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Synthesis, Characterization, and Investigation of the Electrocatalytic Performance of the Earth-Abundant Transition-Metal-Based Compounds Toward Alkaline Oxygen Evolution Reaction

Karami, Milad | 2024

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 57399 (03)
  4. University: Sharif University of Technology
  5. Department: Chemistry
  6. Advisor(s): Taherinia, Davood
  7. Abstract:
  8. Hydrogen gas was introduced as a fuel with high energy density and environmentally friendly, and the electrolysis of water is one of the widely used methods to produce this gas. In order to reduce the energy required for this process, the introduction of electrocatalysts with high activity and stable is on the agenda. In this research, the electrocatalytic performance of a composite of MgCo2O4 and Ni3S2 on a nickel foam substrate was investigated in order to produce oxygen in an alkaline environment. To prepare MgCo2O4 compound, hydrothermal method and Ni3S2 compound, electrochemical deposition method with the help of cyclic voltammetry technique was used. According to the results of XRD analysis, the crystal structures of the synthesized materials were in accordance with the standard patterns. FESEM analysis showed the morphology of the composite as nanosheets with a thickness of 70 nm. Also, the EDS spectrum confirmed the presence of all elements and the elemental mapping showed a uniform distribution of elements. In order to investigate the effect of cycle number on the electrochemical performance of the final compound, Ni3S2 compound was synthesized with the number of cycles 1, 4, 7 and 10. Finally, it was observed that MgCo2O4 @ Ni3S2 composite synthesized during 7 cycles has better performance in oxygen evolution reaction (OER). This composite required an overpotential of 280 mV to perform the oxygen production reaction in 1 M KOH solution and achieve a current density of 50 mA cm-2, respectively, and the Tafel slope was equal to 183.9 mV dec-1. Also, this composite showed good stability in the oxygen evolution reaction. In a way that at a potential of 1.5 V vs. RHE, the current density decreased by only about 6% during 10 hours. In addition, the investigation of the electrochemical active surface area (ECSA) of the composites was carried out through the cyclic voltammetry technique and the comparison of the charge transfer kinetics between these composites and the calculation of the equivalent circuit with the help of electrochemical impedance spectroscopy (EIS) that again the 7-cycle composite has more active surface and kinetics showed easier charge transfer. In addition, the performance of these compounds in the hydrogen evolution reaction (HER) was also investigated under the same conditions as previously, the 7-cycle composite with an overpotential of 330 mV at a current density of 50 mA cm-2 and a Tafel slope of mV dec-1 186.1 showed better performance than other composites. Electrochemical impedance spectroscopy was also performed and the equivalent circuit was calculated by fitting the data. Finally, this composite showed an acceptable performance in the overall water splitting reaction
  9. Keywords:
  10. Electrocatalysts ; Compounds Based on Transition Metals ; Water Electrolysis ; Water Splitting ; Overall Water Splitting ; Oxygen Production

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