Preparation Of Nanostructured Cobalt(â…¡, â…¢) Oxide And Their Electrochemical And CO Catalytic Oxidation Performances

Cobalt (II, III) oxide stands as an important p-type functional material with applications in lithium ion batteries (LIBs), heterogeneous catalysts, gas sensors, electrochromic devices, field emission, optical and magnetic materials. The present dissertation aims to develop a facile and novel method to realize the synthesis of cobalt oxide arrays grown directly on the large-scale metallic substrates to enhance the initial coulombic efficiency efficiency and cycling performance when they are used directly as anode materials for LIBs. Moreover, the results of exposing planes and apparent activation energy of CO oxidation over the CO3O4show the importance of morphology in the the performance of catalysts. The main contents and results include the following:(1) It is the first time to report the rhombus-shaped CO3O4NR arrays grown directly on nickel foil via fluorine-mediated hydrothermal synthesis. The effects of synthetic conditions of the fluorine-mediated hydrothermal synthesis including the time, substrate, NH4F, halogen types, temperature and cobalt source, etc. on the morphology, size, structure, array density and mechanical adhesion on nickel foil of the rhombic nanorods have been investigated in detail. The possible formation mechanism of the novel NR arrays was investigated by XRD, Raman spectroscopy, SEM, TEM and XPS.(2) We study the electrochemical and CO catalytic oxidation performances of rhombus-shaped CO3O4NR arrays on nickel as LIB anode electrode without any ancillary materials. The arrays exhibit relative a high coulombic efficiency of80.7%and a high reversible capacity of1000mAh g-1over20cycles at a current rate of1C. Moreover, we explore the possible reaction mechanism and inactive reasons for CO oxidation performances of CO3O4catalyst based on the analysis of exposing surface plane and apparent activation energy on the rhombic CO3O4nanorod.(3) Novel CoO nanostructure arrays on nickel foam with needle-like and rhombic morphologies have been prepared by using urea and hexamethylenetetramine as hydrolysis agents through fluoride-assisted hydrothermal method, respectively. The possible formation mechanism and effect factors of the novel arrays were systematically investigated by X-ray diffraction, scanning and transmission electron microscopies, and fourier transform infrared spectroscopy. We discover carbonate anions can act as a structure directing agent in dissolution-recrystallization process and the affinity to Co2+of different anions are found in the order of CO32-> F-> OH-.(4) We study the electrochemical performance of different one-dimensional CoO nanoarray morphologies on electrochemical properties. Higher initial coulombic efficiency and first discharge capacity of needle-like CoO arrays can be mainly attributed to the larger specific surface area. For the rhombic NR arrays, although the initial coulombic efficiency and first discharge capacity are lower, the cycle performance is much better than needle-like CoO arrays. Rhombic CoO arrays can deliver initial coulombic efficiency of61.8%and initial discharge capacities of1447.9mAh g"1. In addition, they also maintain high reversible capacities of719mAh g"1at0.2C after50cycles, which is62.4%of the second cycle.