Indirect electrosynthesis of ammonia from nitrogen and water by a magnesium chloride cycle at atmospheric pressure

Artificial N 2 fixation is one of the most important industrial processes for human beings. However, the current Haber-Bosch process based on fossil fuel suffers from unsustainability and a low N 2 to NH 3 conversion. Here, we report a magnesium chloride cycle for the synthesis of NH 3 from N 2 and H 2 O at atmospheric pressure. In this cycle, N 2 reacts with Mg to form Mg 3 N 2 . Mg and Cl 2 are produced by the electrolysis of molten MgCl 2 . NH 4 Cl is used to hydrogenolyze Mg 3 N 2 to produce NH 3 , with anhydrous MgCl 2 being regenerated. The cycle is closed via the reverse Deacon reaction to convert Cl 2 to HCl, which is captured as NH 4 Cl with the recyclable NH 3 . This indirect electrosynthesis produces NH 3 at an industry-acceptable rate with zero CO 2 emission, a coulombic efficiency >92%, and an energy consumption of ∼14.1 kWh/kg-NH 3 .