Oxygen-Enhanced Chemical Stability of Lithium-Mediated Electrochemical Ammonia Synthesis

Although oxygen added to nonaqueous lithium-mediatedelectrochemical ammonia synthesis (LiMEAS) enhances Faradaicefficiency, its effect on chemical stability and byproducts requiresunderstanding. Therefore, standardized high-resolution gas chromatog-raphy-mass spectrometry and nuclear magnetic resonance wereemployed. Different volatile degradation products have been qualitativelyanalyzed and quantified in tetrahydrofuran electrolyte by adding someoxygen to LiMEAS. Electrodeposited lithium and reduction/oxidation ofthe solvent on the electrodes produced organic byproducts to differentextents, depending on the oxygen concentration, and resulted in lessdecomposition products after LiMEAS with oxygen. The main organiccomponent in solid-electrolyte interphase was polytetrahydrofuran, whichdisappeared by adding an excess of oxygen (3 mol %) to LiMEAS. Thetotal number of byproducts detected was 14, 9, and 8 with oxygenconcentrations of 0, 0.8, and 3 mol %, respectively. The Faradaic efficiency and chemical stability of the LiMEAS have been greatlyimproved with addition of optimal 0.8 mol % oxygen at 20 bar total pressure.

Automated summary

In this study, the volatile degradation products in the tetrahydrofuran electrolyte of LiMEAS were qualitatively and quantitatively analyzed by adding different concentrations of oxygen. The results showed that the addition of optimal oxygen concentration can reduce the decomposition of products, improve the Faradaic efficiency and chemical stability of LiMEAS.