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作者 Shankar, Karthik
書名 Effect of architecture and doping on the photoelectrochemical properties of titania nanotubes
國際標準書號 9780549046608
book jacket
說明 244 p
附註 Source: Dissertation Abstracts International, Volume: 68-05, Section: B, page: 3331
Thesis (Ph.D.)--The Pennsylvania State University, 2007
N-type nanocrystalline titania has attracted significant attention in the scientific community for its unique properties such as size quantization effects, large specific surface area and the possibility of large-scale use in high-efficiency semiconducting photoelectrochemical cells. While the nanocrystalline titania typically used in photoelectrochemical cells is prepared from a colloidal sol of nanoparticles, the titania nanotubes in the present study are robust immobilized structures grown anodically upright to form a compact self-organized non-particulate film
This dissertation investigates the effect of the formation parameters such as the anodization potential, the concentration of water and fluoride species in the anodization electrolyte, the nature of the cation, the anodization temperature and the nature of the solvent used on the architecture of TiO 2 nanotube arrays fabricated by anodization of a starting Ti foil in a fluoride ion containing electrolyte. By varying the nature of the anodization electrolyte, an unprecedented degree of control over the architecture of TiO 2 nanotube arrays has been achieved. Nanotube arrays ranging from 0.1 mum to 100 mum in length, wall-thickness from 6 nm to 34 nm and pore diameters ranging from 12 nm to 250 nm were fabricated. While the nanotube length in all-aqueous electrolytes is limited to less than 10 mum, nanotube lengths as great as 360 mum were obtained by employing organic solvents in conjunction with water. The fast formation of very long high-aspect ratio TiO2 nanotubes in electrolytes containing formamide and ethylene glycol are considered in terms of a growth model. It is suggested that faster high field ionic conduction through a thinner barrier layer is responsible for the higher growth rates observed in electrolytes containing formamide and ethylene glycol
Also examined are the photoelectrochemical properties that result as a consequence of the nanotubular architecture of TiO2. The magnitude of the anodic photocurrents obtained from the nanotube photoelectrodes under band-gap illumination are significantly higher than that reported for any other form of nanocrystalline titania. Open circuit voltage decay experiments revealed that the electron recombination lifetimes in titania nanotube array photoelectrodes are superior to those in nanoparticulate electrodes of similar thickness and as a consequence, the nanotubular electrodes are expected to have superior charge collection efficiencies. Under band-gap illumination, 30 mum long TiO2 nanotube array based photoanodes performed photo-assisted water splitting at an efficiency as high as 16.25%. Anionic doping of TiO 2 nanotube arrays has been investigated as a technique to extend the photoresponse of titania into the visible region with emphasis on the carbon and nitrogen as dopants. An electrochemical doping technique was successful in introducing a nitrogen doping level as high as 12% with nitrogen occupying the photoelectrochemically useful substitutional sites in the TiO2 lattice instead of the more typical interstitial sites
The nanotube arrays have an extremely large internal surface area compared to a planar surface. TiO2 nanotube arrays 20 mum in length and with a pore diameter of 90 nm are found to have an internal surface area 3000 times that of a planar unstructured film. Dye sensitized solar cells using different architectures and dyes have been constructed and photoconversion efficiencies as high as 6.9% have been demonstrated
School code: 0176
Host Item Dissertation Abstracts International 68-05B
主題 Engineering, Electronics and Electrical
Engineering, Materials Science
Alt Author The Pennsylvania State University
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