(271d) Hydrogen Production Via Nanostructured Photocatalytic Titania Thin-Films

The photosplitting of water using solar energy is a potentially clean and renewable source of hydrogen fuel that is environmentally benign and easily distributed. UV-light incident on titanium dioxide electrodes immersed in water have been shown to produce oxygen and hydrogen(1). It has been shown that titanium dioxide photocatalysts(2) have optimal conversion efficiencies in the nanoparticle sizes, as quantum effects become more important. The optimum particle size has been experimentally determined for the degradation of various organics(2, 3), but this optimal particle size has not been determined for the splitting of water. Additionally, there are no reports in the literature indicating how other aspects of the morphology (surface roughness, fractal dimensions, etc.) of the films may affect efficiency of water splitting. Models currently exist that predict the effect of gas-phase deposition conditions on thin film characteristics(4), but many of these conditions have yet to be experimentally verified. In this work, we demonstrate the effect that different process conditions have on the physical (particle size, morphology, crystal structure) and mechanical (adhesion) characteristics of the thin film. Titania films were created via Dip-Coating (DC), Precursor-Vapor Deposition (PVD) or Flame Aerosol Deposition (FAD). A stainless steel support was passed through the flame and the particles deposited onto it via impaction. Process conditions were varied, and the effect on the morphology of the film was explored by AFM, SEM, XRD, UV-Vis and BET. An algorithm was used to determine the fractal dimensions of the films from the AFM images, and correlated to the film deposition conditions. Distinct variations were observed in the resultant fractal dimensions based on the deposition procedure and process parameters. Photocurrents were measured to ascertain the effect that these different physical properties have on the catalytic activity of the films. Films with the best photocurrents were placed in a two-compartment, three-electrode photochemical cell and illuminated with both UV and visible light. Rates of hydrogen production were measured with a GC and correlated to the morphology of the films.

1. Honda, K. & Fujishima, A. (1972) Nature, 238, 37-38. 2. Almquist, C. B., & Biswas, P. (2002) J. of Catalysis, 212, 145-156. 3. Zou, Z., Ye, J., Sakayama, K. & Arakawa, H. (2001) Nature, 414, 625-627. 4 . Kulkarni, P. & Biswas, P. (2003) J. of Nanoparticle Research, 5, 259-268.