CO2 Electroreduction to CO Over Silver Nanoclusters: The Impact of Nuclearity on Synergistic Activity Modulation

Abstract

Electrochemical reduction of CO<inf>2</inf> (eCO<inf>2</inf>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<inf>2</inf>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<inf>21</inf>(MCT)<inf>12</inf>(TPP)<inf>2</inf>]+, [Ag<inf>31</inf>(TRZ)<inf>10</inf>]2−, [Ag<inf>42</inf>(CBDT)<inf>15</inf>(TPP)<inf>4</inf>]2− (shortly, Ag<inf>21</inf>, Ag<inf>31</inf>, and Ag<inf>42</inf>, respectively), reveal that the CO Faradaic efficiency (FE<inf>CO</inf>) increases while the FE<inf>CO(max)</inf> (the maximum FE<inf>CO</inf>) 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<inf>CO(max)</inf> and maximum partial current density, j<inf>CO</inf><inf>(</inf><inf>max</inf><inf>)</inf> by ≈70 and ≈80 mV, respectively. The smallest nanocluster, Ag<inf>21</inf>, achieved a near-unity FE<inf>CO(max)</inf> of 99.6% at −0.59 V vs RHE, and a competitive eCO<inf>2</inf>R-to-CO rate, producing a j<inf>CO</inf><inf>(</inf><inf>max</inf><inf>)</inf> 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. © 2025 Elsevier B.V., All rights reserved.