Unravelling the effects of interactions between interfacial water and atomic metal sites for CO₂ electroreduction to CO and syngas

In the electrochemical CO₂ reduction reaction, the interactions between various active sites and interfacial water influence the activation and reaction kinetics of water and CO₂ reactants, leading to differences in product distribution. However, detailed mechanisms still remain unclear. Herein, we develop single-atom catalysts (SACs) featuring isolated single-atom Ni and Co sites, as well as a dual single-atom catalyst (DSAC) consisting of ensembles of Ni and Co single atoms, to systematically investigate the influences of the interactions between single-atom sites and interfacial water for CO₂ electroreduction to CO and syngas. Combined electrochemical and in-situ spectroscopic studies reveal that Ni sites selectively convert CO₂ to CO, while Co sites promote the hydrogen evolution reaction, due to their distinct interactions with interfacial water that modify local hydrogen-bond network rigidity and reaction kinetics. At industrial current densities (50 to 300 mA cm⁻²), Ni SAC achieves ∼100 % CO Faradaic efficiency, whereas Co SAC produces syngas (CO/H₂ ≈ 0.5). In Ni-Co DSAC, synergistic regulation tunes the CO/H₂ ratio to ∼2. This work highlights the critical role of site-specific water interactions in steering selectivity and provides guidance for designing catalysts for multi-product electrocatalysis.