Metal Oxide Ordered Electrode Material And Capacitance Performance Study

Electrochemical capacitor is a novel energy storge system due to fast charge-discharge rate,long cycle life and others.Energy density and cycle life of electrochemical capacitors are the main factors affecting their electrochemical properties.The energy density of electrochemical capacitors is determined by both specific capacitance and operating voltage window.Limited by the decomposition voltage of water,the increasing specific capacitance becomes the mostimportant method to improve the energy density of electrochemical capacitors in the aqueous electrolyte system.This dissertation focused on synthesis of ordered electrode materials and researches on electrochemical reaction process and mechanism.Redox components were also used in electrolyte and in electrode to improve the specific capacitance,energy density and cyclic life of supercapacitors.The composite electrode materials with Zn4(OH)6CO3·H2O(Hydroxide zinc carbonate,HZC)as the main component were synthesized by hydrothermal method.The particles presented regular hexagonal sheets morphology and self-assembled to a three-dimensional ordered array on the surface of foam Ni.The HZC electrodes showed typical pseudocapacitive behavior.REDOX process of Zn(II)was completed with aid of insertion and release of electrolyte solution ions on the electrode surface and between layers in KOH system.Subsequently,an effort was taken to improve the specific capacitance in KOH electrolyte by redox additives.The electrochemical reaction on the surface of HZC electrode conforms to the "Electron Shuttle" mechanism in KOH+K3[Fe(CN)6].[Fe(CN)6]3-promoted electron transfer and improved the capacitance performance of the electrode through participation and synergism.S2O82-participated in the oxidation process of Zn(II)and improved the specific capacitance of the electrode.Finally,redox active components were further introduced into the electrode phase.Mo doped HZC materials on foam Ni were prepared.MoO42-inserted into interlayer by replacement or intercalation.Electrostatic attraction between the layers and ions between the layers was increased.Zn(Ⅱ)was partial replaced by Al(Ⅲ)at the same time.MO42-in the interlayer provided additional capacity in the process of electrode reaction and promotd electron transfer.Electrostatic attraction between layers stablized MoO42-during long cycle test and improved Mo-HZC stability eventually.