Termination effects of single-atom decorated v-Mo₂CT_x MXene for the electrochemical nitrogen reduction reaction

The lack of the green, economical and high-efficient catalysts restrict the development of electrochemical nitrogen reduction reaction (NRR). By means of density functional theory (DFT) calculations, we have systematically investigated the NRR catalytic performance of single atoms decorated v-Mo₂CT₂ (T = O, F, OH, Cl, and Li) MXene (TM@v-Mo₂CT₂). Our calculation results reveal the introduction of single atom can significantly improve the NRR activity and selectivity on v-Mo₂CO₂, and Ir@v-Mo₂CO₂ system possesses the lowest limiting potential of only -0.33 V among all studied systems. The termination effects of TM@v-Mo₂CT₂ are further discussed and a descriptor of the adsorption energy of *NNH species (ΔE(*NNH)) is proposed to establish the relationship with NRR limiting potential (U_L(NRR)), in which a moderate (ΔE(*NNH)) is required for high NRR activity. Moreover, a good linear relationship between the ΔE(*NNH) and the excess electrons on Ir atom shows that different ΔE(*NNH) originates from the difference of valence state of Ir atom, which is due to the change of coordination environment. Importantly, the synergistic effects of Ir atom and the surface O-terminations during the first hydrogenation step lead to a promoted NRR performance. Our study might provide new possibilities for rational design of cost-effective MXene-based NRR electrocatalysts.