Photoelectrochemical properties of titania nanotubes
- PDF / 609,971 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 23 Downloads / 247 Views
N-type nanocrystalline titania is a promising material for use in semiconductor photoelectrochemical cells and, potentially, the solar generation of hydrogen. In this study, we examined the photochemical properties of titania nanotube arrays made by anodization of a starting Ti foil in a fluoride ion containing electrolyte. The absorption properties of the titania nanotube samples were investigated using diffuse reflectance ultraviolet (UV)-visible (vis) spectroscopy, with a broadening of the absorption spectra seen as a function of material phase, nanotube diameter, and Pd sensitization. The magnitude of the anodic photocurrent obtained from the polycrystalline nanotube samples, measured under band gap UV illumination, appeared to be significantly higher than that reported for any other form of nanocrystalline titania. A maximum photoconversion efficiency (UV light exposure at 365 nm, intensity 146 mW/cm2) of 4.8% was obtained for 22 nm diameter nanotubes annealed at 500 °C and coated with a discontinuous palladium layer of 10 nm average effective thickness.
I. INTRODUCTION
In 1972 Fujishima and Honda reported the photocatalytic splitting of water on TiO2 electrodes1 N-type nanocrystalline titania is a promising material for use in semiconductor photoelectrochemical cells and is the subject of numerous recent studies2–5 due to its favorable bandstructure for water-splitting, low cost, and exceptional corrosion resistance in a wide variety of aqueous electrolytes. We note that the development of a useful semiconductor photocatalyst requires material architectures that maximize surface area and optimize crystallite morphology, thus increasing the amount of photogenerated charge. A further requirement is the feasibility of excitation by readily available solar radiation, however the large band gap of titania (3.0–3.2 eV for the anatase and rutile phases) precludes efficient photoconversion by visible light which comprises approximately 95% of the solar spectrum. Modifying the band gap structure of titania to make it responsive to a larger portion of the solar spectrum is a prized, and quite worthy scientific goal. Various approaches to modifying the band gap include sensitization with dyes,6 doping with transition metals,7,8 carbon,9 or nitrogen,10–12 and partially covering the surface with catalytic materials such as Au13,14 or Pd.15,16 As material architectures are scaled to the nanometer regime their electronic and optical properties frequently
a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2004.0370 J. Mater. Res., Vol. 19, No. 10, Oct 2004
http://journals.cambridge.org
Downloaded: 09 Jan 2015
show profound changes.17 The nanostructured titania used in previous photochemical studies were obtained by casting a colloidal sol, with the resulting film consisting of a three-dimensional network of interconnected nanometer-sized particles. The small size of the crystalline particles, generally 艋50 nm, results in ultrahigh surface-to-volume ratios. In both nanoparticula
Data Loading...
