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Enhancement of Optical Absorption and Water Oxidation Reaction in One Dimensional Nanostructured Hematite Photoanodes

Fathabadi, Milad | 2021

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 53722 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Naseri, Naimeh
  7. Abstract:
  8. Hydrogen is known to be a renewable and clean source of energy, which produces water vapor and zero carbon dioxide as a result of its combustion. Photoelectrochemical water splitting (PEC) could be a promising approach in order to generate hydrogen by sunlight. Hematite (α-Fe2O3), as the most abundant naturally occurring form of iron oxide with suitable band gap, low cost, high stability and nontoxicity is considered to be an ideal photoanode. However, intrinsic drawbacks of hematite including low electrical conductivity, limited hole diffusion length, and high recombination rate of electron-hole pairs restrict its photoelectrochemical performance efficiency. In the present research, titanium-doped hematite nanostructured photoanodes are synthesized via a low cost and facile hydrothermal method. Furthermore, the hydrothermal challenges regarding simultaneous control on both morphology and effective doping are investigated, and the average photocurrent density is improved from 0.22 mA/cm2 to 1.23 mA/cm2 at 0.5 V vs. Ag/AgCl by means of the new optimized method and reducing the synthesis procedure errors, and the conventional hydrothermal fabrication method of hematite nanostructures is shown to suffer lack of complete reproducibility. In addition, a novel electrochemical approach to enhance the photoelectrochemical performance of hematite nanostructures is introduced, its optimization is discussed and it is indicated that single cycle cyclic voltammetry at 5 mV/s scan rate at optimum potential window would enhance the photocurrent density by a factor of 1.5 on average. As an example, for one of the optimized 1% Ti:Fe2O3 samples, the photocurrent density increases from 1.71 mA/cm2 to 2.55 mA/cm2 at 0.5 V vs. Ag/AgCl upon activation treatment. The photoanode stability is also evaluated, which is sustained for 6 h by performing activation treatment once after each photoelectrochemical splitting hour. Activation effect is also studied by electrochemical and structural characterizations, which suggest that the activation treatment not only exhibits electrocatalytic effect, but also facilitates charge carrier transport through the bulk of hematite by increasing the number of charge carriers. Meanwhile, it enhances the crystallinity of nanostructured hematite
  9. Keywords:
  10. Hematite ; Hydrogen Producing ; Electrochemical Treatment ; Water Splitting ; Iron Oxide ; Photoelectrochemical Water Splitting ; Electrochemical Activation

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