Photoelectrochemical (PEC) water splitting is a promising approach for generating solar hydrogen. To realize inexpensive PEC devices, TiO₂ has been considered a potential photoanode material because of its abundance, stability, and suitable valence-band energy edge for water oxidation. In this work, we will present results on post-treatment strategies to extend the high efficiencies of these photoanodes to the visible region of the solar spectrum. Our research paper details the successful introduction of different point defects (V_O and V_Ti) in TiO₂ photoanodes using a chemical treatment process. We utilized a range of advanced techniques, including surface photovoltage signal measurement (SPV), electron paramagnetic resonance measurement (EPR), and proton magic angle spinning nuclear magnetic resonance (¹H MAS NMR) to investigate the intrinsic band energy structure and surface state of synthesized TiO₂ photoanodes. Our finding indicates that V_O and V_Ti have favorable effects on photoanodes, leading to enhanced PEC performance. The enhancement is attributed to the interplay of collective and localized effects of point defects on TiO₂. The increased point defects narrow the bandgap and enhance donor density in TiO₂, which increases light absorption, conductivity, and photovoltage, as well as reducing the flat-band potential of TiO₂ photoanodes. Additionally, our results show that the presence of localized surface V_Ti surrounded by O^- increases the amount of surface hydroxyls and creates a more basic environment for Ti-OH species. This facilitates the water oxidation process by serving as trapping sites and self-reduction sites during OER. Our study on OER kinetics, using photoelectrochemical impedance spectroscopy (PEIS) and intensity modulated photocurrent spectroscopy (IMPS), demonstrates that the interaction between collective and localized effects of point defects can decrease the charge transfer resistance on the TiO₂-electrolyte junction and increase the concentration of interface hole flux on TiO₂ photoanodes. This is consistent with the observed higher photovoltage after chemical treatment. Our study has revealed that the interaction between V_O and V_Ti has a significant impact on the PEC performance of TiO₂ photoanodes. We believe that these findings will make a valuable contribution to the development of efficient and stable TiO₂ photoanodes and provide valuable insights into the development of higher performance photoanodes for sustainable energy conversion applications.