MXene termination and stacking bias on the reverse water gas shift reaction catalysis

Pristine Mo₂C MXene has been recently highlighted as a highly active and robust catalyst for the reverse water gas shift (RWGS) reaction. Here, first-principles calculations based on density functional theory (DFT) coupled with mean-field microkinetic (MKM) simulations are performed to investigate the effects of the atomic layer stacking and the surface functionalization with oxo groups on the catalyst performance. The calculated data show that ABA stacked MXene has a reactivity higher than the corresponding ABC counterpart. Moreover, a ²/₃ surface monolayer oxygen coverage on both stackings (i.e., Mo₂CO_4/3 MXene) enhances the overall reactivity compared with their pristine Mo₂C counterparts. The reactivity enhancement is small for the more stable ABA-stacked model, with a CO gas production aligned with experimental reports. However, the partial O-surface termination in the MXene with ABC stacking offers a more enhanced reactivity, supported by the higher CO gas production for the Mo₂C MXene models here considered. Thus, the MXene stacking and its functionalization are key aspects affecting the performance of the Mo₂C MXene for the RGWS reaction, which must be considered for realistic catalytic applications of MXenes.