Highly Selective Electroreduction of CO ₂ to Formate Over Intermetallic Ag ₃ Sn Catalysts

ABSTRACT Silver–tin (Ag–Sn) composite catalysts are widely studied for the electrocatalytic CO ₂ reduction reaction (CO ₂ RR), a promising strategy to mitigate CO ₂ 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 Ag ₃ Sn, an ordered intermetallic phase, as a pivotal electrocatalyst for selective CO ₂ ‐to‐formate conversion through combined theoretical calculations and experiments. Density functional theory calculations predict that Ag ₃ Sn optimizes adsorption and stabilization of the key HCOO* intermediate via cooperative electronic and structural effects. Experimentally, the synthesized Ag ₃ Sn catalyst delivers a Faradaic efficiency of 92.3% for HCOOH at −1.0 V vs. RHE, outperforming Ag and SnO ₂ references. Control experiments further reveal that introducing excess Ag or SnO ₂ onto Ag ₃ Sn does not improve selectivity, highlighting the essential role of its intermetallic structure. In addition, Ag ₃ Sn exhibits superior formate selectivity compared with Ag/SnO ₂ interfaces in the physical mixtures of An and SnO ₂ , attributed to a hydrogen spillover‐assisted pathway. This work establishes Ag ₃ Sn as an effective phase for selective CO ₂ ‐to‐formate conversion and provides mechanistic insights to guide rational design of CO ₂ RR catalysts for targeted products.