Specific Adsorption of Alkaline Cations Enhances CO–CO Coupling in CO₂ Electroreduction

Abstract

Electrolyte alkaline cations can significantly modulate the reaction selectivity of electrochemical CO 2 reduction (eCO 2 R), enhancing the yield of the valuable multicarbon (C 2+ ) 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 2 products from 41.1% to 4.3%, consistent with our computational findings. This study provides crucial insights for improving the selectivity toward C 2+ products by rationally tuning interfacial cation adsorption during eCO 2 R. 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.