Magnesium-Mediated Electrochemical Synthesis of Ammonia

Metal-mediated electrochemical synthesis of ammonia (NH₃) is a promising method to activate N₂ at room temperature. While a Li-mediated approach has been optimized to produce NH₃ at high current density and selectivity, Li's scarcity and its highly negative plating potential limit scalability and energy efficiency. Alternative mediators have been proposed, but only Ca has shown some promise, achieving ≈50% Faradaic efficiency (FE), though requiring voltages beyond -3 V. Here, we report a Mg-mediated nitrogen reduction reaction (Mg-NRR), where N₂ is activated on Mg to form Mg₃N₂, followed by protolysis to release NH₃ and regenerate Mg. A notable NH₃ FE of 25.28 ± 3.80% is achieved at a current density of -45 mA cm^-2, corresponding to an NH₃ partial current density of -11.30 ± 1.77 mA cm^-2 under 6 bar N₂. Isotope-labeled experiments confirm that NH₃ originates from N₂, with similar FE (25.15 ± 1.01%). Importantly, NH₃ production is demonstrated at a total cell potential as low as -3 V. This Li-free Mg-NRR system offers key advantages, including lower energy input and use of earth-abundant materials, making it a scalable route for sustainable NH₃ synthesis.