Modulating Activity and Selectivity of CO2 Electroreductions at Au-Water Interfaces via Tuning Local Cation Concentration

The mechanistic understanding of CO2 reduction reaction (CO2RR) under electrochemical conditions is crucial to modulate the overall catalytic performance. While electrolyte ions have received considerable attention, it remains unclear how cation modulates CO2RR and competitive hydrogen evolution reaction (HER) at electrode-electrolyte interfaces. Herein, by tuning the cation concentration (K+) at Au-water interfaces, both CO2 activation and Volmer step are studied involving the critical first electron transfer during CO2RR and HER, respectively, via the slow-growth sampling approach integrated ab initio molecular dynamics simulations. Our results demonstrate that the high local metal cation concentration facilitates CO2RR via the direct coordination between cations and key intermediates but inhibits HER due to the destroyed connectivity of hydrogen bond network in the electric double layer, thus contributing to both high activity and selectivity of CO2RR. These findings highlight the critical role of alkali metal cations in modulating interfacial reaction kinetics.