Nitrogen fixation using metallic lithium nanoparticles formed by electrospray deposition

Chemical Science

EDGE ARTICLE

Nitrogen fixation using metallic lithium nanoparticles formed by electrospray deposition

Multiphase reduction of ambient dinitrogen 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 is formed and lithium is regenerated from the hydrolysis of transient lithium nitride, 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 two point nine seven plus or minus zero point three six micrograms per hour of ammonia was produced by a single spray source when using pure dinitrogen 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 dinitrogen to produce ammonia. The mixed lithium metal nanoparticles were characterized with scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy, and electron energy loss spectroscopy. This ammonia synthesis has implications for the formation of nitrogenous compounds in environmental, prebiotic, and traditional synthetic contexts.