Electronic Descriptor to Identify the Activity of SACs for E-NRR and Effect of BF₃ as Electrolyte Ion

Electrochemical nitrogen reduction reaction (e-NRR) is an eco-friendly alternative approach to generate ammonia under ambient conditions, with very low power supply. But, developing of an efficient catalyst by suppressing parallel hydrogen evolution reaction as well as avoiding the catalysts poisoning either by hydrogen or electrolyte ion is an open question. So, in order to screen the single atom catalysts (SACs) for the e-NRR, we proposed a descriptor-based approach using density functional theory (DFT) based calculations. We investigated total 24 different SACs of types TM-Pc, TM-N₃C₁, TM-N₂C₂, TM-NC₃ and TM-N₄, considering transition metal (TM). We have considered mainly BF₃ ion to understand the role of electrolyte and extended the study for four more electrolyte ions, Cl, ClO₄, SO₄, OH. Herein, to predict catalytic activity for a given catalyst we have tested 16 different electronic parameters. Out of those, electronic parameter d_xz↓ occupancy, identified as electronic descriptor, is showing an excellent linear correlation with catalytic activity (R²=0.86). Furthermore, the selectivity of e-NRR over HER is defined by using an energy parameter ▵G_*H-▵G_*NNH. Further, the electronic descriptor (d_xz↓ occupancy) can be used to predict promising catalysts for e-NRR, thus reducing the efforts on designing future single atom catalysts (SACs).