Surface-defect engineering of metal nanoclusters for highly efficient electrocatalytic CO₂ reduction

Defect engineering serves as a pivotal strategy for improving the performance of CO₂ electrocatalytic reduction (CO₂RR). However, understanding the structure-activity relationship between defect configurations and catalytic activity at the atomic level remains a significant challenge. This study utilized a series of structurally well-defined Au₁Ag_24+2n(SR)_18+n (where n = 0, 1, 2; SR = adamantanethiol) nanoclusters as model catalysts to systematically explore the impact of defect engineering on CO₂RR. In the Au₁Ag₂₆ nanocluster, rearrangement of the peripheral ligands creates structural defects, which increases the exposure of the active surface area. This defect engineering leads to optimal catalytic performance, achieving a Faradaic efficiency (FE) for CO of 63% at −1.0 V (vs. RHE)—nearly double that of Au₁Ag₂₄, which has an FE of 32%. In contrast, due to the surface units of Au₁Ag₂₈ being fully covered, its catalytic activity is negligible (FE_CO < 5%). By integrating comprehensive structural characterization with electrocatalytic performance analysis, we have demonstrated at the atomic level that the Ag₁S₃ motif acts as the possible catalytic active center, with catalytic performance exhibiting a direct correlation with the degree of active site exposure. This research uncovers the fundamental mechanism by which defect engineering enhances CO₂RR catalyst performance by reconstructing the coordination environment and strategically exposing active sites of cluster-based catalysts.