Effect of Temperature on Faradaic Efficiency and SEI Formation in Lithium Mediated Nitrogen Reduction

Lithium-mediated nitrogen reduction (Li-N2R) can be distributed and powered by renewable energy, making it a sustainable ammonia production alternative to the Haber Bosch process. While Haber Bosch is responsible for 1.3% of CO2 emissions yearly and requires centralized facilities with high temperatures and pressures, Li-N2R works at near-ambient conditions and therefore allows for decentralized production. 1 First, lithium (Li + ) ions electroplate as lithium metal on the working electrode. Second, the deposited lithium reacts with N 2 gas to form lithium nitride (Li 3 N). Lastly, Li 3 N reacts with a proton source to form ammonia (NH 3 ) (Figure Right). During Li-N2R, the NH 3 selectivity is controlled through the mass transport of N 2 , Li + , and protons to the working electrode electrode (WE). The transport of these species is limited by the solid electrolyte interface (SEI), a passivation layer formed on top of the WE. 2 The thickness and ratio of organic and inorganic species in the SEI change at different cycling temperatures, thus affecting the rates of transport between charge and uncharged species traveling to and from the electrode. Here, we study the impacts of temperature on FE and SEI composition in 1M LiBF 4 in both diglyme (DG) and tetrahydrofuran (THF) with a 1v% ethanol (EtOH) proton source (Figure Left). Using ion chromatography (IC), nuclear magnetic resonance (NMR), and inductively coupled plasma mass spectrometry (ICP-MS) on the SEI dissolved in D 2 O, we quantify the SEI species formed at different cycling temperatures. Our correlation of temperature and SEI compositions to FE provide opportunities to engineer the SEI for improved Li-N2R FE and stability. 1 J. W. Erisman et al., Nat. Geosci 2008. 1, 636–639 2 K. Steinberg et al., Nat.