Cation-Coordinated Inner-Sphere CO 2 Electroreduction at Au-Water Interfaces.

Electrochemical CO 2 reduction reaction (CO 2 RR) is a promising technology for the clean energy economy. Numerous efforts have been devoted to enhancing the mechanistic understanding of CO 2 RR from both experimental and theoretical studies. Electrolyte ions are critical for the CO 2 RR; however, the role of alkali metal cations is highly controversial, and a complete free energy diagram of CO 2 RR at Au-water interfaces is still missing. Here, we provide a systematic mechanism study toward CO 2 RR via ab initio molecular dynamics simulations integrated with the slow-growth sampling (SG-AIMD) method. By using the SG-AIMD approach, we demonstrate that CO 2 RR is facile at the inner-sphere interface in the presence of K cations, which promote the CO 2 activation with the free energy barrier of only 0.66 eV. Furthermore, the competitive hydrogen evolution reaction (HER) is inhibited by the interfacial cations with the induced kinetic blockage effect, where the rate-limiting Volmer step shows a much higher energy barrier (1.27 eV). Eventually, a comprehensive free energy diagram including both kinetics and thermodynamics of the CO 2 RR to CO and the HER at the electrochemical interface is derived, which illustrates the critical role of cations on the overall performance of CO 2 electroreduction by facilitating CO 2 adsorption while suppressing the hydrogen evolution at the same time.