Selective NO_x^- Electroreduction to Ammonia on Isolated Ru Sites

Nitrate and nitrite (NO_x^-) are widespread contaminants in industrial wastewater and groundwater. Sustainable ammonia (NH₃) production via NO_x^- electroreduction provides a prospective alternative to the energy-intensive industrialized Haber-Bosch process. However, selectively regulating the reaction pathway, which involves complicated electron/proton transfer, toward NH₃ generation relies on the robust catalyst. A specific consideration in designing selective NO_x^--to-NH₃ catalysts should meet the criteria to suppress competing hydrogen evolution and avoid the presence of neighboring active sites that are in favor of adverse N-N coupling. Nevertheless, efforts in this regard are still inadequate. Herein, we demonstrate that isolated ruthenium sites can selectively reduce NO_x^- into NH₃, with maximal Faradaic efficiencies of 97.8% (NO₂^- reduction) and 72.8% (NO₃^- reduction) at -0.6 and -0.4 V, respectively. Density functional theory calculations simulated the reaction mechanisms and identified the *NO → *NOH as the potential rate-limiting step for NO_x^--to-NH₃ conversion on single-atom Ru sites.