LAUSR

Electrocatalytic ammonia (NH3) synthesis from the reduction of nitrate (NO3-) is one of the effective and mild methods to treat nitrogen-containing wastewater from stationary sources and to obtain NH3 readily compared with the Haber-Bosch process. However, the low efficiency of electrocatalytic NO3- reduction to NH3 on traditional Cu-based catalysts hinders their practical application. Here, we prepare a Au/Cu single atom (SA) alloy (Au/Cu SAA) that shows a high performance of NH3 synthesis with 99.69% Faradaic efficiency at -0.80 V vs RHE. The structures of Au SAs and alloyed Au/Cu are confirmed by the detailed characterizations. Online differential electrochemical mass spectrometry confirms the occurrence of key reaction intermediates (*NO2, *NO, and *NH3). Density functional theory calculations demonstrate that Au SAs efficiently reduce the adsorption energy of *NO3-, and the newly formed Au-Cu bonds boost the reduction process of *NO2 to *NO. Meanwhile, Au/Cu SAAs produce significantly less N2 and N2O byproducts due to the prohibition of N-N coupling on single atoms, which finally leads to excellent Faradaic efficiency and NH3 selectivity.