Two-Dimensional Single-Atom Catalyst TM₃(HAB)₂ Monolayers for Electrocatalytic Dinitrogen Reduction Using Hierarchical High-Throughput Screening

As an environmentally friendly and sustainable strategy to produce ammonia, the electrocatalytic nitrogen reduction reaction (eNRR) is facing the challenge of low conversion rates and high overpotential, to solve which efficient catalysts are urgently needed. Here, a new class of two-dimensional metal–organic layers (MOLs) TM3(HAB)2 (TM = 30 transition metals; HAB = hexaaminobenzene) were evaluated via a three-step high-throughput screening combined with the spin-polarized density functional theory (DFT) method to obtain eligible TM3(HAB)2 catalysts embedded with transition metal atoms from 3d to 5d. Our investigation revealed that Nb3(HAB)2, Mo3(HAB)2, and Tc3(HAB)2 are eligible NRR candidates, among which Tc3(HAB)2 possesses the best catalytic performance with a lowest onset potential of −0.63 V via both distal and alternating pathways and an ultralow NH3 desorption free energy of 0.22 eV. Furthermore, the band structures of three catalysts show their nice conductivity. The corresponding projected density of states (PDOS) illustrate that high catalytic activity can be ascribed to apparent orbital hybridization and charge transfer between catalysts and adsorbed N2. Later, stability and selectivity of all three candidates were computed, Tc3(HAB)2 and Nb3(HAB)2 catalysts are proved to facilitate dinitrogen reduction and exhibit good stability and high selectivity, yet NRR on the Mo3(HAB)2 catalyst is inhibited by hydrogen evolution reaction (HER). Based on the abovementioned studies, we concluded that Tc3(HAB)2 and Nb3(HAB)2 monolayers are promising catalysts for nitrogen fixation. We expect this work to fill the gap of exploring more eligible single-atom catalysts (SACs) anchored with transition metal atoms on MOLs for NRR.