Electrocatalytic Reactive Capture of NO from O2-Containing Simulated Flue Gas Using Highly O2-Resistant Fe2+-(salen-SO3) for NH3 Synthesis

Abstract

Efficient removal of nitric oxide (NO) from flue gases remains a significant environmental challenge due to its low concentration, poor water solubility, and the presence of oxygen, which deactivates traditional NO absorbents such as Fe²⁺-EDTA. Herein, we present an electrochemistry-based reactive NO capture system using SO₃-functionalized Fe²⁺-salen as an NO absorbent with outstanding oxygen resistance. The unique tetracoordinate structure of the salen-SO₃ ligand reduces the electron density at the Fe²⁺ center, preventing its oxidation to Fe³⁺ under air exposure. Coupled with highly porous NiMo electrocatalysts, the system achieves an NH₃ production rate of 2.0 mmol h^–1 cm^–2_geo with 97% Faraday efficiency under 100% NO. This continuous NO capture and conversion into NH₃ was maintained under air-exposed conditions at 60% of the performance level under 100% NO, with stability over 160 h. Mechanistic studies reveal that Fe²⁺ is the critical active site for NO reduction and elucidate complete reaction pathways for NH₃ synthesis.