Interactions of Oxygen Vacancies with Photoinduced {Hole/Electron} Pairs in SrTiO_3–<i>x</i>: Their Key Role in Photocatalytic H₂ Production

The present work elucidates the role of lattice oxygen vacancies (V_os) in SrTiO₃ (STO) nanoparticles on the spin dynamics of photogenerated charge carriers (electrons/holes, e^-/h⁺) and on the photocatalytic hydrogen (H₂) evolution from H₂O. V_o-enriched STO materials (V_o-STO) were synthesized via anoxic flame spray pyrolysis (A-FSP) technology that allowed production of a library of SrTiO_3-<i>x</i> nanomaterials with controlled V_o concentrations. The optimal V_o-STO materials exhibited a 200% increase in photocatalytic H₂ production rates compared with pristine STO. A combined study using electron paramagnetic resonance spectroscopy and photoelectrochemistry reveals that monomeric oxygen vacancies (type-B V_os) are the key factors to boost photoinduced charge separation via suppression of the e^-/h⁺ recombination. Mott-Schottky and electrochemical impedance spectroscopy show that increased surface V_o population results in a slight upshift of flat band potential (<i>E</i> _fb) and decreases the interfacial charge-transfer resistance, hence enhancing photocatalytic activity. Furthermore, open-circuit potential decay measurements reveal longer e^-/h⁺ carrier lifetimes in V_o-rich SrTiO_3-<i>x</i> . The present findings highlight the potential of V_o-spin engineering toward fine-tuning the electronic properties and photocatalytic activity of perovskite oxides. Technology wise, the present study exemplifies A-FSP as a versatile, industrial scale technology for the synthesis of V_o-enriched perovskite nanomaterials.