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

ABSTRACT Achieving efficient solar‐to‐chemical conversion for H 2 O 2 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 Bi 3+ sites on an In 2 S 3 semiconductor host to achieve efficient solar H 2 O 2 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 O 2 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–In 2 S 3 photocatalyst achieves an H 2 O 2 production rate of 368.8 µM h −1 in pure water, far surpassing pristine In 2 S 3 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.