Electrocatalytic Nitrate Reduction on Oxide-Derived Silver with Tunable Selectivity to Nitrite and Ammonia

Removing excess nitrate (NO3-) from waste streams has become a significant environmental and health topic. However, realizing highly selective NO3- conversion toward N-2, primarily via electrocatalytic conversions, has proven challenging, largely because of the kinetically uncontrollable NO3--to-NO2- pathway and unfavorable N-N coupling. Herein, we discovered unique and ultra-high electrocatalytic NO3--to-NO(2)(-)activity on oxide-derived silver (OD-Ag). Up to 98% selectivity and 95% Faradaic efficiency (FE) of NO2- were observed and maintained under a wide potential window. Benefiting from the superior NO3--to-NO(2)(-)activity, further reduction of accumulated NO2- to NH4+ was well regulated by the cathodic potential and achieved an NH4+ FE of 89%, indicating a tunable selectivity to the key nitrate reduction products (NO2- or NH4+) on OD-Ag. Density functional theory computations provided insights into the unique NO2- selectivity on Ag electrodes compared with Cu, showing the critical role of a proton-assisted mechanism. Based on the ultra-high NO3--to-NO2- activity on OD-Ag, we designed a novel electrocatalytic-catalytic combined process for denitrifying real-world NO3--containing agricultural wastewater, leading to 95+% of NO3- conversion to N-2 with minimal NOX gases. In addition to the wastewater treatment process to N-2 and the electrochemical synthesis of NH3, NO2- derived from electrocatalytic NO3- conversion can serve as a reactive platform for the distributed production of various nitrogen products.