Nitrogenase Inspired Nitrogen Reduction on Mo/Fe-Modified Subunene: A Computational Exploration of Bio-Mimetic 2D Catalysis

The development of bioinspired catalysts that mimic the nitrogenase enzyme has attracted significant attention for sustainable ammonia synthesis under ambient conditions. In this work, density functional theory (DFT) calculations were employed to design Fe- and Mo-decorated subunene, a newly proposed two-dimensional C–S framework that replicates the Fe–Mo cofactor environment through Fe–S and Mo–S coordination. The resulting single-atom catalysts (SACs) exhibit high structural stability and strong affinity toward molecular nitrogen adsorption. Mo-anchored subunene demonstrates markedly greater N₂ activation relative to its Fe analogue, facilitated by enhanced charge transfer and π-backdonation that significantly weakens the N≡N triple bond. Comprehensive analysis, including electronic structure characterization and Gibbs free-energy profiles, reveals that Mo-subunene follows a distal reduction pathway with an exceptionally low overpotential of 0.04 V, while Fe-subunene favors an alternative NRR mechanism with a higher limiting potential of 0.59 V. The well-balanced stabilization of NRR intermediates on the Mo site underpins its superior catalytic performance. Importantly, both Fe- and Mo-decorated subunene systems exhibit high selectivity toward N₂ reduction without susceptibility to the competing hydrogen evolution reaction. These findings establish subunene as a robust and efficient platform for mimicking enzymatic N₂ fixation and provide new insights into the design of sulfur-coordinated single-atom catalysts for electrochemical ammonia synthesis.