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Effective operation of electrocatalysts for the ammonia oxidation reaction (AOR) is typically constrained by poisoning, rapid corrosion, and low Faradaic efficiencies (FEs). Aiming to address these challenges, we present herein a robust silver oxide (AgOx) catalyst generated by in situ anodic electrodeposition from a solution of Tollen's reagent (Ag(NH3)2OH). When tested in 1 M KOH and 0.1 M NH3 at 1.1 V vs standard hydrogen electrode, AgOx catalyzes the AOR to nitrite at an FE of 70 ± 6% and a yield rate of 42 ± 7 nmol s–1 cm–2, on a time scale of 33 h, which is the highest performance reported so far. Our data suggest that the mechanism of the AgOx-catalyzed AOR is defined by pH, with the strongly alkaline conditions (>0.1 M KOH) favoring the heterogeneous electrocatalytic pathway producing nitrite. In turn, operation at <0.1 M KOH promotes the formation of N2 via a homogeneous reaction mediated by the Ag3+/2+ redox couple. Electrochemical and physical characterization, including by in situ X-ray absorption and Raman spectroscopy, suggests that the active sites within AgOx promoting nitrite production are Ag3+-based.
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