Dynamic Organic-Metal Interfaces Control CO2 Reduction Pathways via Water Regulated Thiol SAM Ordering

Lack of precise control over interfacial microenvironments limits the selectivity of Cu-based catalysts for the electrochemical CO2 reduction reaction (CO2RR). Here, we engineer an organic-metal interface by assembling a 1-octanethiol self-assembled monolayer (SAM) on Cu surfaces, enabling modulation of reaction pathways and inducing a pronounced selectivity shift from ethanol to methane. In situ infrared spectroscopy combined with hydrogen evolution kinetics reveals that the thiol-modified interface regulates the competitive kinetics of *CO and *H intermediates in a potential-dependent manner, which correlates with a structural transition of the SAM from a disordered to an ordered state as identified by sum frequency generation spectroscopy. DFT and AIMD simulations suggest that a disordered and mobile interface promotes high *CO coverage and C-C coupling toward ethanol production, whereas an ordered, water-stabilized SAM suppresses surface mobility, limits *CO coverage, and promotes hydrogenation pathways to methane. Overall, this work identifies SAM ordering-regulated interfacial mobility as a key descriptor linking interfacial structure, *CO coverage, and reaction selectivity, providing a general strategy for tuning CO2RR pathways via dynamic organic-metal interfaces.