Novel carbon-doped TiO ₂ nanotube arrays with high aspect ratios for efficient solar water splitting

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 TiO ₂, WO ₃, and Fe ₂O ₃, which can be used as photoanodes in thin-film form. ^3-5 Of the materials being developed for photoanodes, TiO ₂ remains one of the most promising because of its low cost, chemical inertness, and photostability. ⁶ However, the widespread technological use of TiO ₂ 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 TiO ₂ (TiO _2-xC _x) nanotube arrays with high aspect ratios for maximizing the photocleavage of water under white-light irradiation. The synthesized TiO _2-xC _x nanotube arrays showed much higher photocurrent densities and more efficient water splitting under visible-light illumination (> 420 nm) than pure TiO ₂ nanotube arrays. The total photocurrent was more than 20 times higher than that with a P-25 nanoparticulate film under white-light illumination.