Operando -Evolved Sn ₂ S ₃ /SnO ₂ Heterojunction Promotes CO ₂ Electroreduction to Formate via Accelerated Water Dissociation

Dynamic interfacial reconstruction can fundamentally reshape the catalytic pathway of CO 2 electroreduction, yet how it regulates H 2 O participation on Sn-based catalysts remains unclear. Here we report a precursor SnS 2 /SnO 2 heterostructure that evolves operando into an active Sn 2 S 3 /SnO 2 heterojunction during CO 2 electroreduction. The reconstructed catalyst achieves a formate Faradaic efficiency of 90.9% with a formate partial current density of 35.2 mA·cm –2 at −1.0 V vs RHE and maintains FE formate above 85% for 70 h. In situ Raman spectroscopy reveals the formation of the active Sn 2 S 3 /SnO 2 interface under the working conditions. In situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy identifies enhanced *OCHO formation and distinct interfacial H 2 O restructuring of the evolved heterojunction. Microkinetic analysis indicates that the S-containing interface accelerates H 2 O dissociation, improves the hydrogen supply for proton-coupled *OCHO formation, and thereby drives selective CO 2 -to-formate conversion. This work highlights operando heterojunction evolution as an effective strategy to couple H 2 O activation with selective CO 2 hydrogenation.