Understanding Continuous Lithium-Mediated Electrochemical Nitrogen Reduction

Ammonia is a large-scale commodity chemical that is crucial for producing nitrogen-containing fertilizers. Electrochemical methods have been proposed as renewable and distributed alternatives to the incumbent Haber-Bosch process, which utilizes fossil fuels for ammonia production. Herein, we report a mechanistic study of lithium-mediated electrochemical nitrogen reduction to ammonia in a non-aqueous system. The rate laws of the main reactions in the system were determined. At high current densities, nitrogen transport limitations begin to affect the nitrogen reduction process. Based on these observations, we developed a coupled kinetic-transport model of the process, which we used to optimize operating conditions for ammonia production. The highest Faradaic efficiency observed was 18.5% ± 2.9%, while the highest production rate obtained was (7.9 ± 1.6) × 10−9 mol cm−2 s−1. Our understanding of the reaction network and the influence of transport provides foundational knowledge for future improvements in continuous lithium-mediated ammonia synthesis.