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Investigating the Electrochemical Behavior of Co-Zn Sulfides and Hydroxides on Copper Oxide Nano-structures Grown on Copper Foam for Application in Electrochemical Supercapacitors

Shahi, Mahdiyeh | 2021

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 53685 (03)
  4. University: Sharif University of Technology
  5. Department: Chemistry
  6. Advisor(s): Shahrokhian, Saeed
  7. Abstract:
  8. In the first part, Co-Zn hydroxides were deposited onto CuO nanorods, and their electrochemical behavior and capacitive performance were investigated. To this end, Cu(OH)2 nanorods were grown on copper foam through a chemical process. Then, Cu(OH)2 were converted to CuO nanorods via a calcination process. In the next step, Co-Zn-OH sheets were electrodeposited on CuO nanorods. FE-SEM images of the prepared electrodes demonstrate the formation of Co-Zn-OH nanosheets onto CuO nanorods. Crucial electrochemical evaluations such as cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), rate capability, and electrochemical impedance spectroscopy (EIS) were carried out. According to the galvanostat charge/discharge evaluations, the prepared electrodes rendered areal capacity of 253.3 mC.cm-2 at 3 mA.cm-2 in an alkaline electrolyte. Cyclic stability of the electrode was investigated through 1000 GCD cycles. According to the obtained results, the electrode retained 95% of its initial capacity after 1000 cycles. The EIS results showed an appropriate equivalent series resistance (ESR) of 1.05 Ω. The presence of nanostructures layered double hydroxides (LDHs) of Co and Znfacilitates ion transfers and enhance the specific surface area, which resulted in the improved capacitive performance. Iron sulfide structures were electrodeposited graphene oxide coated nickel foam as the negative electrode for assembling asymmetric supercapacitor. Finally, the asymmetric supercapacitor represented areal capacity of 19.6 mC.cm-2 at 1.4 mA.cm-2. The maximum of energy and power densities of 11.47 mWh.cm-2 and 3.03 W.cm-2 were achieved. In the second part, Co-Zn sulfides were electrodeposited onto CuO nanorods. Initially, the Cu(OH)2 nanorods were chemically grown on copper foam and converted to CuO through a calcination process. Afterwards, the Co-Zn-S were electrodeposited onto CuO nanorods, forming core/shell structures. The electrochemical measurements (e.g. CV, GCD, EIS, rate capability, and life stability) and characterization techniques (e.g. XPS, XRD, and Raman) were carried out. The Co-Zn-S represented the areal capacity of 538.4 mC.cm-2 at 3 mA.cm-2, which showed an enhancement of about 7.86 times in capacity compared to CuO substrate. The obtained results demonstrated that the presence of Co-Zn-S electroactive materials onto CuO resulted in the enhancement of pseudocapacitive behavior of the prepared electrodes. The cycle stability f the electrode were evaluated after 4500 GCD cycles, showing 113% retention. Finally, the assembled Co-Zn-S@CuO-CF//Fe-S/GO-NF asymmetric supercapacitor represented specific capacity of 82.3 C.g-1 at 0.52 A.g-1. The maximum energy and power densities of the asymmetric supercapacitor were 25.7 wh.kg-1 and 8.73 kW.kg-1
  9. Keywords:
  10. Supercapacitor ; Layered Double Hydroxide (LDH) ; Pseudocapacitor ; Transition Metal Sulfide ; Cobalt-Zinc Hysroxide ; Cobalt-Zinc Sulfide ; Metal Foam

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