Stepwise assembly of thiacalix[4]arene-protected Ag/Ti bimetallic nanoclusters: accurate identification of catalytic Ag sites in CO 2 electroreduction.

The accurate identification of catalytic sites in heterogeneous catalysts poses a significant challenge due to the intricate nature of controlling interfacial chemistry at the molecular level. In this study, we introduce a novel strategy to address this issue by utilizing a thiacalix[4]arene (TC4A)-protected Ti-oxo core as a template for loading Ag 1+ ions, leading to the successful synthesis of a unique Ag/Ti bimetallic nanocluster denoted as Ti 8 Ag 8 . This nanocluster exhibits multiple surface-exposed Ag sites and possesses a distinctive "core-shell" structure, consisting of a {Ti 4 @Ag 8 (TC4A) 4 } core housing a {Ti 2 O 2 @Ag 4 (TC4A) 2 } motif and two {Ti@Ag 2 (TC4A)} motifs. To enable a comprehensive analysis, we also prepared a Ti 2 Ag 4 cluster with the same {Ti 2 O 2 @Ag 4 (TC4A) 2 } structure found within Ti 8 Ag 8 . The structural disparities between Ti 8 Ag 8 and Ti 2 Ag 4 provide an excellent platform for a comparison of catalytic activity at different Ag sites. Remarkably, Ti 8 Ag 8 exhibits exceptional performance in the electroreduction of CO 2 (eCO 2 RR), showcasing a CO faradaic efficiency (FE CO ) of 92.33% at -0.9 V vs. RHE, surpassing the FE CO of Ti 2 Ag 4 (69.87% at -0.9 V vs. RHE) by a significant margin. Through density functional theory (DFT) calculations, we unveil the catalytic mechanism and further discover that Ag active sites located at {Ti@Ag 2 (TC4A)} possess a higher ε d value compared to those at {Ti 2 O 2 @Ag 4 (TC4A) 2 }, enhancing the stabilization of the *COOH intermediate during the eCO 2 RR. This study provides valuable insights into the accurate identification of catalytic sites in bimetallic nanoclusters and opens up promising avenues for efficient CO 2 reduction catalyst design.