| Titanium dioxide (TiO2) with the advantages of good chemical stability, anti-light corrosion, non-toxicity and low cost has wide application prospects in the fields of photoelectric conversion and photo catalysis. However, TiO2 can only absorb UV light below the wave length of 387 nm due to its wide band gap, which only accounts for about 4% of the total solar energy. Moreover, the high recombination rate of photo-electron and -hole limits its photoelectrochemical catalytic application. So, the development of TiO2 photocatalyst with high visible-light-response as well as its new applications is one of the most important tasks in the photocatalytic fields.This thesis focuses on improving the photocatalytic activity of TiO2 as well as the applications in the photoelectric conversion fields. The N-doped TiO2 was prepared using sol-gel and magnetic sputtering methods, and then was coupled with NiO thin film to form a new kind of TiO2 composite film. The TiO2 nanotube arrays were prepared by anodizing method using Ti as substrate, then filled with CdS and Ni(OH)2 to prepare TiO2/CdS and TiO2/Ni(OH)2 composite thin films, respectively. The synthesis, characterizations and photoelectrochemical properties of the as-formed samples were investigated by SEM, XRD, XPS, UV-Vis absorption\transmittance spectroscopy and photoelectrochemical tests. The main results are as follows:1. The TiO<sub>2-xNx thin film was formed on ITO glass substrate by using sol-gel and magnetic sputtering methods, respectively. Then a highly porous NiO film was deposited on the surface of ITO/TiO<sub>2-xNx film by chemical bath deposition (CBD) to fabricate ITO/TiO<sub>2-xNx/NiO composite thin film electrodes, which showed good photo-electrochromic properties and light energy storage ability.The TiO<sub>2-xNx thin films were prepared by sol-gel method, and the effects of raw material ratio and annealing temperature on the photoelectric properties were also discussed. It was found that the samples prepared with different molar ratios of CO(NH2)2 to (C4H9O)4Ti had a redshift to the range of 450600 nm, and among them, the sample prepared with the molar ratio of 4 showed the most obvious redshift. Meanwhile, the ITO/TiO<sub>2-xNx samples annealed at 400 and 500℃showed excellent photoelectrical properties. The ITO/TiO<sub>2-xNx/NiO electrode annealed at 400℃possessed an excellent photochromic property. When the color of` the electrode turned from colorless to brown, the transmittance varied at 400 nm was as high as 50% and the discharge time was 4.2 h at 100 nA. The results showed that ITO/TiO<sub>2-xNx/NiO composite electrode exhibited the good ability for reversible photochromism and energy storage.When the ITO/TiO<sub>2-xNx films were prepared by magnetic sputtering method, the effects of gas flow ratio of N2/O2 and annealing temperature on the photoelectrochemical properties of TiO<sub>2-xNx thin films were investigated. It was found that the ITO/TiO<sub>2-xNx film prepared with the O2/N2 flow ratio of 1:2 annealed at 400℃showed excellent light response, and its coupled ITO/TiO<sub>2-xNx/NiO composite film had excellent photochromic and energy storage properties. After 1 h irradiation, the variance ratio of its UV-Vis transmittance at 500 nm was up to 82%, and the discharge time was 11.1 h at 100 nA, indicating excellent energy storage and photochromic properties.The NiO film deposited on the surface of the TiO<sub>2-xNx by chemical bath deposition method showed a porous structure, which contributes to the transfer of photoinduced species and facilitates electrolyte into the film. While TiO<sub>2-xNx was irradiated by light, the photogenerated holes would oxidize NiO to NiOOH, and the color of the electrode changed from gray to dark brown. As a result, the electrode was photocharged.2. The TiO2 nanotube arrays were prepared by anodizing method and CdS/TiO2 photocatalytic composite electrodes were prepared by a.c electrodeposition method. The effect of different solutions and technical parameters on the morphology, microstructure and photoelectrochemical properties was investigated. The results disclosed that TiO2 nanotube arrays can be fabricated on the surface of Ti substrate in amine fluoride and glycerol aqueous solution. The diameter of the TiO2 nanotube ranged from 100 to 200 nm, with a wall thickness of ca.10 nm and a tube length of ca.1 um. And then, CdS particles were deposited on the surface of the nanotubes by a.c electrochemical deposition method, forming a CdS/TiO2 photocatalytic composite electrode. The microstructure and morphology of CdS particles were determined by the deposition time. Under UV-visible light irradiation, the absorption edges of CdS/TiO2 composite films showed the features of the two kinds of semiconductors, ranging from 385 to 520 nm, and the red shift of the absorption edge increased with deposition time. The CdS/TiO2 composite film prepared with 3 min deposition of CdS showed the best photoelectrochemical properties and the fastest degradation of OM under Hg light irradiation.3. The TiO2 nanotube array/Ni(OH)2 composite electrode was prepared by the cathodic deposition of Ni(OH)2 on the TiO2 nanotube array. The photoelectrochromic properties and energy storage ability were evaluated. It was found that TiO2/Ni(OH)2 composite film electrode had an excellent photochromic and energy storage property, and its discharge time was up to 19.4 h at 100 nA after 2 h irradiation, which showed excellent photocharging ability and may be used in the photochromic and photoelectrochemical cells.
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