Preparation Of TiO₂ Nanotube By Anodization And Their Applications In Dye-sensitized Solar Cells And Photocatalysis

TiO2 nanomaterials have been applied extensively in senser, dielectric material, self-cleaning materials, photocatalyst and dye sensitized solar cells due to its advantages in rich resources, nontoxicity, and chemical stability. In recent years, TiO2 nanotubes have been applied in dye-sensitized solar cells, photocatalysts, etc. due to their large specific surface area and aspect ratio. Among many mehods for generating nanotubes, anodization is an excellent method with various advantages, including controllable morphology, large-area preparation. In our work, we employed anodization method to prepare TiO2 nanotubes. The growth mechanism was described in detail. Finally, the nanotubes were embedded into the photoanode of dye-sensitized solar cells (DSSC) and used as efficiency catalyst for photocatalysis.1. We synthetized highly aligned TiO2 nanotube arrays by anodization and studied the growth mechanism of TiO2 nanotube by analyzing the current-time curve for the anodization process. Moreover, we studied various influencing factors for formation of TiO2 nanotubes, that were applied voltage, tempreture, and stirring rate. We concluded that we can enhance the oxidize rate by increasing applied voltage and reaction temperature. The effect of stirring rate is the same as that of reaction tempreture. Subsequently, Cu was doped in anodic nanotube by directly adding Cu(NO3)2 in the electrolyte. The evolution of Cu doped TiO2 nanotubes was ruled by the same law as that of pure TiO2 nanotubes.2. We prepared TiO2 hierarchically structured arrays by anodizing a sputterred Ti membrane and studied the formation mechanism. The current-time curves during the preparation process were also recorded for the purpose of investigating the formation of hierarchically structured TiO2 arrays.. Subsequently, we applied TiO2 hierarchically structured TiO2 arrays as photoanode for DSSC. The film thickness dependant photovohaic properties of DSSC are discussed.3. TiO2 nanotubes prepared by anodization and P25 nanoparticles were used to prepare TiO2 paste, including pure TiO2 nanotubes (NT) paste, TiO2 nanoparticle (NP) paste and nanoparticle/nanotube (NPNT) paste. The pastes were doctor-bladed on FTO glass to form different structures. Then we investigated the photovoltaic characterization of the NPNT film based DSSC. Due to NPNT film combining the advantages of NT film (higher FF) and NP film (larger Jsc), the NPNT film based DSSC achieves great improvement with a total energy conversion efficiency of 4.96%, which is 18.6% larger than NP film and is 1.5 times larger than NT film. It is demonstrated that the improved efficiency of NPNT film can attributed to the fast electron transport route, namely "electron expressway". The electron expressway shortens electron transport route and decreases electron-hole recombination rate, which result in the decrease of electron transport resistance and the improvement of electron transport efficiency, and accordingly the improvement of FF and total efficiency.4. We have synthesized a sandwiched structure of TiO2-based nanotubes/nanoparticles/nanotubes film as photoanode of DSSCs. An improved total energy-conversion efficiency of 6.11% was obtained in the sandwiched film, which is 27.3%,46.1%, and 213% higher than those in the double-layered film, the nanoparticle film and the nanotube film, respectively. Combined the light absorbtion data, the improvement of the sandwiched film based DSSC could be owing to effective scattering by the bottom layer and reflection of escaped light by the top layer, which increased the optical route in sandwiched film and thus light harvesting efficiency. The improvement of light harvesting efficiency lead to the enhancement of Jsc and total efficiency. Moreover, a modified multilayer composite structure of nanotube/composite/nanotube film was synthesized and applied in dye sensitized solar cells. Compared with the composite film and the sandwiched film based DSSCs, the multilayer composite film based DSSC exhibits more excellent photovoltaic performance with a total efficiency of 7.17%. Combined with the light-absorption data and the previous work, it is concluded that the improvement of total efficiency for the multilayer composite film benefits from the combined utilization of effective light-scattering and high-efficiency electron transport.5. We studied the photocatalytic performance of TiO2 nanotubes and Fe-coated TiO2 nanotubes with different contents. The results from experiments indicate that Fe-coated TiO2 nanotubes with a appreciate concentration would improve photocatalytic efficiency compared to the pure TiO2 nanotube but excessive Fe coating would instead decreases photocatalytic efficiency. This could be explained as Fe ions may play a role as e- or h+ traps and the existence of Fe ions reduces e-/h+ pair recombination rate and thus improves photocatalytic efficiency. However, excessive Fe ions could act as electron or hole recombination center, which decrease photocatalytic efficiency immensely.