Enhanced Nitric Oxide Electroreduction to Ammonia via Modulating Spin‐Polarization of Fe Single‐Atom Catalysts

Abstract Electrochemical nitric oxide reduction (NORR) offers a sustainable pathway to ammonia (NH ₃ ) while removing toxic NO from industrial emissions. However, high efficiency is hindered by the difficulty of synchronizing multi‐proton/electron transfers to accelerate NO hydrogenation and suppress competing hydrogen evolution. Here, an Fe single‐atom catalyst (FeSAC) is reported that achieves record NORR activity through spin‐state engineering. Using a top‐down electrospinning approach, self‐supported S,N‐doped carbon fiber films hosting Fe‐N ₃ S ₁ sites are fabricated. This catalyst delivers an NH ₃ yield rate of 140.58 µmol h ⁻¹ cm ⁻² with a Faradaic efficiency of 96.28%, outperforming nearly all reported SACs. Mechanistic analysis reveals that sulfur doping induces a high‐spin Fe ³⁺ → low‐spin Fe ²⁺ transition, suppressing spin polarization, strengthening NO adsorption, and facilitating proton supply to accelerate hydrogenation. These results establish spin‐state modulation as a powerful paradigm for designing next‐generation single‐atom catalysts for complex multi‐proton/electron electrocatalytic transformations, such as the electrosynthesis of ammonia.