Promoting CO₂ Electroreduction to Hydrocarbon Products via Sulfur-Enhanced Proton Feeding in Atomically Precise...

Thiolate-protected Cu clusters with well-defined structures and stable low-coordinated Cu⁺ species exhibit remarkable potential for the CO₂RR and are ideal model catalysts for establishing structure-electrocatalytic property relationships at the atomic level. However, extant Cu clusters employed in the CO₂RR predominantly yield 2e^- products. Herein, two model Cu₄(MMI)₄ and Cu₈(MMI)₄(^tBuS)₄ clusters (MMI=2-mercapto-1-methylimidazole) are prepared to investigate the synergistic effect of Cu⁺ and adjacent S sites on the CO₂RR. Cu₄(MMI)₄ can reduce CO₂ to deep-reduced products with a 91.0 % Faradaic efficiency (including 53.7 % for CH₄) while maintaining remarkable stability. Conversely, Cu₈(MMI)₄(^tBuS)₄ shows a remarkable preference for C₂₊ products, achieving a maximum FE of 58.5 % with a C₂₊ current density of 152.1 mA⋅cm^-2. In situ XAS and ex situ XPS spectra reveal the preservation of Cu⁺ species in Cu clusters during CO₂RR, extensively enhancing the adsorption capacity of *CO intermediate. Moreover, kinetic analysis and theoretical calculations confirm that S sites facilitate H₂O dissociation into *H species, which directly participate in the protonation process on adjacent Cu sites for the protonation of *CO to *CHO. This study highlights the important role of Cu-S dual sites in Cu clusters and provides mechanistic insights into the CO₂RR pathway at the atomic level.