Single atom-supported MXene: how single-atomic-site catalysts tune the high activity and selectivity of electrochemical nitrogen fixation

Abstract

A central topic for the electrocatalytic N₂ reduction reaction (ENRR) lies in the search for facile electrocatalysts under ambient conditions. Inspired by recent works on stabilizing single atoms with Ti₃C₂T_x MXene nanosheets, herein, we designed a series of single atoms supported on Ti₂CO₂ and Mo₂CO₂ MXene monolayers as efficient electrocatalysts for the ENRR by a well-defined first-principles calculation. Our calculation results revealed that single Ru or Mo atom anchored Mo₂CO₂ or Ti₂CO₂ possessed high ENRR activity, and the calculated limiting potentials of Ti₂CO₂ were more negative than those of Mo₂CO₂ due to the high conductivity of Mo₂CO₂. Moreover, N₂ can be efficiently reduced to NH₃ on Ti@Mo₂CO₂via different reaction mechanisms with a record limiting potential (−0.64 V). Furthermore, the activity and selectivity of the ENRR on Mo@Mo₂CO₂ were evaluated by comparing the Gibbs free energy of each dinitrogen and hydrogen as well as the first dinitrogen protonation and hydrogen adsorption. We found that N₂ reduction proceeds via a distal or hybrid mechanism with an overpotential down to 0.16 or 0.19 V, indicating Mo@Mo₂CO₂ as a robust electrocatalyst for the ENRR. This work opens up an exciting new avenue for the rational design of high-efficiency MXene-based nanocomposites for artificial N₂ fixation.