A theoretical and experimental study on CO₂ reduction selectivity of Mo₂CT_x MXene catalysts: Influence of surface termination

Understanding the relationship between CO₂ reduction reaction (CO₂RR) performance and surface terminations of MXenes is crucial for designing effective electrocatalysts. This study explores the impact of common terminations on Mo₂CT_x using a computational hydrogen electrode (CHE) model integrated with a pseudo-microkinetic model (pseudo-MM). Unlike traditional CHE methods, CHE/pseudo-MM considers the energy differences of all steps, providing a comprehensive view of CO₂RR mechanisms while reducing computational cost generated from calculating transitional state. The electrolyte is considered as acetonitrile with 1-ethyl-3-methylimidazolium tetra-fluoroborate (EMIMBF₄) to inhibit the generation of hydrogen. Theoretical predictions reveal surface terminations dictate the selectivity of C₁ products, whose proton is provided by EMIMBF₄. The selectivity for fully –F, –O– and –OH–terminated Mo₂CT_x surfaces varies with the applied potential, as confirmed by experiments. Electrochemical CO₂RR in acetonitrile with EMIMBF₄ electrolyte confirms these predictions, showing that CH₄ outperforms CO and gradually becomes the dominant product as the applied potential increases. These findings demonstrate the qualitative accuracy of the proposed CHE/pseudo-MM for predicting CO₂RR selectivity, particularly for gaseous products, over Mo₂CT_x systems.