Coordinative Stabilization of Single Bismuth Sites in a Carbon-Nitrogen Matrix to Generate Atom-Efficient Catalysts for Electrochemical Nitrate Reduction to Ammonia.

Electrochemical nitrate reduction to ammonia powered by renewable electricity is not only a promising alternative to the established energy-intense and non-ecofriendly Haber-Bosch reaction for ammonia generation but also a future contributor to the ever-more important denitrification schemes. Nevertheless, this reaction is still impeded by the lack of understanding for the underlying reaction mechanism on the molecular scale which is necessary for the rational design of active, selective, and stable electrocatalysts. Herein, a novel single-site bismuth catalyst (Bi-N-C) for nitrate electroreduction is reported to produce ammonia with maximum Faradaic efficiency of 88.7% and at a high rate of 1.38 mg h -1 mg cat -1 at -0.35 V versus reversible hydrogen electrode (RHE). The active center (described as BiN 2 C 2 ) is uncovered by detailed structural analysis. Coupled density functional theory calculations are applied to analyze the reaction mechanism and potential rate-limiting steps for nitrate reduction based on the BiN 2 C 2 model. The findings highlight the importance of model catalysts to utilize the potential of nitrate reduction as a new-generation nitrogen-management technology based on the construction of efficient active sites.