Highly Selective Electroreduction of CO₂ to Formate Over Intermetallic Ag₃Sn Catalysts

Silver–tin (Ag–Sn) composite catalysts are widely studied for the electrocatalytic CO₂ reduction reaction (CO₂RR), a promising strategy to mitigate CO₂ emissions while producing value-added chemicals such as formate. Previous studies show that Ag–Sn heterostructures or core–shell architectures can tune the intrinsic selectivity of Ag, shifting its preference from CO toward formate. However, the precise Ag–Sn active sites responsible for enhanced formate selectivity remain unclear. Herein, we identify Ag₃Sn, an ordered intermetallic phase, as a pivotal electrocatalyst for selective CO₂-to-formate conversion through combined theoretical calculations and experiments. Density functional theory calculations predict that Ag₃Sn optimizes adsorption and stabilization of the key HCOO* intermediate via cooperative electronic and structural effects. Experimentally, the synthesized Ag₃Sn catalyst delivers a Faradaic efficiency of 92.3% for HCOOH at −1.0 V vs. RHE, outperforming Ag and SnO₂ references. Control experiments further reveal that introducing excess Ag or SnO₂ onto Ag₃Sn does not improve selectivity, highlighting the essential role of its intermetallic structure. In addition, Ag₃Sn exhibits superior formate selectivity compared with Ag/SnO₂ interfaces in the physical mixtures of An and SnO₂, attributed to a hydrogen spillover-assisted pathway. This work establishes Ag₃Sn as an effective phase for selective CO₂-to-formate conversion and provides mechanistic insights to guide rational design of CO₂RR catalysts for targeted products.