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.