Novel carbon-doped TiO2 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 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-C-x(x)) 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.