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

MXenes are attracting growing interest as promising catalysts for CO2 reduction reactions. However, the specific activation and reduction mechanism of CO2 on MXenes under realistic electrochemical conditions remains unclear. In this study, we utilize ab initio molecular dynamics simulations to unravel the kinetic processes of underlying CO2 activation and hydrogenation under aqueous conditions with Mo2C MXene as a prototype. Our findings reveal that the presence of water molecules significantly enhances the charge transfer of CO2, facilitating its activation on MXene. Notably, we highlight an insight that the initial hydrogenation of *CO2 on MXene prefers to occur on oxygen rather than carbon, favoring the formation of *HOCO over *OCHO. We proposed that the introduction of alkali metal cations including Li+, Na+, and Cs+ can stabilize the adsorption of CO2 and reaction intermediates on MXene via altering the interfacial water structure and hydrogen bonding network, and thus effectively inhibiting the competitive hydrogen evolution reaction (HER). 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. Our work provides a deeper insight into the dynamic solid-liquid interface at the atomic level.