Understanding the CO₂ Activation and Hydrogenation Mechanism on MXene under Electrochemical Conditions

MXenes (MXs) are attracting growing interest as promising catalysts for CO₂ reduction reactions. However, the specific activation and reduction mechanism of CO₂ on MXs under realistic electrochemical conditions remain unclear. This study utilizes ab initio molecular dynamics simulations to unravel the kinetic processes of underlying CO₂ activation and hydrogenation under aqueous conditions with Mo₂C MX as a prototype. These findings reveal that the presence of water molecules significantly enhances the charge transfer of CO₂, facilitating its activation on MX. Notably, an insight highlights that the initial hydrogenation of *CO₂ on MX prefers to occur on oxygen rather than carbon, favoring the formation of *HOCO over *OCHO. This study proposes that the introduction of alkali metal cations including Li⁺, Na⁺, and Cs⁺ can stabilize the adsorption of CO₂ and reaction intermediates on MX via altering the interfacial water structure and hydrogen bonding network and thus effectively inhibiting the competitive hydrogen evolution reaction. Further dynamic vibrational spectra simulations shed light on the interaction between alkaline metal cations and adsorbed CO₂ molecules, which will provide a theoretical basis for the in situ detection of reactants. This work provides a deeper insight into the dynamic solid-liquid interface at the atomic level.