Carbon-Confined Fe3C/Fe3N Janus Interfaces for Selective Nitric Oxide-to-Ammonia Electroreduction.

Electrocatalytic nitric oxide reduction to ammonia couples pollutant valorization with sustainable nitrogen conversion, but high activity and selectivity require concurrent control of NO transport, NO activation, and hydrogenation at the gas-liquid-solid interface. Here, we report a self-supported, noble-metal-free Fe3C/Fe3N@C catalyst, composed of earth-abundant Fe, C, and N, featuring defect-rich Fe3C/Fe3N Janus nanostructures confined within graphitic carbon. The catalyst achieves an NH3 yield rate of 468.3 µmol h-1 cm-2 with a Faradaic efficiency of 94.2% at -0.6 V versus RHE, placing it among the most efficient reported NORR electrocatalysts. Mechanistic studies reveal that the graphitic carbon shell facilitates NO diffusion by alleviating the steric and dynamic constraints imposed by the hydrogen-bonded water network. At the Janus interface, Fe3C sites preferentially adsorb and activate NO, whereas nitrogen-vacancy-rich Fe3N sites promote H2O dissociation to supply reactive *H for subsequent hydrogenation. This spatial coupling of mass-transfer promotion, NO activation, and interfacial *H generation enables efficient and selective NO-to-NH3 electroreduction. These findings establish carbon-confined, earth-abundant carbide/nitride Janus interfaces as a promising design principle for high-performance NORR catalysts.