Loading...

Synthesis and Investigation on Physical and Photoelectrochemical Properties of Visible Active TiO2/Graphene Based Nanocomposite Thin Films for Hydrogen Production

Yousefzadeh, Samira | 2016

637 Viewed
  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 49213 (04)
  4. University: Sharif University of Technology
  5. Department: Physics
  6. Advisor(s): Moshfegh, Alireza
  7. Abstract:
  8. World population growth, depletion of fossil fuels resources depletion and increased air pollution resulting from their consumption, human society has had to replace fossil fuels with renewable sources. In this context, the production of hydrogen using solar energy is feasible candidate to replace fossil fuels, which can be produced by water splitting in a photoelectrochemical (PEC) cell using an appropriate photocatalyst. This clean production method has been attended by many researchers in recent years. The most common photocatalyst for the conversion of sunlight to hydrogen by splitting water is Titanium dioxide (TiO2). But high energy gap and fast electron-hole recombination rate in TiO2 has limited its use in photoelectrochemical cells. In the first part of this study, by applying characteristic physical properties of Graphene, TiO2/Graphene nanocomposite thin film was synthesized by sol-gel method and was used as a photoanode in photoelectrochemical cell. According to physical, chemical and photoelectrochemical analysis, it was found that the Graphene increases effective surface area for absorption of water and the fast transfer of hole for water oxidation reaction at the interface between the electrolyte and photoanode as well as separation and charge transport in photoanode and thus, improves the water oxidation and reduction reactions. Then, to increase the absorption of visible light, TiO2/Graphene nanocomposite thin film was modified with CdS nanoparticles by Successive ion layer adsorption and reaction process (SILAR) method with 10, 20, 30 and 40 cycles for using in photoelectrochemical cells. The results showed that CdS nanoparticles increased visible light absorption in the CdS/TiO2/Graphene nanocomposite and maximum transient electron lifetime (5 s), photocurrent density (about 4.5 A/m2) and solar to hydrogen efficiency (0.28%) was obtained for the optimized 30 cycles. Moreover, to increase separation and charge transport in Bismuth Vanadate (BiVO4) as visible light active semiconductor, BiVO4/Graphene was synthesized and used for TiO2 modification. Based on the results, photcurrent density and maximum solar to hydrogen conversion efficiency was obtained at about 1.3 A/m2 and 0.12% for the BiVO4/Graphene/TiO2 nanocomposites photoanode, respectively. These results show increasing values as compared to the TiO2 and BiVO4/Graphene photoanodes. The enhanced efficiency is due to presence of Graphene resulting in increased visible light absorption, surface area at the photoanode/electrolyte interface as well as ease of charge carrier separation and transport. In addition, to improve the optical and electrical properties of TiO2, its Nanowires structure was synthesized by hydrothermal method and then, Graphene quantum dots (GQD) with high electrical conductivity and ability to absorb of visible light were deposited on the TiO2 Nanowire (TiO2 NW) film. Based on the obtained results, photocurrent density and maximum solar to hydrogen conversion efficiency was attained for the GQD/TiO2 NW nanocomposite photoanode at about 29.7 A/m2 and 1.58%, respectively. The enhanced photocurrent density of 8-fold and solar to hydrogen conversion efficiency of 6-fold was measured as compared to the TiO2 NW photoanode. Thus, Graphene quantum dots in the GQD/TiO2 NW nanocomposite increased the visible light absorption and charge transport in photoanode components as well as at the electrolyte/photoanode interface. Also, light absorption, charge transfer for water oxidation and reduction processes and PEC efficiency at GQD/TiO2 NW nanocomposite photoanode improved as compared to the other studied systems, in this research
  9. Keywords:
  10. Titanium Dioxide ; Photoelectrochemical Cell ; Graphene ; Visible Light ; Load Transform ; Charge Transfer Compounds ; Solar Conversion Efficiency

 Digital Object List

 Bookmark

No TOC