Electrochemical synthesis of ammonia is deemed as an alternative to the fossil-fuel-driven Haber-Bosch (HB) process, in which Li-mediated nitrogen reduction (LiNR) is the most promising scheme. Continuous lithium-mediated nitrogen reduction for ammonia synthesis (C-LiNR) has recently been reported in high-level journals with many foggy internal reactions. Synthesizing ammonia in a separate way may be profitable for understanding the mechanism of LiNR. Herein, an intermittent lithium-mediated nitrogen reduction for ammonia synthesis (I-LiNR) was proposed, three steps required for I-LiNR were achieved in the cathode chamber of a Li-N2 battery. Discharge, stand, and charge in the Li-N2 battery correspond to N2 lithification, protonation, and lithium regeneration, respectively. It can also realize the quasi-continuous process with practical significance because it could be carried out through identical batteries. Products such as Li3N, LiOH, and NH3 are detected experimentally, which demonstrate a definite reaction pathway. The mechanism of the Li-N2 battery, the Li-mediated synthesis of ammonia, and LiOH decomposition are explored through density functional theory calculations. The role of Li in dinitrogen activation is highlighted. It expands the range of LiOH-based Li-air batteries and may guide the study from Li-air to Li-N2; attention has been given to the reaction mechanism of Li-mediated nitrogen reduction. The challenges and opportunities of the procedure are discussed in the end.
Keywords: DFT calculations; Li−N2 battery; ammonia; metallic lithium; nitrogen reduction.