Mechanistic Insights into Ammonia Synthesis from Nitrogen and Water Microdroplets

Ammonia (NH₃), the second most produced chemical globally, is predominantly synthesized via the traditional, energy-intensive Haber-Bosch process. Increasing attention has been devoted to exploring alternative methods for NH₃ synthesis that can be driven by renewable energy and operated under mild conditions. Recently, ammonia formation from nitrogen and water microdroplets at room temperature and ambient pressure has been proposed. In this work, using ab initio molecular dynamics (AIMD) simulations, we reveal the pivotal role of hydrated electrons in microdroplets for the nitrogen reduction reaction (NRR) and propose that the associative-dissociative mechanism is the dominant pathway for nitrogen reduction at the microdroplet interface. This mechanism comprises two key steps: (i) nitrogen is reduced via an associative mechanism to form two potential intermediates, *NHNH₃ and *NH₂NH₂, and (ii) *NHNH₃ and *NH₂NH₂ undergo N-N bond cleavage to yield ammonia. We further confirm that *NH₂NH₂ acts as an intermediate in the nitrogen reduction process, which is consistent with experimental findings. Moreover, abundant species (H₂O, *OH, and *H₂O) can serve as proton sources for the NRR, and surface-adsorbed *H₂O plays a vital role in promoting the reaction.