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 NO₃⁻ into NH₃ 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─N₂, Fe─N₃, and Fe─N₄) for efficient electrocatalytic nitrate reduction. The superior Fe─N₂ 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% NH₃ 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 (NO₃⁻ → NO₂⁻ → NO → NH₂OH → NH₃), directly correlating the asymmetric Fe─N₂ 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 NO₃⁻–N) within four cycles through using this Fe─N₂-based electrode, achieving World Health Organization (WHO)-compliant drinking water standards. This work establishes asymmetric Fe─N₂ coordination as a paradigm for high-performance nitrate reduction, bridging computational design with scalable synthesis to advance sustainable nitrogen valorization and environmental remediation.

Keywords

ammonia selectivity / density functional theory / electrocatalytic nitrate reduction / single-atom catalysts

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2026 The Author(s). Carbon Energy published by Wenzhou University and John Wiley & Sons Australia, Ltd.