Synthesization And Pseudocapacitive Performance Of Cobalt-Based Compound Nanorod Arrays

Though metal compounds (metal oxides/sulfides/hydroxides) electrodes lead to high energy density, in normal cases, the chargh-discharge rate is high, especially when the loading of active material is high, the power density is largerly sacrificed as the result of their poor electrical conductivity. Due to the physio-chemical changes (the changes in structure and the irreversible products) during long time Faradaic reactions, the cycling performance of those electrodes can not reach such a high level. In order to solve the problems of that low loading of the active materials and poor stability of the electrodes simultaneously, we design the core-shell structure with the charge-diffusion-favoured structures, such as nanoflakes, mesoporous or hollow structures, etc. as shell, and the hierarchical nanorod arrays with modified electrical conductivity as core, which not only increases the loading of the active materials and decreases the "inert materials", but also enhances the stability of the electrode materials during long time of Faradaic reactions. The main contents of thesis are as follwing:1) The precursor nanorod arrays were prepared by hydrothermal method, and the hierarchical Cu0.27Co2.73O4 nanorod arrays were successfully synthesized after annealing treatment. We characterized their structures and tested their electrochemical performances, and explored the potential application of Cu0.27Co2.73O4 for electrochemical capacitors (ECs). Copper irons were incorporated into the lattice of Co3O4 and formed hierarchical Cu0.27Co2.73O4 nanorod arrays. It is shown that the nanorod is composed of Cu0.27Co2.73O4 nanoparticles. The porous structure, and the inter-space between adjacent Cu0.27Co2.73O4 rods are benefitful for the effective penetration of the electrolyte, reduction of the charge transfer resistance and enhancement of the utilization for active materials. The voltage window increases to 0.55 V (from 0 to 0.55 V) with a lower voltage drop in charge-discharge curves, and the rate of rise is 22% compared to Co3O4 synthesized in the same condition, which is attributed to copper incoporation. The areal capacitance (Ca) of Cu0.27Co2.73O4 at 8.8 mA·cm-2 maintains nearly 2 F·cm-2 after 3000 cycles.2) In order to obtain Cu0.27Co2.73O4/MnO2 hybrid arrays, we adopted the carbon modification method. We characterized their structures and electrochemical performances, and explored the potential application of Cu0.27Co2.73O4/MnO2 for ECs. The synergistic effect between hierarchical MnO2 layer composoed of MnO2 nanoflakes and Cu0.27Co2.73O4 nanorods:enhancing the effective utilization of active materials, fast transportation and penetration for electrons and ions, lowering the electrochemical impendence, and maintaining the structural integrity during long-term redox chemical reaction. Ca of Cu0.27Co2.73O4/MnO2 at 18.6 mA·cm-2 is maintained nearly at 4 F·cm-2 after 3000 cycles, the increase rate of Ca is double compared to that of Cu0.27Co2.73O4, and the stability, durability of the cycle performance for Cu0.27Co2.73O4/MnO2 are much better than those of Cu0.27Co2.73O4.3) We synthesized Co9S8 nanorod arrays through in situ chemical reaction method, we choose Co9S8 nanorod arrays as template to obtain the initial thin MnO2 layer as the result of the reaction between KMnO4 and Co9S8. Then the growth of MnO2 takes place on base of the initial MnO2 layer through hydrothermal reaction process. We characterized their structures and electrochemical performances, and explored the potential application of Co9S8/MnO2 for ECs. Co9S8 exhibits good redox behavior and excellent electrocatalytic activity. Hierarchical MnO2 layer composed of MnO2 nanoflakes attached to porous Co9S8 nanorods not only guarantees the fast transportation and penetration for electrons and ions into the core region, lowering the electrochemical impendence, enhancing the effective utilization of active materials, but the initial thin MnO2 layer also serves as a protective layer to enhanced bonding between Co9S8 and MnO2, maintaining the structural integrity during long-term redox chemical reaction. The specific capacitance of Co9S8/MnO2 can be maintained nearly 1100 F·g-1 after 5000 cycles. The stability and durability of cycle performance remain well.