Deciphering the Role of Bi Single Atoms in Bi‐In ₂ S ₃ for Robust Solar H ₂ O ₂ Photosynthesis: From Adsorption Geometry to Band Structure

Achieving efficient solar-to-chemical conversion for H₂O₂ synthesis is often hampered by fast charge recombination and the competitive side reactions. While single-atom catalysts (SACs) are effective for regulating reaction pathways, the intricate interplay between p-block metal atoms and the electronic structure of semiconductor hosts remains elusive. Herein, we report the construction of atomically dispersed Bi³⁺ sites on an In₂S₃ semiconductor host to achieve efficient solar H₂O₂ synthesis. Density functional theory (DFT) calculations first elucidate the underlying electronic mechanism, identifying a pronounced Bi 6p-S 3p orbital hybridization that narrows the bandgap and enhances band dispersion. Guided by these theoretical insights, experimental characterizations confirm that the resulting Bi-S coordination motifs facilitate efficient interfacial charge separation and induce Pauling-type O₂ adsorption. This adsorption mode significantly lowers the activation barrier for *OOH formation, directing the reaction along the selective 2e⁻ ORR pathway. As a result, the Bi-In₂S₃ photocatalyst achieves an H₂O₂ production rate of 368.8 µM h⁻¹ in pure water, far surpassing pristine In₂S₃ and most reported inorganic photocatalysts. This work highlights the dual functionality of p-block single atoms as both catalytic centers and electronic modulators, providing a robust strategy for unifying light harvesting and reaction-pathway control in photocatalysis.