Nitrogen fixation using metallic lithium nanoparticles formed by electrospray deposition

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 h^-1 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.