Hydrated Electron‐Induced Oxygen Vacancies in Perovskite Oxide

ABSTRACT Oxygen vacancies (OVs) are crucial for modulating perovskite properties, but their traditional creation typically leads to phase separation or surface contamination, rarely providing clean model systems for fundamental research. Herein, we show that aqueous electron (e aq ‒ ) can selectively reduce transition metal cations (e.g., B‐site in ABO 3 ) at the perovskite surface: B n+ + e aq ‒ → B (n‐1)+ . This reduction weakens the B─O bond, facilitating oxygen ion (O 2− ) release to maintain charge balance, creating OVs and leaving behind localized electrons trapped at the reduced B‐site. The concentration of OVs can be tuned by varying the flux/dose of e aq ‒ during 60 Co‐rays induced water radiolysis. This allows for precise OVs engineering on surfaces or near‐surface regions under mild conditions, which is a challenge with bulk thermal reduction. By tracking charge carrier dynamics at the femtosecond timescale, we underscore an exponential correlation between OVs content and enhanced electron‐phonon coupling constant. This accelerated charge separation well aligns with the observed photocatalytic CO 2 ‐to‐CO conversion performance. Therefore, by establishing a quantitative link between – e aq ‒ ‐tuned concentration of OVs and accelerated electron‐phonon coupling, our work not only enables green, precise surface defect engineering, but also provides a clean model system to unravel the intrinsic role of OVs in catalysis.