Interactions of Oxygen Vacancies with Photoinduced {Hole/Electron} Pairs in SrTiO3–x: Their Key Role in Photocatalytic H₂ Production

The present work elucidates the role of lattice oxygen vacancies (Vos) 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. Vo-enriched STO materials (Vo-STO) were synthesized via anoxic flame spray pyrolysis (A-FSP) technology that allowed production of a library of SrTiO3–x nanomaterials with controlled Vo concentrations. The optimal Vo-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 Vos) 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 Vo population results in a slight upshift of flat band potential (Efb) and decreases the interfacial charge-transfer resistance, hence enhancing photocatalytic activity. Furthermore, open-circuit potential decay measurements reveal longer e–/h+ carrier lifetimes in Vo-rich SrTiO3–x. The present findings highlight the potential of Vo-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 Vo-enriched perovskite nanomaterials.