Atomically Dispersed Metal Dimer Species with Selective Catalytic Activity for Nitrogen Electrochemical Reduction

The electrocatalytic nitrogen reduction reaction (NRR) is emerging as an attractive strategy for ammonia (NH3) sustainable and distributed production under ambient conditions. Owing to the unsatisfactory electrocatalyst employment, however, it is still encountering issues of low yield rate and limited efficiency, resulting from the sluggish reaction kinetics, the competing hydrogen evolution reaction and additional reaction products formation. Herein, an atomically dispersed transition metal dimer species were employed to selectively accelerate the nitrogen reduction reaction kinetics for high reduction efficiency and simultaneously alleviate the additional reaction. In this system, atomic Fe and Mo metal dimer in situ anchored on defect-rich graphene layers can realize selective electroreduction of nitrogen to ammonia by numerous FeMoN6 active sites. It exhibits higher catalytic activity than the counterpart (Fe@NG and Mo@NG) owing to a combination of ligand, geometric and synergistic effects, with a yield rate of 14.95 µg h-1 mg-1 at -0.4 V and Faradic efficiency of 41.7 % at -0.2 V, respectively. The superior performance of this atomic transition metal dimer catalysts can outperform some precious metal-based catalysts due to its excellent selectivity and high catalytic activity. The specific structure of the N-coordinated FeMo dimer was further identified to be FeMoN6 by density functional theory (DFT). The catalytic reaction pathway and mechanism were explored by density functional theory (DFT) calculations and proposed based on FeMoN6 model. The numerous existence of FeMoN6 active site can not only weakens N  N bond, but also efficiently catalyzes nitrogen reduction through the alternating pathway.