Oxygen Vacancy‐Driven Asymmetrical Charge Distribution on Bi‐O‐Sn Sites in Sn‐Doped Bi ₂ MoO ₆ for Efficient Photocatalytic CO ₂ ‐to‐CH ₄ Conversion

Efficient proton-coupled electron transfer (PCET) at tailored active sites is beneficial for photocatalytic CO₂ reduction, yet the relationship between catalytic sites and performance remains unclear. Herein, p-block Sn is introduced into the Bi₂MoO₆ lattice (Sn-BMO) via Bi site substitution to construct a novel oxygen vacancy (Ov)-Bi-O-Sn structure, where high-valence Sn induces Ov formation by lowering the Bi valence state, thereby creating a charge-asymmetrical region. This unique configuration promotes PCET: Sn acts as H₂O oxidation site, enabling proton transfer to proximal Bi site connected to Ov that preferentially traps electrons to convert CO₂. Furthermore, the electronic structure of Bi is modified to optimize Bi 6p-C 2p hybridization for formation of the key intermediate *CHO with low energy barrier. Consequently, Sn-BMO exhibits a remarkable CH₄ evolution rate of 207.3 µmol g^-1 h^-1 with 95.7% CH₄ selectivity in pure water, achieving a record apparent quantum efficiency of 9.4% at 420 nm. This work provides a novel approach to design charge-asymmetrical active site in multisite catalysts, elucidating how p-block elements influence catalytic performance in CO₂ photoreduction.