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

Abstract

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 (CO₂RR) on coinage metals, and the activity and selectivity of CO₂RR 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 CO₂RR on Cu surface. A monotonically decreasing CO₂ activation barrier is obtained from Li⁺ to Cs⁺, which is attributed to the different coordination abilities of M⁺ with *CO₂. Furthermore, we show that the competing hydrogen evolution reaction must be considered simultaneously to understand the crucial role of alkali metal cations in CO₂RR 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 CO₂RR.