Enzyme-Inspired Ligand Engineering of Gold Nanoclusters for Electrocatalytic Microenvironment Manipulation

Natural enzymes intricately regulate substrate accessibility through specific amino acid sequences and folded structures at their active sites. Achieving such precise control over the microenvironment has proven to be challenging in nanocatalysis, especially in the realm of ligand-stabilized metal nanoparticles. Here, we use atomically precise metal nanoclusters (NCs) as model catalysts to demonstrate an effective ligand engineering strategy to control the local concentration of CO₂ on the surface of gold (Au) NCs during electrocatalytic CO₂ reduction reactions (CO₂RR). The precise incorporation of two 2-thiouracil-5-carboxylic acid (TCA) ligands within the pocket-like cavity of [Au₂₅(pMBA)₁₈]^- NCs (pMBA = para-mercaptobenzoic acid) leads to a substantial acceleration in the reaction kinetics of CO₂RR. This enhancement is attributed to a more favorable microenvironment in proximity to the active site for CO₂, facilitated by supramolecular interactions between the nucleophilic N^δ- of the pyrimidine ring of the TCA ligand and the electrophilic C^δ+ of CO₂. A comprehensive investigation employing absorption spectroscopy, mass spectrometry, isotopic labeling measurements, electrochemical analyses, and quantum chemical computation highlights the pivotal role of local CO₂ enrichment in enhancing the activity and selectivity of TCA-modified Au₂₅ NCs for CO₂RR. Notably, a high Faradaic efficiency of 98.6% toward CO has been achieved. The surface engineering approach and catalytic fundamentals elucidated in this study provide a systematic foundation for the molecular-level design of metal-based electrocatalysts.