Electrodeposition Of Cobalt/Nickel Hydroxide And Oxide And Their Electrochemical Capacitive Properties

At present, electrochemical capacitor is one kind of important new energystorage equipment, which between conventional capacitors and battery. Electrode isan important component of electrochemical capacitor, and the electrode material is animportant part of building electrode. Therefor, the research and preparation ofelectrode materials with good electrochemical performance plays a vital role in thedevelopment of electrochemical capacitor. Cobalt/Nickel hydroxide and oxide have apotential application in the electrode materials of electrochemical capacitor due totheir excellent electrochemical properties resulting from the good redox reactionactivity and unique structure.The present work reviewed the electrochemical capacitors and their electrodematerials, and then prepared the four kinds of electrode materials by electrodepositiontechnique. Their morphologies, crystal structure and components were characterizedby means of modern analysis techniques. The capacitive behaviors of the resultantmaterials were also measured by electrochemical skills. The main content is asfollows:1. Nickel hydroxide film was prepared by electrodeposition on nickel foil inNi(NO₃)₂ aqueous solution for the electrode materials of electrochemical capacitors.The structure and morphology of products were characterized using X ray diffraction(XRD) and field emission scanning electron microscopy (FESEM), respectively. Theexperimental results of XRD show that the products are typicalα-phase nickelhydroxide. The FESEM results reveal that the as-preparedα-Ni(OH)₂ displays aloosely packed structure assembled by the relatively bigger particles (90 nm). Thefurther observations indicate that the big particles are composed of several smallnanoparticals (30-40 nm). The component and thermal stability of the products arerespectively measured by FT-IR, thermogravimetry and differential thermal analysis(TG/DTA). The electrochemical performances are investigated by cyclic voltammetry(CV) and galvanostatic charge-discharge technique in 1 mol·L^-1 KOH electrolyte. Theresults show that the product has excellent electrochemical performances and itsspecific capacitance value as single electrode is up to 2520 F·g^-1. Furthermore, the effect of deposition conditions such as deposition potential and concentration ofNi(NO₃)₂ solution on the electrochemical capacitance of the deposited Ni(OH)₂ filmsis discussed in detail.2. Nickel oxide thin film is prepared by thermally treating the above-mentionedNi(OH)₂ film at different temperature in air. The crystal structure and surfacemorphology of the thin film is characterized by X-ray diffraction (XRD) and fieldemission scanning electron microscopy (FESEM), respectively. The electrochemicalperformance of the thin film electrode is also investigated using cyclic voltammetry,galvanostatic charge-discharge, and electrochemical impedance spectroscopy. NiOthin film, which is prepared by electrodeposition under the conditions of Ni(NO3)2solution concentration of 0.08 mol·L^-1 and potential of -0.9 V, and then thermallytreated at 250℃, is a typical cubic structure. The electrochemical test results show ithas good electrochemical performance. The single-electrode specific capacitancevalue is up to 1220 F·g^-1, and expected to as a promising electrode material ofelectrochemical capacitors.3. Cobalt hydroxide film was electrodeposited on nickel foil in Co(NO₃)₂aqueous solution. The structure and morphology of Co(OH)2 film were characterizedusing X-ray diffraction (XRD) and field emission scanning electron microscopy(FESEM), respectively. The component and thermal stability of the sample weremeasured by FT-IR and thermal analyses, including thermogravimetry (TG) anddifferential thermal analysis (DTA). The electrochemical performance wasinvestigated by cyclic voltammetry, constant current charge/discharge technique andelectrochemical impedance spectroscopy. Furthermore, the effects of the appliedpotential and the total electrical quantity during electrodeposition of cobalt hydroxidefilm on its specific capacitance were studied. The results show that the as-preparedmaterials areβ-Co(OH)2 with a uniform sheet-like network morphology and haveexcellent electrochemical performances. The specific capacitance as single electrodeis up to 1042 F·g^-1, and remains at about 72% of the initial value after 500 cycles at acurrent density of 10 A·g–1. So it is a promising electrode material for electrochemicalcapacitors.4. The Co3O4 film was prepared by thermally treating the above-mentioned Co(OH)₂ film at different temperature in air. The structure and morphology of theCo3O4 film were characterized using X-ray diffraction (XRD) and field emissionscanning electron microscopy (FESEM), respectively. The electrochemical propertieswere also investigated using cyclic voltammetry and galvanostatic charge-discharge.Co₃O₄ thin film, which was prepared by electrodeposition under the conditions ofCo(NO₃)₂ solution concentration of 0.05 mol·L^-1 and potential of -1.0 V, andsubsequent thermally treated at 250℃, is a typical spinel structure. Theelectrochemical test results show it has good electrochemical performance, the singleelectrode specific capacitance value is up to 413 F·g^-1 and showing good cyclestability, expected to as a promising electrochemical capacitors electrode material.