Indium Clusters With 6s² Lone-Pair Effect as Excitonic Electron Reservoirs for Direct 2e^- Photocatalytic H₂O₂...

The intrinsic activity-selectivity trade-off in photocatalytic 2e^- oxygen reduction reaction (ORR) for H₂O₂ photosynthesis originates from the kinetic dilemma between weak O₂ adsorption at single-atom sites and unfavorable O-O cleavage at multimetal sites. Herein, we demonstrate that indium (In) clusters with a unique 6s² lone-pair effect can break this long-standing single-atom/cluster trade-off by acting as excitonic electron reservoirs on carbon nitride. InSAC-DCN delivers a remarkable H₂O₂ generation rate of 1930.8 µmol∙g^-1∙h^-1 with selectivity exceeding 90%, far surpassing both pristine carbon nitride and In single-atom counterparts. Combined fs-TAS and in situ characterizations reveal that In clusters enable ultrafast exciton dissociation and instantaneously deliver electrons to the geometric Yeager-type side-on O₂ adsorption site, thereby favoring direct 2e^- H₂O₂ formation. DFT calculations elucidate lowered energy barriers for ∗OOH formation, suppressed O-O dissociation, and accelerated water dissociation. Meanwhile, the synergistic coupling between water oxidation and ORR establishes a self-sustained proton-feedback loop for enhanced overall efficiency. This work highlights that exciton engineering coupled with p-block metal clusters enables efficient and selective 2e^- ORR beyond conventional single-atom strategies to overcome the activity-selectivity trade-off, establishing a distinct material-design paradigm for high-performance photocatalysts toward H₂O₂ photosynthesis.