Storage Of Energy Generated At UV-irradiated TiO₂,Photocatalyst And Its Conversion

The photocatalyst systems with energy storage abilities have been developed by coupling semiconductor elelctrodes with energy storage materials. In these systems light energy is directly converted to chemical energy. TiO2is an n-type semiconductor with large bandgap, and its useful functions generally originate from reductive and/or oxidative reactions driven by photogenerated electrons and holes at UV-irradiated TiO2surfaces. This thesis focuses on oxidative energy storage of TiO2/Ni(OH)2composite film system and simultaneous storage of oxidative and reductive energy generated at a UV-irradiated TiO2.In the third chapter, TiO2nanorod arrays were in situ prepared on FTO substrates by a facile hydrothermal synthesis. The three-dimensional (3D) nanostructured TiO2-Ni(OH)2composite film electrode was further fabricated by a novel electrochemical procedure using the TiO2nanorod array as substrate. The UV-induced oxidative energy storage behaviors of the3D nanostructured TiO2-Ni(OH)2composite film system were investigated by cyclic voltammetry and irradiation-discharge cycles. The IPCE value was calculated to be10.6%, and the system exhibited good reversibility. TiO2nanorod arrays supply direct electrical pathways for photogenerated electrons, increasing the electron transport rate. The ordered3D nanoporous structure not only offers the large p-n junction area but also provides easy access of the surfaces to liquid electrolyte. For the composite film-platinum coupling system, the photogenerated electrons and holes separate easily because of the large potential difference. The three factors above are responsible for the enhanced oxidative energy storage of the obtained3D nanostructured TiO2-Ni(OH)2composite film.In the fourth chapter, WO3nanoflake arrays were prepared on FTO substrate by a hydrothermal synthesis. TiO2-Ni(OH)2composite film electrode was fabricated by a cathodic electrodeposition using the TiO2nanorod arrays as substrate. A novel storage system was first constructed by galvanically coupling the as-prepared TiO2-Ni(OH)2 composite film with the WO3film electrode. The coupling of the UV-irradiated TiO2-Ni(OH)2composite film with the WO3nanoflake array electrode in the dark decreases the hole-electron recombination and the reduction of NiOOH, leading to the simultaneous storage of UV-induced oxidative and reductive energy, and the enhancement of the oxidative energy storage ability.