Electroreduction of nitrogen with almost 100% current-to-ammonia efficiency

Abstract

In addition to its use in the fertilizer and chemical industries¹, ammonia is currently seen as a potential replacement for carbon-based fuels and as a carrier for worldwide transportation of renewable energy². Implementation of this vision requires transformation of the existing fossil-fuel-based technology for NH₃ production³ to a simpler, scale-flexible technology, such as the electrochemical lithium-mediated nitrogen-reduction reaction^3,4. This provides a genuine pathway from N₂ to ammonia, but it is currently hampered by limited yield rates and low efficiencies^4-12. Here we investigate the role of the electrolyte in this reaction and present a high-efficiency, robust process that is enabled by compact ionic layering in the electrode-electrolyte interface region. The interface is generated by a high-concentration imide-based lithium-salt electrolyte, providing stabilized ammonia yield rates of 150 ± 20 nmol s^-1 cm^-2 and a current-to-ammonia efficiency that is close to 100%. The ionic assembly formed at the electrode surface suppresses the electrolyte decomposition and supports stable N₂ reduction. Our study highlights the interrelation between the performance of the lithium-mediated nitrogen-reduction reaction and the physicochemical properties of the electrode-electrolyte interface. We anticipate that these findings will guide the development of a robust, high-performance process for sustainable ammonia production.