Ultralow overpotential nitrate reduction to ammonia via a three step relay mechanism

Ammonia plays a significant role in agriculture and the next-generation carbon-free energy supply. Electrocatalytic nitrate reduction to NH₃is attractive for nitrate removal and NH₃production under ambient conditions. However, the energy efficiency is limited by the high reaction overpotential. Here, we propose a three-step relay mechanism composed of a spontaneous redox reaction, electrochemical reduction, and electrocatalytic reduction to overcome this issue. Ru_xCo_yalloys are designed and adopted as model catalysts. Ru₁₅Co₈₅exhibits an onset potential of +0.4 V versus a reversible hydrogen electrode and an energy efficiency of 41.54 ± 1.72 %, which are both the best records. The high performance results in a low production cost of $0.49 ± 0.02 /kg_ammonia($0.58~1.02/kg_ammoniasold in the USA). Electrochemicalin situspectroscopy and theoretical simulations indicate that the three-step relay mechanism leads to excellent catalytic performance on Ru₁₅Co₈₅and can be extended to Ru_xFe_yand Ru_xNi_yalloys.