Electrocatalytic CO₂ Reduction Modulated by the Surface Microenvironment of Nanoclusters

Electrochemical CO₂ reduction reaction (eCO₂RR) offers a promising solution to mitigating carbon emissions by converting CO₂ into value-added chemicals. However, the catalytic activity and product selectivity of eCO₂RR are intricately dependent on the local microenvironment at the catalyst-electrolyte interface, which influences mass diffusion and surface interactions. Achieving a molecular-level understanding of this reaction mechanism is particularly challenging, as it demands precise control over catalyst structures and interfacial properties.
In this study, we report the synthesis of atomically precise 25-atom silver nanoclusters (Ag₂₅) protected by a shell of 18 thiolate ligands, with tunable surface hydrophobicity. By introducing a bulky alkyl group near the Ag₂₅ surface, the hydrophobic Ag₂₅ cluster exhibits dramatically enhanced eCO₂RR activity, achieving a CO Faradaic efficiency (FE_CO) of 90.3% and a partial CO current density (j_CO) of −240 mA cm^-2 in a gas-fed membrane electrode assembly (MEA) device at a cell potential of −3.4 V. In comparison, a hydrophilic Ag₂₅ cluster shows a lower FE_CO of 66.6%, underscoring the critical role of surface microenvironment in modulating CO₂ and water interactions.
Operando surface-enhanced infrared absorption spectroscopy (SEIRAS) and theoretical simulations provide mechanistic insights into how the ligands' hydrophobicity influences the structure of water near the catalyst surface and stabilizes the *CO intermediates, leading to enhanced eCO₂RR performance. These findings demonstrate that tailoring the local surface microenvironment of nanoclusters can significantly impact their catalytic behavior, offering a pathway to design more efficient and selective eCO₂RR catalysts.
This work highlights the importance of precisely engineering nanocluster catalysts with well-defined surface properties to address current limitations in eCO₂RR, particularly in terms of product selectivity and stability. By controlling the hydrophilic/hydrophobic balance, this approach opens new avenues for advancing CO₂ conversion technologies, with broader implications for sustainable chemical processes. The hydrophobic Ag₂₅ cluster also demonstrated excellent long-term stability, maintaining high eCO₂RR performance for over 120 hours, showcasing its potential for practical applications.