Effect of the solid electrolyte interphase on lithium-mediated ammonia synthesis by Cryo-electron microscopy

Lithium-mediated nitrogen reduction reaction (Li-NRR) is a promising reaction pathway to realize green ammonia production. However, there is a lack of clear understanding on how solid electrolyte interphase (SEI) membranes affects Li-NRR performance. The effects of different lithium salts on the SEI layer were investigated in this work. Among lithium tetrafluoroborate (LiBF 4 ), lithium perchlorate (LiClO 4 ), and lithium trifluoromethanesulfonate (LiOTf), LiOTf showed better ammonia synthesis performance. At 1 bar N 2 and −6 mA cm −2 current density, the faraday efficiency (FE) and ammonia production rate reached 16.94 ± 0.67 % and 3.51 ± 0.14 nmol s −1 cm −2 , respectively. Conversely, the LiBF 4 electrolyte has the lowest NH 3 selectivity and rate under identical operating conditions, which are only 2.41 ± 0.16 % and 0.50 ± 0.03 nmol s −1 cm −2 . Cryo-electron microscopy reveals the influence of SEI nanostructures and chemical properties on the performance of lithium-mediated electrochemical synthesis of ammonia. The results of Cryo-electron microscopy showed that the SEI membranes of LiOTf electrolyte exhibited a reticular structure, which was favorable for N 2 adsorption, while the SEIs of LiClO 4 and LiBF 4 electrolytes had a lamellar and irregular planar structure, respectively. Molecular dynamics (MD) simulations and density functional theory (DFT) results showed that the LiOTf electrolyte can more easily generate a stable SEI membrane on the electrode surface. These findings highlight the importance of SEI structure in enhancing the reaction process, and thus provide valuable suggestions for the development of artificial SEI with specific structure.