Molecular understanding of the critical role of alkali metal cations in initiating CO2 electroreduction on Cu(100) surface

Molecular understanding of the solid–liquid interface is challenging but essential to elucidate the role of the environment on the kinetics of electrochemical reactions. Alkali metal cations (M + ), as a vital component at the interface, are found to be necessary for the initiation of carbon dioxide reduction reaction (CO 2 RR) on coinage metals, and the activity and selectivity of CO 2 RR could be further enhanced with the cation changing from Li + to Cs + , while the underlying mechanisms are not well understood. Herein, using ab initio molecular dynamics simulations with explicit solvation and enhanced sampling methods, we systematically investigate the role of M + in CO 2 RR on Cu surface. A monotonically decreasing CO 2 activation barrier is obtained from Li + to Cs + , which is attributed to the different coordination abilities of M + with *CO 2 . Furthermore, we show that the competing hydrogen evolution reaction must be considered simultaneously to understand the crucial role of alkali metal cations in CO 2 RR on Cu surfaces, where H + is repelled from the interface and constrained by M + . Our results provide significant insights into the design of electrochemical environments and highlight the importance of explicitly including the solvation and competing reactions in theoretical simulations of CO 2 RR. Alkali metal cations affect CO 2 electroreduction performance. Here, the authors provide a comprehensive molecular understanding of the alkali metal cation effects on both CO 2 activation and competing hydrogen evolution based on explicit solvation models.