Novel Carbon-Doped TiO2 Nanotube Arrays with High Aspect Ratios for Efficient Solar Water Splitting

Abstract
The photocatalytic splitting of water into hydrogen and oxygen using solar light is a potentially clean and renewable source for hydrogen fuel. 1,2 There has been extensive investigation into metal-oxide semiconductors such as TiO2, WO3, and Fe2O3, which can be used as photoanodes in thin-film form. 3-5 Of the materials being developed for photoanodes, TiO2 remains one of the most promising because of its low cost, chemical inertness, and photostability. 6 However, the widespread technological use of TiO2 is hindered by its low utilization of solar energy in the visible region. In this study, we report the preparation of vertically grown carbon-doped TiO2 (TiO2-xCx) nanotube arrays with high aspect ratios for maximizing the photocleavage of water under white-light irradiation. The synthesized TiO2-xCx nanotube arrays showed much higher photocurrent densities and more efficient water splitting under visible-light illumination (> 420 nm) than pure TiO2 nanotube arrays. The total photocurrent was more than 20 times higher than that with a P-25 nanoparticulate film under white-light illumination.