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Electrochemical Preparation and Study of Transitional Metal Mixed Oxides as Supercapacitor Electrodes

Jafarzadeh, Sanaz | 2013

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 44528 (03)
  4. University: Sharif University of Technology
  5. Department: Chemistry
  6. Advisor(s): Gobal, Fereydoon
  7. Abstract:
  8. In this thesis, the improving effects of deposited metal oxides onto or next to each other and the advantages of every metal oxide were considered. In the next step, the substrate improvement was studied and the porous metal oxides with ideal supercapacitive properties with porosity increase of substrate were obtained.CoFeO2 supercapacitor was prepared by chronoamperometric ethod.CoFeO2waselectrodeposited at room temperature and presents wide potential window and good capacitive properties in comparison with other metal oxides.Layers of cobalt and manganese oxides were co-deposited or deposited on top of each other or next to each other by chronometric method onto stainless steel substrate. Deposition potentials of 1 and -1 V for the anodic and cathodic depositions were employed. Specific capacitance values in the range of 38.5 to 78 F g-1 were found with cobalt oxide on top of manganese oxide having the lowest and manganese oxide on top of cobalt oxide having the highest capacitances. The usefulness of the electrodes was characterized by cyclic voltammetry (CV), charge-discharge cycling, and electrochemical impedance spectroscopy (EIS) in 2M NaOH electrolyte for redox supercapacitor applications. The latter presented the best charge/discharge behavior with no voltage drop due to lower ohmic resistance in prepared substrate; although the steadiest current observed in the course of voltammetry was due to the former. The evaluated double layer and specific capacitances for co-deposited sample according to the impedance studies were 1.75 and 47.5 F g-1, respectively being in good agreement with voltammetric measurements. A porous nickel (P-Ni) substrate was prepared by selective leaching of zinc from pressed pellets containing powders of Ni & Zn in 4 M NaOH solution. Anodic deposition of manganese oxide onto the porous Ni substrate (MnOx/P-Ni) formed nano-flakes of manganese oxide layers as revealed in SEM studies. Pseudocapacitance of this oxide electrode was evaluated by cyclic voltammetry (CV) and chronopotentiometry (CHP) in 2 M NaOH solution. The specific capacitance of the Mn oxide electrode was as high as 1515 F g−1, which was ten times higher than Mn oxide deposited on a flat Ni-ribbon. 80% of capacity was retained after 200 charge/discharge cycles. The pseudocapacitance and morphology of electrodeposited transition metal oxides depend significantly on the morphology of the substrate. The nano-porous Ni substrate, derived from selective electro-dissolution of antimony from an electro-deposited Ni–Sb alloy, effectively promotes the electrochemical utilization of deposited manganese oxide. The large electronic and ionic conduction within the nano-structured deposit improve the energy storage performance of Mn oxide as compared to that on flat Ni substrate. In this work, the MnO2 specific capacitances of around 612 F g-1 were obtained, which was five times higher than Mn oxide deposited on a flat Ni-ribbon
  9. Keywords:
  10. Supercapacitor ; Manganese Oxide ; Cobalt-Manganes Oxides ; Layered Oxides ; Potentionstatic Deposition ; Specific Capacitance ; Porous Nickel Substrate ; Nanoflakes

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