Lattice‐Confined Ru Creates Electron‐Deficient Fe(II)─Ov─Ru Atomic Interface for Efficient Nitrate‐to‐Ammonia Electrosynthesis

ABSTRACT Electrocatalytic nitrate reduction reaction (NITRR) is promising but severely limited by sluggish reaction kinetics and inefficient proton coupling. Herein, we report a lattice‐confinement strategy triggering ruthenium doping embedded in Fe 3 O 4 nanocrystals anchored on porous N‐doped carbon nanofibers, creating self‐adaptive electron‐deficient Fe(II)‐oxygen vacancy‐Ru (Fe(II)‐Ov‐Ru) atomic interfaces, which simultaneously enhances water dissociation for active hydrogen ( * H) supply. This atomic‐scale division of labor enables efficient nitrate adsorption and activation at Fe(II)‐Ov sites, coupled with accelerated proton delivery from neighboring Ru centers, thereby overcoming kinetic bottlenecks and suppressing nitrite accumulation and hydrogen evolution. As a result, the optimized catalyst achieves an outstanding ammonia yield of 49.2 mg h − 1 mg cat − 1 and a Faradaic efficiency of 92.8% at −1.4 V vs. RHE in neutral electrolyte, with excellent cycling stability (>20 cycles) and high selectivity (FE > 80%) across a wide pH range (1–14), outperforming most state‐of‐the‐art NITRR catalysts. Operando spectroscopy, * H monitoring, and density functional theory calculations identify * NO 2 reduction as the rate‐determining step and reveal its substantial energy barrier lowering via Ru‐induced electronic modulation. Furthermore, the catalyst delivers stable operation for over 50 h at an industrial‐grade current density of 400 mA cm − 2 in a flow‐cell electrolyzer. By integrating urea oxidation at the anode and recovering ammonia as high‐purity struvite fertilizer, this work establishes a scalable and energy‐efficient platform for sustainable nitrate valorization.