Activity and Selectivity Modulation of CO2 Electroreductions at Au-Water Interfaces Via Tuning Localcation Concentrations

Electrochemical CO 2 reduction reaction (CO 2 RR) is a promising technique for converting the greenhouse gas CO 2 into valuable fuels and chemicals in a clean energy society. To understand the underlying electrocatalytic reaction mechanism from the atomic level, researchers are investigating the role of electrolyte ions, particularly alkali metal cations, in various electrocatalytic reactions including CO 2 RR. Despite this attention, the impact of alkali metal cations is still a topic of debate, and it remains unclear how cations affect the CO 2 RR and the competing hydrogen evolution reaction (HER). In this study, explicit cations and water solvents were added to Au-water interfacial models to simulate the pathways of CO 2 RR and HER. Two cations (K + , Li + , and/or H + ) were used in the model system to create similarly charged Au surfaces, and the local concentration of alkali metal cations (AM + ) was adjusted by replacing AM + (K + and Li + ) with H + . The first electron transfer step was considered critical in electrocatalytic reductions, so CO 2 activation and water dissociation were evaluated for CO 2 RR and HER, respectively. Ab initio molecular dynamics (AIMD) simulations with the slow-growth sampling approach (SG-AIMD) were used to simulate the corresponding reaction mechanisms, and kinetic barriers were obtained through thermodynamic integrations. With these Au-water-cations interfacial models, a systematic study was conducted to investigate the mechanism of CO 2 activation at Au-water-2AM + , Au-water-1AM + , and Au-water-0AM + interfaces. These results show that a high concentration of metal cations with 2AM + promotes CO 2 activation through short-range electrostatic interactions between cations and key intermediates. Besides CO 2 activation, this study also investigated water dissociation during the competing HER. Contrary to the promotion effect observed in CO 2 RR, local alkali metal cations were found to suppress water dissociation with a high reaction barrier (Figure 1). This can be attributed to the broken connectivity of the hydrogen bond network at Au-water-2AM + interfaces. The reaction kinetics can be improved by reducing the metal cation concentration. Notably, K + was found to have a more pronounced promotion effect than Li + on CO 2 activation, while the opposite suppression effect was observed on HER. By tuning the local alkali metal cation concentration, it is anticipated that the overall performance of CO 2 RR, including both activity and selectivity, can be engineered. Figure 1