Atomically Dispersed Metal–Nitrogen–Carbon Catalysts for Electrochemical Nitrogen Transformations to Ammonia and Beyond

Abstract

The electrochemical reduction of reactive nitrogen species plays a critical role in achieving a pathway for the carbon-neutral synthesis of ammonia (NH3) and urea to produce synthetic fertilizers and as an energy storage vector. Atomically dispersed metal–nitrogen–carbon (M–N–C) catalysts have demonstrated great success in achieving efficient NH3 synthesis due to their full atom utilization, unique reaction pathways, high level of tailorability, and selectivity to mononitrogen products. This perspective focuses on M–N–C catalysts for electrochemical nitrogen transformations, where original experimental results utilizing 15 atomically dispersed mono- and bimetallic M–N–Cs are rigorously evaluated and compared with the literature for the highly controversial dinitrogen reduction reaction (N2RR). The current state for M–N–Cs applied for the reduction of nitrogen oxides (NO3–/NO2–), utilizing M–N–Cs both as the primary catalyst and as an active support, is discussed. Furthermore, the coreduction of NO3– and CO2 for C–N bond formation is presented with an emphasis on approaches for accurate urea detection to avoid false positives. Several possible C–N coupling pathways over metal-free nitrogen moieties, monometallic (M–Nx), and bimetallic active (M1–Nx + M2–Nx and M1–M2–Nx) sites are discussed. Finally, an outlook discussing the most significant challenges and opportunities in each of the three N-transformation pathways is discussed.