Clarifying the Direct Generation of ^•OH Radicals in Photocatalytic O₂ Reduction: Theoretical Prediction Combined with Experimental Validation

This work systematically studied thermocatalytic and photocatalytic pathways of formaldehyde degradation and H-assisted O₂ reduction over a Pt₁₃/anatase-TiO₂(101) composite via DFT calculations together with constrained molecular dynamics (MD) simulations. We show that photocatalytic O₂ reduction on Pt/TiO₂ can directly generate ^•OH radicals (*O₂ → *OOH → ^•OH) via two hydrogenation steps with small barriers, and the product selectivity (*H₂O₂ or ^•OH) is decided by the relative position between catalyst Fermi level and ^•OH/*H₂O₂ redox potential (theoretical determination of 0.07 V referencing to the SHE). Such a novel reaction channel was furthermore validated at the liquid-solid interface via constrained MD simulations and experimental electron paramagnetic resonance detections, and a wide range of H resources, e.g., *HCHO, *HCO, *H (H⁺ + <i>e</i>^<i>-</i>), can always drive the direct ^•OH generation. The additional portion of <i>e</i>^<i>-</i>-triggered ^•OH radicals are prone to diffuse into solution or the TiO₂ surface and furthermore cooperate with the conventional <i>h</i>^<i>+</i>-driven photooxidations.