Photoexcitation of TiO2 photoanode in water splitting

TiO2 is one of the most promising photoanodes for solar-hydrogen conversion by water splitting. However, the solar-hydrogen efficiency of TiO2 remains limited because of a low photocurrent generation. A clear understanding of photoexcitations within photoanodes can predict the quantity of photocurrent and consequently determine the solar-hydrogen efficiency. In this work, hydrothermally synthesized rutile TiO2 nanorods were investigated for their photoelectrochemical (PEC) performance. A photogenerated hole concentration of TiO2 photoanode was derived as 8.40 × 1014 cm−3 under one sun illumination. In addition, Fermi level pinning associated with high density of surface states was also observed under PEC operation. Base on these results, a series of band diagrams of TiO2 photoanode were established to describe the photogeneration of holes and current at various bias potential. The main limitation of photocurrent generation is the distribution of surface-trapped states, which determines the hole concentration at the surface and consequently determines the open-circuit potential and the photocurrent density.