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Synthesis and Characterization of TiO2 and WO3 Thin Film Photoanodes Containing Noble Metal Nanoparticles and (TiO2)x-(ZnO)1-x Nanocomposite Photanodes for H2 Production

Naseri Taheri, Naimeh | 2011

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 42326 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Moshfegh, Ali Reza
  7. Abstract:
  8. Growing demand on energy and limitation and consequence of fossil fuels have caused to utilize the clean and renewable energy sources. Hydrogen is a clean energy carrier which produced just water vapor during combustion. Today, methods which are usually used to produce this fuel are based on using fossil fuel compounds. Therefore, utilizing new production methods is unavoidable. One of these methods is using semiconductors such as TiO2 to spilt water and produce H2 by solar irradiation. Reducing the energy gap of these semiconductors to match the solar spectrum, specially in its visible range, modification of their structures, surfaces and stability are the main challenges in hydrogen production processes.In this research, TiO2 thin films containing different concentrations of Au and Ag nanoparticles using chemical sol-gel method have been synthesize and used as photoanode in the photoelectrochemical cell to produce hydrogen from water. Physical and photoelectrochemical characterization of Au:TiO2 thin films revealed formation of Au nanoparticles in the nanocrystalline TiO2 film. Reduction of bang gap energy and enhancement of electrical conduction by increasing the gold content in the layers and also coverage of TiO2 surface in high Au concentrations has caused that layer with 5 mol% Au shows the highest photosensitivity and hydrogen production yield. This optimum concentration for Ag:TiO2 system is determined at 1 mol% due to accumulation of Ag nanoparticles on the surface and their existence in ionic state. For Ag:WO3 and Au:WO3 nanocomposite thin film photoanode a similar mechanism and behavior has been observed with an optimum concentration at 2 and 1 mol% respectively. The highest amount of H2 is produced in water splitting reaction for Au:TiO2, Ag:TiO2 systems in basic solution and Au:WO3 and Ag:WO3 systems in acidic electrolyte were obtained about 2.8, 193.2, 2.1 and 2.2 μmol/h, respectively. Moreover, Studying photoelectrochemical performance of (TiO2)x-(ZnO)1-x nanocomposite photoanodes in basic electrolyte revealed that applying strong anodic polarization on these layers resulted in band gap reduction, increase of effective surface area and improvement of charge transport. By repeating this experiment, photoelectrochemical efficiency of this system increased 100 times more than before anodization
  9. Keywords:
  10. Metallic Nanoparticles ; Titanium Dioxide ; Tungsten Oxide ; Hydrogen Producing ; Photoelectrochemical Cell ; Water Splitting

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