Ag1+ incorporation via a Zr4+-anchored metalloligand: fine-tuning catalytic Ag sites in Zr/Ag bimetallic clusters for enhanced eCO2RR-to-CO activity

Abstract

Attaining meticulous dominion over the binding milieu of catalytic metal sites remains an indispensable pursuit to tailor product selectivity and elevate catalytic activity. By harnessing the distinctive attributes of a Zr⁴⁺-anchored thiacalix[4]arene (TC4A) metalloligand, we have pioneered a methodology for incorporating catalytic Ag¹⁺ sites, resulting in the first Zr–Ag bimetallic cluster, Zr₂Ag₇, which unveils a dualistic configuration embodying twin {ZrAg₃(TC4A)₂} substructures linked by an {AgSal} moiety. This cluster unveils a trinity of discrete Ag sites: a pair ensconced within {ZrAg₃(TC4A)₂} subunits and one located between two units. Expanding the purview, we have also crafted ZrAg₃ and Zr₂Ag₂ clusters, meticulously mimicking the two Ag site environment inherent in the {ZrAg₃(TC4A)₂} monomer. The distinct structural profiles of Zr₂Ag₇, ZrAg₃, and Zr₂Ag provide an exquisite foundation for a precise comparative appraisal of catalytic prowess across three Ag sites intrinsic to Zr₂Ag₇. Remarkably, Zr₂Ag₇ eclipses its counterparts in the electroreduction of CO₂, culminating in a CO faradaic efficiency (FE_CO) of 90.23% at −0.9 V. This achievement markedly surpasses the performance metrics of ZrAg₃ (FE_CO: 55.45% at −1.0 V) and Zr₂Ag₂ (FE_CO: 13.09% at −1.0 V). Utilizing in situ ATR-FTIR, we can observe reaction intermediates on the Ag sites. To unveil underlying mechanisms, we employ density functional theory (DFT) calculations to determine changes in free energy accompanying each elementary step throughout the conversion of CO₂ to CO. Our findings reveal the exceptional proficiency of the bridged-Ag site that interconnects paired {ZrAg₃(TC4A)₂} units, skillfully stabilizing *COOH intermediates, surpassing the stabilization efficacy of the other Ag sites located elsewhere. The invaluable insights gleaned from this pioneering endeavor lay a novel course for the design of exceptionally efficient catalysts tailored for CO₂ reduction reactions, emphatically underscoring novel vistas this research unshrouds.