Modulating Activity and Selectivity of CO2 Electroreductions at Au–Water Interfaces via Engineering Local Cation Condition

The mechanistic understanding of the CO2 reduction reaction (CO2RR) under electrochemical conditions is crucial for optimizing the overall catalytic performance. While electrolyte ions have received considerable attention, it remains unclear how the condition of interfacial cations modulates the CO2RR and the competitive hydrogen evolution reaction (HER) at the electrode-electrolyte interfaces. Herein, we explore the CO2 activation and Volmer step representing the critical first electron transfer during the CO2RR and HER, respectively. This investigation involves manipulating the cation identity (K+, Li+, and H+) and concentration at Au-water interfaces, which is carried out via the slow-growth sampling approach integrated with ab initio molecular dynamics simulations. Our results demonstrate that the high local alkali metal cation (AM+) concentration facilitates the CO2RR following the order of 2K+ > 1K+ > 2Li+ > 1Li+ > 0AM+, and the highly promoted CO2 activation kinetics originate from the short-range coordination between alkali metal cations and reaction intermediates. However, the interfacial HER behaves very differently with the kinetic order of 1Li+ > 0AM+ > 1K+ > 2Li+ > 2K+, closely related to the interfacial water structures, which are affected by both cation identity and local concentrations. Overall, the activity and selectivity of the CO2RR at the Au-water interface can be enhanced by increasing the local cation concentration (K+ > Li+). These findings highlight the critical roles of alkali metal cations and reaction microenvironments in modulating interfacial reaction kinetics.