Spatially Decoupled Cascade Oxygen Reduction on Bi Single‐Atom and Cluster‐Hybrid Sites for Hydroxyl Radical Generation

The two‐electron oxygen reduction reaction (2e − ORR) for H 2 O 2 production and the subsequent in situ activation to ·OH are constrained by linear scaling relationships, making it difficult for a single active site to simultaneously optimize O 2 activation and H 2 O 2 conversion. This work overcomes the trade‐off by spatially decoupling the cascade reaction onto single‐atom and cluster‐hybrid sites and employing photoelectrocatalysis (PEC). Through a ligand‐exchange and pyrolysis route derived from a metal–organic framework precursor, Bi single atoms and clusters are co‐anchored on B‐doped TiO 2 . The hybrid interface thermodynamically optimizes the intermediate adsorption energies to ensure cascade selectivity, whereas PEC kinetically accelerates the H 2 O 2 ‐to‐·OH conversion by supplying photogenerated electrons. Density functional theory and free‐energy diagrams indicate that H 2 O 2 forms at the single atoms and dissociates into ·OH at the clusters, with the relationship between the p‐band center and ·OH yield following the Sabatier principle. The catalyst delivers a ·OH production rate of 250 µM h −1 at neutral pH and remains active over a broad pH range (3–9). Moreover, it enables broad‐spectrum removal of recalcitrant organic pollutants and retains stable performance over 50 h of operation in a flow‐cell reactor. This work offers guidance for designing cascade catalysts at single‐atom and cluster‐hybrid interfaces.