Theoretical Study of Electrocatalytic CO 2 Reduction Mechanism on Typical MXenes under Realistic Conditions.

MXenes are a revolutionary class of two-dimensional materials that have been recently demonstrated to exhibit promising capability of electrocatalytic CO 2 reduction reaction (CO 2 RR) in theory and experiment. In electrocatalytic reactions, the active phases, the mechanism, and the performance can be greatly influenced by electrochemical conditions such as applied electrode potential, pH, and electrolyte. Therefore, in this first-principles study, the stable surface structures of three typical MXenes (V 2 C, Mo 2 C, and Ti 3 C 2 ) with variation of electrocatalytic conditions were determined by the Pourbaix phase diagrams. Additionally, the reaction mechanism for CO 2 RR toward C 1 products was investigated based on the thermal dynamically stable phases. The computation revealed that surfaces of all three MXenes are dominated by H* termination throughout the practical CO 2 RR electrochemical condition ranges. Meanwhile, the bicarbonate ions, which serve as the major electrolyte in CO 2 RR, show thermal dynamic unfavorability to adsorb on the surfaces. Among the three types of MXenes, V 2 CH exhibits higher activity in generating CO and HCOOH through the CO 2 RR, while Mo 2 CH exhibits higher activity in producing HCHO, CH 3 OH, and CH 4 . This comprehensive study provides crucial insights into the mechanism of electrocatalytic CO 2 RR on MXenes under realistic electrochemical conditions.