Abstract: Electrocatalytic nitrogen reduction reaction (NRR) is regarded as a promising route for sustainable ammonia synthesis, but developing highly active and selective catalysts remains a critical challenge. In this work, the density functional theory calculations were performed to investigate the NRR performance of Mo-adsorbed B₂N, B₃N and B₄N monolayers. The strong interaction between Mo and its substrate ensures the good stability, as reflected by the binding energies of -8.39, -5.91 and -6.75 eV for Mo-adsorbed B₂N, B₃N and B₄N monolayers, respectively. The adsorbed Mo sites are able to activate the N₂ molecule, elongating the N≡N bond length from 1.108 Å in the gas phase to 1.128, 1.132 and 1.132 Å on Mo-B₂N, Mo-B₃N and Mo-B₄N, respectively. Free energy profile analysis reveals that the thermodynamic barriers are 1.21, 1.07 and 0.61 eV for Mo-B₂N, Mo-B₃N and Mo-B₄N, with Mo-B₄N exhibiting the highest activity. This trend clearly demonstrates that the Mo reactivity is well-tuned by its coordination. Furthermore, the electronic structure analysis shows a relation between the strength of N≡N bond and the thermodynamic energy, where a weaker strength of N≡N bond indicates a better NRR activity. Mo-B₄N material also exhibits a high thermodynamic stability, as reflected by the robustness of the structural rigidity wherein no structural collage is observed under the room temperature of 300 K. Therefore, Mo-B₄N is expected to be an active and durable catalyst fot the NRR. This study provides theoretical guidance for the design of NRR electrocatalysts and proposes viable candidate systems for experimental synthesis.

Key words: nitrogen reduction reaction, density functional theory, single-atom catalysis, nitrogen reduction reaction