Hierarchical Ta-Doped TiO₂ Nanorod Arrays with Improved Charge Separation for Photoelectrochemical Water Oxidation under FTO Side Illumination.

TiO₂ is one of the most attractive semiconductors for use as a photoanode for photoelectrochemical (PEC) water oxidation. However, the large-scale application of TiO₂ photoanodes is restricted due to a short hole diffusion length and low electron mobility, which can be addressed by metal doping and surface decorating. In this paper we report the successful synthesis of hierarchical Ta doped TiO₂ nanorod arrays, with nanoparticles on the top (Ta:TiO₂), on F-doped tin oxide (FTO) glass by a hydrothermal method, and its application as photoanodes for photoelectrochemical water oxidation. It has been found that the incorporation of Ta in the TiO₂ lattice can decrease the diameter of surface TiO₂ nanoparticles. Ta:TiO₂-140, obtained with a moderate Ta concentration, yields a photocurrent of ∼1.36 mA cm at 1.23 V vs. a reversible hydrogen electrode (RHE) under FTO side illumination. The large photocurrent is attributed to the large interface area of the surface TiO₂ nanoparticles and the good electron conductivity due to Ta doping. Besides, the electron trap-free model illustrates that Ta:TiO₂ affords higher transport speed and lower electron resistance when under FTO side illumination.