Magnesium-Mediated Electrochemical Synthesis of Ammonia

Metal-mediated electrochemical synthesis of ammonia (NH3) is a promising approach to activate N2 at room temperature. For instance, a lithium-mediated approach has been optimized to produce ammonia at high current density and selectivity. However, the scarcity of lithium and more negative plating potential pose limitations to scalability and energy efficiency. Alternative mediators have been proposed to address this challenge, but only calcium has shown some success, with NH3 Faradaic efficiency (FE) of ~50%, while voltage requirements far exceed 3 V. Here we report a Mg-mediated nitrogen reduction reaction (Mg-NRR), where N2 is activated on Mg to make nitride followed by its protolysis to make NH3 coupled with regeneration of Mg sites. Notably, we achieved an NH3 FE of 25.28 ± 3.80% at a current density of -45 mA/cm2, which amounts to NH3 current density of -11.30 ± 1.77 mA/cm2 under 6 bar conditions. Isotope labelled experiments were performed to confirm the source of ammonia and yielded similar performance with an FE of 25.15 ± 1.01%. NH3 production at the lowest total cell potential of 3V was demonstrated for the conversion of N2 to NH3. These promising results will motivate further research into these mediators and hold promise for enhancing the efficiency of electrochemical NH3 synthesis.