycles,its capacitance retention rate was 88.8%,which was higher than that of ZnCo₂O₄ nanosheets?79.9%?.The electrochemical properties of ZnCo₂O₄nanowire are higher than those of many reported ZnCo₂O₄ electrode materials.The ZnCo₂O₄ NWAs//AC asymmetric supercapacitors?ASC?was assembled with ZnCo₂O₄NWAs as positive electrode and its electrochemical performance was tested.The results show that the energy density of the ASC is 37.5 W h kg^-1(358.2 W kg^-1),and the capacitance loss is 11.8%after 3000 cycles of the current density of 10 mA cm^-2.This result is superior to the electrochemical propoties of other reported ASCs.?2?The composite ZnCo₂O₄@Ni?OH?₂ core-shell nanostructured electrode material was synthesized on the Ni foam by two-step hydrothermal method and controlled reaction time.The specific properties of the sample are characterized by the structure,morphology and electrochemical methods.Under the current density of 2 mA cm^-2,the mass ratio capacitance of ZnCo₂O₄@Ni?OH?₂ measured by the standard three-electrode system reached 2718.49 F g^-1,and its area specific capacitance was 6.47 F cm^-2.The specific capacitance retained 73.3%of its initial capacitance after 3000 cycles of 20 mA cm^-2 high current dencity.The electrochemical performance of the composite electrode is better than that of many reported composite electrode materials.The ZnCo₂O₄@Ni?OH?₂//AC ASC was assembled using synthesized ZnCo₂O₄@Ni?OH?₂and AC as positive and negative electrodes,respectively.The maximum energy density of the ASC device reached 46.6 W h kg^-1(283.4 W kg^-1).and the capacitance loss rate was 9.7%after 3000 cycles.The properties of this ASC are also better than the electrochemical properties of many reported ASC.Those results indicate the good electrochemical performance of the ZnCo₂O₄@Ni?OH?₂ electrode,which can be applied to the field of energy storage devices such as supercapacitors.