CO 2 Electroreduction to CO Over Silver Nanoclusters: The Impact of Nuclearity on Synergistic Activity Modulation

Abstract Electrochemical reduction of CO 2 (eCO 2 R) powered by renewable energy holds the potential to produce sustainable platform chemicals and decarbonize the hard‐to‐abate sectors. Herein, the structure‐activity correlation of atomically precise silver nanoclusters (NCs) in eCO 2 R to carbon monoxide (CO) is studied, elucidating the effect of the nuclearity of metal core and the electronic nature of the ligands. Electrocatalytic studies on Ag NCs, [Ag 21 (MCT) 12 (TPP) 2 ] + , [Ag 31 (TRZ) 10 ] 2− , [Ag 42 (CBDT) 15 (TPP) 4 ] 2− (shortly, Ag 21 , Ag 31 , and Ag 42 , respectively), reveal that the CO Faradaic efficiency (FE CO ) increases while the FE CO(max) (the maximum FE CO ) moves to higher positive potentials upon decreasing the nuclearity of these Ag NCs, almost in a quantitative correlation. Notably, every ≈ten Ag atoms variation in the cluster shifts the potentials for FE CO(max) and maximum partial current density, j CO ( max ) by ≈70 and ≈80 mV, respectively. The smallest nanocluster, Ag 21 , achieved a near‐unity FE CO(max) of 99.6% at −0.59 V vs RHE, and a competitive eCO 2 R‐to‐CO rate, producing a j CO ( max ) of 148 mA cm −2 at −0.7 V vs RHE. First principle calculations reveal that decreasing the atomicity in Ag NCs reduces the activation energy barriers for the 2e − reduction pathway due to the modulation of surface charge distribution and the electronic density of states of the active Ag sites.