The Investigation On The Fabrication And Electrochemical Properties Of Ternary Metallic Oxides

In the past few decades, people mainly focused on the research of binary metallic oxides instead of ternary metallic oxide. Nowadays, ternary oxide nanocrystals were recently considered as outstanding building blocks for optoelectronic and electrochemical device applications due to their inherent properties, such as wide bandgap, high dielectric constant and active ability of electron transportation. For an example, tunability of valance states in ternary metal oxides usually ensures high electric conductivity and rich electrochemical active sites. Similar crystal structure and ion radii also make it possible for the component adjusting to meet the bandgap requirements of optoelectronic application. Particularly, supercapacitors has sprung up owing to high power density, rapid charging/discharging characteristics and execllent cycle stability. The key to improve the electrochemical performance of supercapacitor is the choice of active electrode material. Most binary metal oxides such as MnO2, CoO, CO3O4, NiO are wide bandgap semiconductor or even insulation materials, which conductivity and cycle stability were poor, or materials with good performance such as RUO2 are expensive and toxic. NiCo204 has gained more and more interest due to better conductivity, larger specific surface area and lower toxicity. Up to now, numerous approaches have been employed to synthesize ternary oxides, including physical and chemical methods. However, apart from lacking of a universal method, adscititious chemicals and post treatment are usually needed in these methods, as well as exacting requirements such as high temperature and pressure, causing inevitable environmental issues and cockamamie steps. This paper developed two different methods to synthesize ternary oxide with different structure and morphology, one is traditional template method which used to synthesis single and double NiCo₂O₄ nanosphere, and was applied in supercapacitor; another is a universal laser-hydrothermal synthesis of various ternary oxide nanocrystals for high-performances photodetectors and pseudocapacitor through combining laser ablation in liquid （LAL） and short-time hydrothermal growth. The concrete research content is as follows:（1）The single-shell and double-shell spheres were fabricated via one-cycle and two-cycle coating of the NiCo₂（OH）₆ intermediate material on carbon sphere templates, respectively. The specific surface area of NiCo₂O₄ hollow spheres, was enlarged 50% (from 76.6 to 115.2 m2 g^-1) when their structure was transformed from single-shell to double-shell.（2）To investigate the electrical properties of the samples treated under different annealing temperature and atmosphere,AC impedance measurements were carried out.It demonstrated that the low-temperature hydrogenation greatly decreased both the internal resistance and the Warburg impedance. Consequently, a specific capacitance increase of more than 62%, from 445 to 718 F g^-1, was achieved at a current density of 1.Under the current density of A g"1 and over 80% capacitance can still be retained after 2000 cycles. In order to study the full cell electrochemical performance, we fabricated NiCo₂O₄/AC asymmetric supercapacitor with the sample of low-temperature,under the current density of 50 mA cm-2 and 89.9% capacitance can still be retained after 2000 cycles.（3）This approach combines laser ablation in liquid with short time hydrothermal treating and oxides including Zn₂GeO₄, NiCo₂O₄, Zn₂Sn_O4, ZnFe₂O₄, ZnMnO₃, and Fe₂GeO₄ are synthesized in normal pressure and temperature. The detailed reaction process and mechanism are investigated based on the synthesis of Zn₂GeO₄ nanorods that the whole reaction includes following steps:instant and simultaneous nucleation and growth, etching and diffusion growth and consequent growth. Single crystalline Zn₂GeO₄ nanorods formed within 1 h and Ge based composites can be obtained under ambient environment. Electrochemical capacitor based on NiCo₂O₄ nanocrystals exhibits excellent capacitive performance that specific capacitance of 1113 F g^-1 at a current density of 1 A g^-1 is obtained and 68.7% of its initial capacitance is remained at a high current density of 20 A g^-1.