Nageh Allam - Photoelectrochemical Water Oxidation Characteristics of Anodically Fabricated TiO2 Nanotube Arrays: Structural and Optical Properties

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      Publication Details (including relevant citation   information):

      J. Phys. Chem. C, 2010, 114 (27), pp 12024–12029

      Abstract:

      There are currently immense needs to optimize low-cost materials,   such as TiO2, so they can efficiently split water   photoelectrochemically into hydrogen and oxygen, thus providing a   clean energy fuel. To this end, the nature of the crystalline   phase and the dimension of the photocatalyst are of crucial   significance. In this study, films of 7 μm long titania nanotube   arrays were fabricated via anodization of titanium foil in   formamide electrolytes containing NH4F and   H3PO4. Upon annealing the as-anodized   nanotubes, the anatase-to-rutile phase transformation was found   to start at 550 °C, which is about 120 °C above the temperature   observed for the 500 nm long nanotube films, with the nanotube   films remaining stable up to 580 °C. Analysis of the variation of   crystallite size with annealing temperature along with XPS   analysis of the films was used to investigate the reason behind   this observation. UV−vis measurements showed that the absorption   edges of the annealed samples were red shifted from that of the   as-anodized sample. The stabilization of the anatase phase up to   550 °C, while keeping the tubular structure in place, is very   significant as anatase is the most photoactive polymorph of   titania. Besides, the 7 μm long nanotubular structure provides a   large surface medium for light utilization through scattering.   Used as photoanodes to photoelectrochemically split water, the   580 °C crystallized nanotube arrays showed a three-electrode   photoconversion efficiency of 10% under UV illumination (100   mW/cm2, 320−400 nm, 1 M KOH).

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