Photoelectrochemical water oxidation in anodic TiO₂ nanotubes array: Importance of mass transfer

In this study, 1-μm-thick TiO₂ nanotubes array was prepared through anodization in aqueous or organic electrolytes, and their photoelectrochemical properties were compared. TiO₂ nanotubes array prepared in an aqueous electrolyte exhibited better intrinsic characteristics for water oxidation, including larger naked surface area, higher oxygen vacancies leading to improved electrical conductivity, higher donor density, and lower valence band edge position, compared to those prepared in an organic electrolyte. However, a higher photocurrent density was observed in the TiO₂ nanotubes array prepared in an organic electrolyte because of facile mass transfer, resulting in effective interaction between the generated holes and reactant.