Mechanistic insights into the stepwise lithium-mediated electrochemical nitrogen reduction for enhanced ammonia synthesis.

• A novel stepwise Li-mediated electrochemical nitrogen reduction (Li-NRR) was developed. • The decomposition of solid-electrolyte interphase was revealed by decoupling the continuous Li-NRR. • Zn exhibited fastest electron transfer and Li+ diffusion, demonstrating best Li-NRR performance. • The proportion of active lithium was demonstrated to influence the Faraday efficiency. • LiCl generated in protonation process was found to enhance the system stability and facilitate the recycling of lithium. The lithium-mediated electrochemical nitrogen reduction reaction (Li-NRR) is a sustainable route for green NH 3 synthesis. It accelerates the N 2 reduction by reacting the inert N ≡ N with active Li metal. However, the study on the mechanism of the Li-NRR process remains limited. Herein, a novel stepwise Li-NRR system is established to separately optimize the major steps of Li-NRR: lithium-ion reduction, lithium nitridation, and Li 3 N protonation. It is revealed that during the Solid Electrolyte Interface (SEI) decomposition, the carbon chains in organic species become shorter, and Li x BF y is converted to LiF, which is similar to the continuous Li-NRR. Contrary to the continuous Li-NRR, the O/C ratio decreases as the SEI decomposes due to the absence of ethanol. Commercial Cu, Ni, and Zn are employed as cathodes in the experiments at various currents. The highest Faraday efficiency of 33.2 % and ammonia yield rate of 1404.5 μg h−1 cm−2 are achieved on Zn electrode owing to its superior electron transfer and enhanced Li+ diffusion than those of Cu and Ni. The current has also been found to affect Faraday efficiency through the portion of active lithium in coulomb efficiency experiments. Moreover, the LiCl generated in protonation process is found to facilitate lithium cycling. [ABSTRACT FROM AUTHOR]