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

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.