Deciphering the Nitrogen Activation Mechanisms on Group VIII Single Atoms at MoS₂

The activation of nitrogen (N₂) is vital for sustainable ammonia production and nitrogen fixation technologies. This study employs density functional theory (DFT) to investigate the nitrogen activation and reduction capabilities of Group VIII single-atom catalysts anchored on MoS₂. Among these, osmium anchored on MoS₂ (Os@MoS₂) emerged as the most promising catalyst, exhibiting the highest N₂ activation and the lowest nitrogen reduction reaction (NRR) overpotential (0.624 V). A pronounced "electron drift" effect was observed for Os@MoS₂, leading to significant charge redistribution that weakens the N ≡ N triple bond, facilitating its activation. The N-N dissociation energy barrier at the *N-NH₂ intermediate was calculated to be only 0.82 eV, confirming Os@MoS₂'s superior catalytic efficiency. Detailed analyses, including electrostatic potential maps, electron localization functions, spin density, and charge transfer, revealed the pivotal role of orbital interactions in driving N₂ activation. Interestingly, the trends in adsorbed N₂ bond energies and NRR overpotentials showed a consistent diagonal pattern across the Group VIII catalysts, emphasizing the importance of electronic and geometric factors. This work offers valuable insights into nitrogen activation mechanisms and provides a framework for designing efficient catalysts, highlighting Os@MoS₂'s potential in sustainable ammonia synthesis.