Pathways of the Electrochemical Nitrogen Reduction Reaction: From Ammonia Synthesis to Metal-N₂ Batteries

Ammonia is considered as an alternative fuel resource for a sustainable green future. The production of ammonia involves the electrochemical nitrogen reduction reaction (NRR), which has gained considerable attention due to its eco-friendly resources and nonharmful byproducts. Even with the manifold works on NRR, the technique has not reached the industrial scale because of the impediments of NRR electrocatalysts, and in addition, state-of-the-art electrocatalysts have not yet been discovered. In this review, first, the mechanism of the NRR, key metrics, and operational procedures for NRR electrochemistry are presented. Then, the electrocatalyst designs for efficient NRR are briefly introduced, followed by a discussion on the influence of the electrolytes that enhance NRR performance. The counterion effects of electrolytes on NRR performance and strategies for suppressing the HER by electrolyte additives are also discussed. Later, the NRR mechanisms are upgraded, and a comprehensive review of metal-N₂ batteries is provided. This review summarizes the effective methods for performing the NRR and strategies to suppress the HER on various electrocatalysts by tuning electrolytes and their additives. The review concludes by discussing the prospects of metal-N₂ batteries. Graphical Abstract: [Figure not available: see fulltext.]