Surface polarization enables high charge separation in TiO₂ nanorod photoanode

Poor charge separation efficiency of semiconductors often stands in the way of photoelectrochemical (PEC) water splitting realization. In this report, a surface polarized TiO₂ photoanode is obtained via –OH moiety decoration, which achieves a fundamentally improved charge separation efficiency of about 94% at 1.23 V_RHE. Detailed data shows that these hydroxyls with electric dipoles polarize the surface, inducing substantial electric field in the surface region, and elevating band edges so as to form a homojunction within TiO₂. Such serves as the direct driving force for the photogenerated charge separation and migration. Moreover, these hydroxyls also facilitate water oxidation kinetics. Without typical doping or cocatalyst, surface polarized TiO₂ photoanode delivers a considerably increased photocurrent density of about 1.41 mA·cm⁻² at 1.23 V_RHE (AM 1.5 G) and a cathodic shift on onset potential over 200 mV. This report highlights new opportunities to modulate charge separation by surface polarization for the construction of robust photoanodes.