Optimizing Co Nanoflakes Growth Parameters and Modifying Their Electro-catalytic Performance Using Carbon Nanostructures for Water Oxidation Reaction

Pourreza, Mohammad | 2016

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 49393 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Naseri, Naimeh
  7. Abstract:
  8. Ease of solar hydrogen production using water splitting and its environmental benefits, distinct hydrogen from other energy carriers. Hydrogen is the most abundant material in the world that make up more than 90% of the world compounds. So applying this material as a clean fuel is the best way to prevent environmental problems caused by fossil fuels. For efficient hydrogen production from water, a suitable electrocatalyst with low overpotential, high mechanical strength and reasonable catalytic activity must be utilized. In this research, cobalt based electrocatalyst was used considering that electrodepositon conditions play an important role in its final efficiency. On the other hand, using carbonaceous support layers including nanomaterials such as graphene and carbon nanotubes, can reduce overpotential and increase efficiency of the electrocatalyst. In this regard, the optimum graphene to carbon nanotubes mass ratio is an open question which will be investigated in this research. For this purpose, current densities from 0.2 mA/〖cm〗^2 to 20 mA/〖cm〗^2 with 2000s to 2h duration times examined. At first, the best time of deposition were find following with studying several current densities. In high current densities, due to suddenly move of cobalt particles to steel-mesh substrate conditions, for orderly growth of cobalt nanoflakes was not available and density of nanoflakes was very low. Cobalt nanoflakes were not formed at low current densities but at medium current density 7 mA/〖cm〗^2 , aspect ratio and density of cobalt nanoflakes were highest and hence, this condition was selected as the optimum one. Finally, a carbon based paste containing different ratios of graphene oxide to carbon nanotubes, made used as a mediator layer to increase conductivity of substrate. The best method to reduce graphene oxide was found. At this step, it was determined that the sample with 50% of graphene oxide with continuous electrochemically reduction method had lowest overpotential ( 289 mV ) and
  9. Keywords:
  10. Carbon Nanotubes ; Nanoflakes ; Graphene Sheet ; Graphene Oxide ; Cobalt Nanoflakes ; Overpotential

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