A rapid cathodization can simultaneously dope Nb5+ , Ti3+, and oxygen vacancy (Ov) into anodically grown anatase TiO2 nanotube array (TNA). Compared with the self-doped blue TNA, the Nb-doped TNA (Nb-TNA with ∼2 at% Nb) marked superior photoelectrochemical (PEC) water oxidation, with photocurrent density of 1.25 mA cm−2 at 1 V Ag/AgCl in NaClO4 under 1 sun illumination. Enhanced PEC activity arises from improvements in light harvesting via mid-gap-states, electrical conductivity, and interfacial charge transfer (82 % efficiency), associated with ∼0.7 eV valence-band-edge shift (versus intact TNA) by near-surface-enriched peroxo-species. The photogenerated holes on Nb-TNA with stronger oxidizing power promoted ·OH formation to attain superior solar PEC degradation rates for nitrobenzene (0.95 h−1) and benzoic acid (0.25 h−1), alongside stoichiometric H2 generation (22.5 µmol h−1) on Pt cathode with long-term stability. With sulfate ions, persulfate/sulfate radical formation affected the oxidation rate in compound-specific manner and overall decreased photocurrent.​