Shining light on oxygen vacancies in SrTiO3 for photocatalytic hydrogen production.

Strontium titanate stands out as a model perovskite for solar-driven hydrogen production as a sustainable energy vector due to its excellent thermal stability, chemical robustness, and tunable electronic structure. However, its wide band gap and rapid charge carrier recombination limit its practical efficiency under solar irradiation. Oxygen vacancies are often used to overcome these bottlenecks, but their role is not unique: surface oxygen vacancies can promote adsorption/activation and assist interfacial charge transfer, whereas excessive or bulk-dominated defects tend to introduce deep states that accelerate recombination. This review discusses how oxygen vacancies are formed in SrTiO3 (thermal reduction, hydrogenation, chemical reduction, and synthesis-driven nonstoichiometry), and how vacancy location and concentration can change band alignment, carrier lifetimes, and hydrogen-evolution kinetics. By comparing representative reports under both sacrificial and overall water-splitting conditions, the review highlights how vacancy engineering is method-dependent and must be interpreted together with surface chemistry and cocatalyst interfaces. This review also summarizes key characterization strategies, including XPS, XAS, EPR, and DFT, for distinguishing surface and bulk oxygen vacancies in SrTiO3-x photocatalysts.