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.