Low-Volatility and High-Stability Solvents for Stabilizing Lithium-Mediated Electrochemical Ammonia Synthesis

Lithium-mediated electrochemical ammonia synthesis (Li-MEAS) is a promising green route for ammonia production. However, the widely used tetrahydrofuran (THF)-based electrolytes exhibit intrinsic drawbacks of high volatility and poor anodic stability, which necessitate frequent and excessive electrolyte replenishment, further resulting in increased operating costs and environmental risks. Therefore, developing electrolytes with low/nonvolatility and high electrochemical stability is critical to enable lean-electrolyte operation of Li-MEAS systems. In this work, we systematically evaluated ethylene carbonate (EC)-, propylene carbonate (PC)-, and 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF 4 ])-based electrolytes for Li-MEAS. All three solvents show significantly lower volatility and higher anodic stability than the THF-based electrolyte. When employed in a Li-MEAS reactor, EC-based and PC-based electrolytes achieve Faradaic efficiencies (FE) of 83.05 and 74.76%, respectively, which are comparable to that of the THF-based benchmark electrolyte (85.91%). Owing to their low volatility, high electrochemical stability, and favorable solid electrolyte interphase (SEI) formation capability, the cyclic carbonate-based electrolytes enable stable Li-MEAS operation for over 40 min under lean-electrolyte conditions. In contrast, the [EMIM][BF 4 ]-based electrolyte yields ammonia primarily from cation degradation rather than selective N 2 reduction under the tested conditions, leading to false positive results. This study confirms the great potential of EC and PC as THF substitutes, and provides experimental insights and practical guidance for optimizing Li-MEAS electrolytes in flow reactors.