关键词: 电化学, 固氮, 合成氨, Li-N₂电池, 金属锂

The production of ammonia using the Haber Bosch process cannot meet the goal of carbon neutral in the future, electrochemical nitrogen reduction reaction (NRR) to synthesize ammonia contains many advantages and is widely studied these years. Among them, the indirect lithium-mediated nitrogen reduction (LiNR) to synthesize ammonia, which has been successfully repeated, is considered to be a feasible way to produce ammonia via electrochemical method. Li-N₂ battery is another emerging direction, that reduce N₂ to Li₃N successfully during discharge, while received little attention. This paper, innovatively combining Li-N₂ battery system and LiNR, not only utilizes the discharge reduction reaction to fix N₂, but also co-reacts Li, N₂ and proton source (H₂O here) to produce NH₃. A common discharge and charge reaction are included, constituting a complete and clear lithium cycle procedure. During the discharge process, NH₃ generates continuously when N₂ and H₂O are fed together through the gas diffusion layer in the cathode, and the discharge potential in experiment is close to the theoretical value. When the constant current of 100 μA (0.05 mA•cm^-2) is used for 2 h discharge, the ammonia production is 0.67 μg•cm^-2 with Faraday efficiency of 3.2%. A contrast experiment shows that NH₃ generates only when N₂ and H₂O react together. Possible secondary reactions or reasons during discharging and mechanisms for ammonia production during charging are discussed. Lithium can be recycled between cathode and anode, based on Li-N₂ battery, by the recommended procedure, while NH₃ is produced every cycle and goes on. Cyclic ammonia production experiment demonstrates that the yield increases with the number of cycles almost linearly in 3 cycles. Finally, the discharge product LiOH is detected on the cathode inner surface, which proves that the discharge reaction proposed in this paper is valid. For the development of new types of nitrogen fixation methods, this scheme has great research and utilization spaces.

Key words: electrochemistry, nitrogen fixation, synthesis of ammonia, Li-N₂ battery, metallic lithium