Mechanistic Insight into High Yield Electrochemical Nitrogen Reduction to Ammonia using Lithium Ions

Development of methods for economically feasible greener ammonia (NH₃) production is gaining tremendous scientific attention. NH₃ has its importance in fertilizer industry and it is envisaged as a safer liquid hydrogen carrier for futuristic energy resources. Here, an aqueous electrolysis based NH₃ production in ambient conditions is reported, which yields high faradaic efficiency (~12%) NH₃ via nitrogen reduction reaction (NRR) at lower over potentials (~ -0.6V vs. RHE or -1.1V vs. Ag/AgCl). Polycrystalline copper (Cu) and gold (Au) are used as electrodes for electrochemical NRR, where the electrolyte which yields high amount of NH₃ (~41 µmol/L) is 5M LiClO₄ in water with Cu as working electrode. A detailed study conducted here establishes the role of Li⁺ in stabilizing nitrogen near to the working electrode - augmenting the NRR in comparison to its competitor - hydrogen evolution reaction, and a mechanistic insight in to the phenomenon is provided. ¹⁵N₂ assisted labeling experiments are also conducted to confirm the formation of ammonia via NRR. This study opens up the possibilities of developing economically feasible electrodes for electrochemical NRR at lower energies with only transient modifications of electrodes during the electrolysis, unlike the studies reported on complex electrodes or electrolytes designed for NRR in aqueous medium to suppress the hydrogen generation.