Oxygen Vacancy Engineering of Metal Oxide Materials for Photoelectrochemical Water Splitting

Photoelectrochemical (PEC) water splitting presents a promising route for sustainable hydrogen production, yet the efficiency of metal oxide photoanodes remains limited by suboptimal light absorption, charge carrier recombination, and sluggish surface reaction kinetics. This review critically examines the strategic engineering of oxygen vacancies (OVs) as a powerful tool for overcoming these intrinsic limitations. We systematically analyze established methodologies for the deliberate introduction and modulation of OVs in metal oxides, including techniques such as the hydrothermal method, thermal treatment, chemical reduction, plasma processing, elemental doping, and microwave heating. Furthermore, we critically evaluate the applicability, strengths, and limitations of key characterization techniques for detecting and quantifying OVs. Crucially, the review delves into the profound mechanistic impacts of OVs on the PEC process chain: Their roles in tailoring electronic band structures to alter the photoelectrochemical properties of metal oxide photoanodes, thereby enhancing visible light absorption, acting as shallow donors to improve charge carrier density, functioning as electron traps to suppress bulk recombination, and modifying surface states to accelerate the oxygen evolution reaction. We also present detailed case studies focusing on five prominent photoanode materials: TiO₂, α-Fe₂O₃, BiVO₄, WO₃, and ZnFe₂O₄. This review elucidates the specific roles and operational principles of OVs within these materials and summarizes the intrinsic relationship among OV generation, characterization, and functional enhancement, providing valuable insights for the rational design of OV-engineered photoanodes toward efficient solar fuel production.