Modulating *OCHO Adsorption Configuration on a Reconstructed Ag₃Sn Quantum Dots/S–Sn Heterostructure for Selective CO₂-to-Formate Conversion

Electrochemical CO₂ reduction to formate offers a promising route for sustainable chemical synthesis, yet achieving high selectivity and activity remains challenging due to the inefficient adsorption of key reaction intermediates. Here, an Ag₃Sn alloy quantum dots-modified S–doped Sn (Ag₃Sn AQD/S─Sn) heterojunction catalyst is constructed using a galvanic replacement strategy followed by in situ reconstruction. This unique architecture creates abundant interfacial sites that form an integrated dual-site configuration. Combined ex situ/in situ characterizations and theoretical calculations reveal that this configuration stabilizes the bidentate adsorption of the critical *OCHO intermediate, effectively lowering the energy barrier for its conversion. Consequently, the Ag₃Sn AQD/S─Sn catalyst exhibits an enhanced Faradaic efficiency (FE) for formate of 91.8% (compared to 59.1% for S─Sn catalyst). Remarkably, in a flow cell, it achieves a high formate partial current density of –226.3 mA cm⁻² (formate FE of 88.9 ± 1.6%) and a production rate of 4225.2 µmol cm⁻² h⁻¹, along with stable operation exceeding 60 h at –200 mA cm⁻². This work highlights the design of interfacial dual-site configurations as an effective strategy for steering intermediate adsorption toward selective CO₂ conversion.