Enhancement of the photoinduced hydrophilic conversion rate of TiO2 film electrode surfaces by anodic polarization

Changes in hydrophilicity of TiO2 film electrode surfaces by UV light irrad iation in an aqueous solution were investigated under potential-controlled conditions. Although no change was observed when the electrode potential of TiO2 was set around its flat-band potential E-fb, the photoinduced hydroph ilic conversion proceeded at potentials positive of Efb. The hydrophilic co nversion rate increased with larger positive potentials, but the addition o f hole scavengers decreased the rate, suggesting that the diffusion of phot ogenerated holes to the surface is the important process for the hydrophili c conversion. Based on these results, we propose a model in which the photo induced hydrophilicity is initiated by two-hole trapping by a surface latti ce oxygen, producing an oxygen defect, followed by the dissociative adsorpt ion of a water molecule at the defect site.