Magnesium-Mediated Electrochemical Synthesis of Ammonia.

Metal-mediated electrochemical synthesis of ammonia (NH) is a promising method to activate N at room temperature. While a Li-mediated approach has been optimized to produce NH 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 N is activated on Mg to form MgN, followed by protolysis to release NH and regenerate Mg. A notable NH FE of 25.28 ± 3.80% is achieved at a current density of -45 mA cm, corresponding to an NH partial current density of -11.30 ± 1.77 mA cm under 6 bar N. Isotope-labeled experiments confirm that NH originates from N, with similar FE (25.15 ± 1.01%). Importantly, NH 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 NH synthesis.