Lithium-mediated electrochemical nitrogen reduction: Mechanistic insights to enhance performance

Summary: Green synthesis of ammonia by electrochemical nitrogen reduction reaction (NRR) shows great potential as an alternative to the Haber-Bosch process but is hampered by sluggish production rate and low Faradaic efficiency. Recently, lithium-mediated electrochemical NRR has received renewed attention due to its reproducibility. However, further improvement of the system is restricted by limited recognition of its mechanism. Herein, we demonstrate that lithium-mediated NRR began with electrochemical deposition of lithium, followed by two chemical processes of dinitrogen splitting and protonation to ammonia. Furthermore, we quantified the extent to which the freshly deposited active lithium lost its activity toward NRR due to a parasitic reaction between lithium and electrolyte. A high ammonia yield of 0.410 ± 0.038 μg s−1 cm−2 geo and Faradaic efficiency of 39.5 ± 1.7% were achieved at 20 mA cm−2 geo and 10 mA cm−2 geo, respectively, which can be attributed to fresher lithium obtained at high current density.