Specific Adsorption of Alkaline Cations Enhances CO-CO Coupling in CO Electroreduction.

Electrolyte alkaline cations can significantly modulate the reaction selectivity of electrochemical CO reduction (eCOR), enhancing the yield of the valuable multicarbon (C) chemical feedstocks. However, the mechanism underlying this cation effect on the C-C coupling remains unclear. Herein, by performing constant-potential AIMD simulations, we studied the dynamic behavior of interfacial K ions over Cu surfaces during C-C coupling and the origin of the cation effect. We showed that the specific adsorption of K readily occurs at the surface sites adjacent to the *CO intermediates on the Cu surfaces. Furthermore, this specific adsorption of K during *CO-*CO coupling is more important than quasi-specific adsorption for enhancing coupling kinetics, reducing the coupling barriers by approximately 0.20 eV. Electronic structure analysis revealed that charge redistribution occurs between the specifically adsorbed K, *CO, and Cu sites, and this can account for the reduced barriers. In addition, we identified excellent *CO-*CO coupling selectivity on Cu(100) with K ions. Experimental results show that suppressing surface K-specific adsorption using the surfactant cetyltrimethylammonium bromide (CTAB) significantly decreases the Faradaic efficiency for C products from 41.1% to 4.3%, consistent with our computational findings. This study provides crucial insights for improving the selectivity toward C products by rationally tuning interfacial cation adsorption during eCOR. Specifically, C-C coupling can be enhanced by promoting K-specific adsorption, for example, by confining K within a coated layer or using pulsed negative potentials.