Since its verification in 2019, there have been numerous high-profile papers reporting improved efficiency of lithium-mediated electrochemical nitrogen reduction to make ammonia. However, the literature lacks any coherent investigation systematically...

The performance of the Li-mediated ammonia synthesis has progressed dramatically since its recent reintroduction. However, fundamental understanding of this reaction is slower paced, due to the many uncontrolled variables influencing it. To address this, we developed a true nonaqueous LiFePO4 reference electrode, providing both a redox anchor from which to measure potentials against and estimates of sources of energy efficiency loss. We demonstrate its stable electrochemical potential in operation using different N2- and H2-saturated electrolytes. Using this reference, we uncover the relation between partial current density and potentials. While the counter electrode potential increases linearly with current, the working electrode remains stable at lithium plating, suggesting it to be the only electrochemical step involved in this process. We also use the LiFePO4/Li+ equilibrium as a tool to probe Li-ion activity changes in situ. We hope to drive the field toward more defined systems to allow a holistic understanding of this reaction.

Since its verification in just 2019, there have been numerous high-profile papers reporting improved efficiency of the lithium-mediated electrochemical nitrogen reduction system to make ammonia. However, the literature lacks a cohesive investigation systematically linking bulk electrolyte properties to electrochemical performance and Solid Electrolyte Interphase (SEI) properties. In this study, we vary electrolyte salt concentration and observe a transition from an unstable working electrode potential to working electrode potential stability and peak in Faradaic efficiency of 7.8 ± 0.5 % at 0.6 M LiClO4. The behaviour is linked to the formation of Solvent Separated Ion Pairs in the electrolyte through Raman spectroscopy. Time of Flight Secondary Ion Mass Spectrometry and X-Ray Photoelectron Spectroscopy reveal a more inorganic, and therefore more stable, SEI layer with increasing salt concentration. A drop in Faradaic efficiency is seen at concentrations higher than 0.6 M LiClO4, which is attributed to a combination of a loss in nitrogen solubility and diffusivity as well as increased SEI conductivity as measured by Electrochemical Impedance Spectroscopy.

The lithium-mediated system catalyzes nitrogen to ammonia under ambient conditions. Herein we discover that trace amount of water as an electrolyte additive—in contrast to prior reports from the literature–can effect a dramatic improvement in the Faradaic selectivity of N 2 reduction to NH 3 . We report that an optimal water concentration of 35.9 mM and LiClO 4 salt concentration of 0.8 M allows a Faradaic efficiency up to 27.9 ± 2.5% at ambient pressure. We attribute the increase in Faradaic efficiency to the incorporation of Li 2 O in the solid electrolyte interphase, as suggested by our X-ray photoelectron spectroscopy measurements. Our results highlight the extreme sensitivity of lithium-mediated N 2 reduction to small changes in the experimental conditions.

The verification of the lithium-mediated nitrogen reduction system in 2019 has led to an explosion in the literature focussing on improving the metrics of Faradaic efficiency, stability, and activity. However,...