Debunking Pitfalls of Li-N<sub>2</sub> Cells for Ammonia Electroproduction: Is This Setup Affordable to Prove Nitro-Fixation before Lithium Plating?

Abstract

The Li-N₂ cell represents a fascinating device that opens a new pathway for ammonia electrosynthesis. It combines the unique property of lithium, which can spontaneously react with N₂ under mild conditions, with an energy-efficient solution to the challenging N₂ fixation reaction. However, such a battery-inspired setup may be susceptible to false-positive results and present some pitfalls. This work elucidates some critical aspects of Li-N₂ cells, aiming at identifying a reliable methodology to assess the electrochemical reduction of N₂ at the cathodic surface, avoiding misleading pathways. Despite the spontaneous nature of the reaction between lithium and N₂, it remains uncertain whether it is feasible to promote the electrochemical fixation of N₂ before reaching the lithium plating potential. This would involve lithium as an ion in the electrolyte, which should activate and enable N₂ reduction on the carbonaceous surface before any Li⁺ reduction occurs, i.e., at a potential higher than the lithium plating potential (-3.04 V vs SHE). This study discusses this possibility, searching for setup limitations, such as the presence of metallic lithium at the anode, and pitfalls, such as the use of cyclic voltammetry in different testing environments as a methodology to evaluate the formation of Li₃N before lithium plating occurs.