Multiphase reduction of ambient dinitrogen (N₂) was observed during the deposition of charged or uncharged aqueous microdroplets containing a lithium salt pre-catalyst onto conducting or inert surfaces to yield mixed lithium nanoparticles. We propose that this method leverages the high electric fields and partial solvation of ions at the gas-water-solid interface to enhance reaction rates and perform normally moisture-sensitive chemistry in aqueous droplets. Ammonia (NH3) is formed and Li+ is regenerated from the hydrolysis of transient lithium nitride Li3N, constituting a complete catalytic cycle. The ammonia is captured in situ using formaldehyde to yield hexamethylenetetramine, a solid nitrogenous fuel. By measuring product formation with mass spectrometry, it was determined that 2.97 ± 0.36 μg/hr of NH3 was produced by a single spray source when using pure N2 sheath gas and an applied potential, though microdroplets alone appear a sufficient source of electrons in cases where an external potential is not applied; air is also an adequate source of N2 to produce NH3. The mixed lithium metal nanoparticles were characterized with (S)TEM, EDS, and EELS. This ammonia synthesis has implications for the formation of nitrogenous compounds in environmental, prebiotic, and traditional synthetic contexts.
