Preparation And Electrochemical Characterization Of Metal Oxide Electrode Materials

Supercapacitor is a new kind of energy storage device that between chemical battery and traditional capacitor. They can be used either by themselves as the primary power or in combination with batteries or fuel cells. Because supercapacitor have advantages of high power densities and very long cycle life, it have drawn more and more attention in recent years. The research work of supercapacitor mainly focuses on the electrode material. Due to their high specific capacitance and low manufacturing cost, NiO and MnO2 become the focus in electrode material. More recently, graphene is also used by researchers as ideal supercapacitor electrode material for research with its theoretical specific surface area of 2630m2/g. Also, its chemical stability, high electrical and thermal conductivity, and mechanical strength and flexibility are attractive as conformal electrode materials particularly for flexible supercapacitor.In this thesis, we have investigated the electrode materials preparation and capacitive property. The main content is as follows:1. Ni（OH）₂ thin film was simply fabricated on nickel foam substrate by direct current electrodeposition from aqueous solution of Ni（NO3）2. NiO film on nickel foam（NF） with porous and 3D superstructures is prepared by electrodeposition of Ni（OH）2 and followed by heat-treatment in air. The as-prepared porous NiO/NF electrode shows ultrahigh capacitance between the potential range of-0.1–0.5 V, and a maximum specific capacitance as high as 2393 F/g can be achieved at a high charge/discharge current density of 40 A/g, and it remains for 70% when the current density increases to 100 A g-1. This work illustrates a promising platform for other electrode materials to reap high capacitance and high rate capability for supercapacitor applications.2. MnO₂/NF electrode obtained by MnO₂ film electrodeposited on nickel foam（NF） from aqueous solution of MnSO2. The morphology and composition of the electrodeposited layer coated on nickle network were characterized by FESEM and XRD. Galvanostatic charge/discharge measurements reveal that the MnO2/NF electrode has excellent electrochemical capacitance between potential range of-0.1–0.9 V, and a maximum specific capacitance as high as 1061 F/g could be achieved in Na2SO4（0.5 mol L-1） solution at a charge/discharge current density of 5 A/g.3. Graphene hydrogel/nickel foam（GH/NF） composite electrode, which is achieved by hydrothermally assembling graphene hydrogel（GH） on nickel foam（NF）. The three-dimensional structure of GH prevents the aggregation of graphene, while the NF enhances the conductivity of the active material. The as-prepared GH/NF electrode shows standard electric double-layer capacitive behavior and high capacitance between the potential range of-1⁰ V, and a maximum specific capacitance as high as 180 F/g can be achieved at a charge/discharge current density of 1 A/g, and it remains for 90% when the current density increases to 5 A/g.4. Ni（OH）₂ film electrodeposited on as-prepared GH/NF electrode from aqueous solution of Ni（NO3）2, The morphology and composition of the electrodeposited layer coated on nickle network were characterized by FESEM and XRD. Galvanostatic charge/discharge measurements reveal that the Ni（OH）2/GH/NF electrode has excellent electrochemical capacitance between potential range of 0-0.45 V, and a maximum specific capacitance as high as 2888 F/g could be achieved in KOH（3 wt%） solution at a charge/discharge current density of 5 A/g. The repetitive charge/discharge shows that after 800 times cycles the specific capacitance reduce to 64%, it has good electrochemical stability.