Density Functional Theory Study of Single Metal Atoms Embedded into MBene for Electrocatalytic Conversion of N2 to NH3

The central theme in single-atom catalysis is to build strong interactions between the single atoms and the support for stabilization in electrocatalytic nitrogen reduction reaction (eNRR). Herein, we utilize the well-defined ab initio computations to build up the strong coupling systems between single atoms and transition metal borides (MBene) as the superior electrocatalysts for eNRR. This work addresses a series of transition metal atoms ranging from IVB to VIII subgroups in Mo vacancies of the MBene nanosheet (Mo2B2O2) and carries out a systematic screening of activities and selectivity on the eNRR process. The computational results indicate that Re and Os supported on the defective Mo2B2O2 layer possess a remarkable catalytic activity with relatively low barrier of the potential-determining step (PDS) of 0.29 and 0.32 eV, which are lower than that of the single Ru atom decorated on Mo2CO2 (0.46 eV). The implanted Re and Os atoms selectively promote the eNRR process and suppress the hydrogen evolution reaction (HER) process in the presence of oxygen vacancies. Moreover, the number of d electrons and the horizontal periods in periodic table of the elements of single atoms are proved to be related to the first protonation step of eNRR and the crucial adsorbed species *NNH. Accordingly, the binary descriptor with respect to the number of d electrons and the period is proposed to establish the relationship between the intrinsic atomic properties and catalytic capacity. This work paves the way to the electrocatalytic atomic-level mechanism of novel MBene for the reduction of N2 to NH3 at ambient conditions.