Multistep screening of transition-metal-based homonuclear double-atom catalysts to unravel the electronic origin of their activity and selectivity challenges for nitrogen reduction†

Lack of robust catalyst design strategies for tackling the selectivity and activity challenges poses serious limitations in the development of efficient catalysts for nitrogen reduction to ammonia. The synergistic interactions in double-atom catalysts (DACs) have aroused great interest in developing promising catalytic centers for the nitrogen reduction reaction (NRR). Using a multistep screening strategy based on systematic first-principles simulations, we find that Fe₂, Co₂, and W₂ dimer species impregnated in a tetracyanoquinodimethane-based monolayer achieve suitable adsorption behaviour for the various NRR intermediates, leading to excellent activity and selectivity among the 27 DACs considered in this study for the NRR. Interestingly, our results reveal very low limiting potential values of −0.56, −0.58, and −0.53 V for Fe₂, Co₂, and W₂, respectively, compared to the experimentally reported values of −0.73 and −0.98 V for the Ru-based single-atom catalyst and Ru(0001) stepped surface. Density of states analysis indicated that the adsorption pattern of the reaction intermediates was regulated by the d-states of the DACs near the Fermi level. Correlation trends between the limiting potential and the free energy change for adsorption of different intermediates show that the free energy change for N₂ adsorption proves a suitable guidance to evaluate the NRR activity of the modelled catalysts. Further, rigorous electronic structure analysis highlighted properties such as integrated crystal orbital Hamilton populations and orbital projected density of states, and the d-band centre could be successfully used to rationalize the N₂ binding and adsorption on these catalysts. Thus, this work provides a feasible design strategy for NRR electrocatalysis based on extensive electronic structure concepts.