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

In addition to its use in the fertilizer and chemical industries(1), ammonia is currently seen as a potential replacement for carbon-based fuels and as a carrier for worldwide transportation of renewable energy(2). Implementation of this vision requires transformation of the existing fossil-fuel-based technology for NH3 production(3) to a simpler, scale-flexible technology, such as the electrochemical lithium-mediated nitrogen-reduction reaction(3,4). This provides a genuine pathway from N-2 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 N-2 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.