Nitrogen Electroreduction on Borophene-Supported Atomic and Diatomic Transition Metals: Stability, Activity and Selectivity Improvements via Defect-Engineering.

The present work investigated the binding of atomically dispersed transition metals to the perfect and single/double vacancy (SV/DV)-containing defective β 12 -borophenes and the catalytic performance of those corresponding single-atom catalysts (SACs) and diatomic catalysts (DACs) for nitrogen reduction reaction (NRR) by means of density functional theory calculations. Although previous theoretical studies proposed that the inherent hexagon hole of the defect-free β 12 -borophene is capable of anchoring single metal atom for NRR, calculations suggested that the interaction between borophene and doped metal is not strong enough to avoid metal aggregation. For the defective β 12 -borophene with SV, even though the single metal could be stabilized in an 8-membered ring, it was found that the SAC was still ineffective for NRR because of the competitive hydrogen evolution process. Regarding the DV-containing β 12 -borophene, a defective configuration with an unexpected 11-membered hole was proved as the most stable structure, which possessed a very similar average atomic energy (6.25 eV atom -1 ) compared to that of the pristine β 12 sheet (6.26 eV atom -1 ). Two metal atoms could be encapsulated into the confined space of the B 11 ring. Compared to SACs, those corresponding DACs were more active for N 2 fixation and hydrogenation, and the hydrogen evolution reaction could be passivated, attributing to the synergistic effect of dual metal centres. Among all candidates, the V 2 /β 12 -DV was predicted as the most promising catalyst for NRR, with the limiting potential of as low as -0.15 V.