Regulating Defect‐Coordinated Single‐Iron‐Atom Catalysts for Efficient Nitrate Reduction Reactions

ABSTRACT Electrocatalytic nitrate reduction represents a sustainable strategy to mitigate nitrogen cycle imbalance by converting NO 3 − into NH 3 under ambient conditions. However, conventional catalysts usually suffer from limitations in activity–selectivity–stability synergy. Herein, we propose a rational design guided by density functional theory calculation to engineer defect‐coordinated iron single‐atom catalysts (Fe─N 2 , Fe─N 3 , and Fe─N 4 ) for efficient electrocatalytic nitrate reduction. The superior Fe─N 2 catalyst with asymmetric coordination geometry achieves an unprecedented nitrate‐to‐ammonia conversion efficiency of 29,700 mg N/g at −0.65 V (vs. reversible hydrogen electrode) with 100% NH 3 selectivity as well as exceptional durability, maintaining > 95% activity over 480 h of continuous operation. In situ X‐ray absorption near‐edge structure directly captures dynamic valence‐state modulation of Fe sites under reaction conditions, coupled with stable Fe–N coordination, confirming electron‐density enrichment at active sites and robust structural integrity. Online differential electrochemical mass spectrometry and in situ Raman spectroscopy reveal the sequential reduction pathway (NO 3 − → NO 2 − → NO → NH 2 OH → NH 3 ), directly correlating the asymmetric Fe─N 2 coordination with optimized reaction kinetics. Practical validation in a continuous‐flow reactor demonstrates > 98% nitrogen removal efficiency for 1.0 L nitrate‐contaminated wastewater (100 ppm NO 3 − –N) within four cycles through using this Fe─N 2 ‐based electrode, achieving World Health Organization (WHO)‐compliant drinking water standards. This work establishes asymmetric Fe─N 2 coordination as a paradigm for high‐performance nitrate reduction, bridging computational design with scalable synthesis to advance sustainable nitrogen valorization and environmental remediation.