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 (NH 3 ) 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 NH 3 generation relies on the robust catalyst. A specific consideration in designing selective NO x - -to-NH 3 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 NH 3 , with maximal Faradaic efficiencies of 97.8% (NO 2 - reduction) and 72.8% (NO 3 - 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-NH 3 conversion on single-atom Ru sites.