Self-Sustaining Dynamic Alkaline Microenvironment-Mediated Efficient Nitrate Electroreduction to Ammonia on MnFeOx in Neutral Electrolyte

Abstract

Electrocatalytic nitrate reduction (NO₃RR) that utilizing renewable electricity to convert nitrate pollutants in wastewater, represents a promising route for sustainable ammonia synthesis, yet its efficiency in neutral media is severely limited by sluggish kinetics and intense competition from hydrogen evolution reaction (HER). Herein, we introduce a “self-sustaining alkaline local microenvironment” strategy enabled by a MnFe dual-site oxide that concurrently serves as a structural scaffold and catalytic mediator, in which inactive Fe_Oh sites in FeO_x are selectively substituted by Mn while active Fe_Td sites are retained. Fe sites in 1D MnFeO_x activate NO₃⁻ and dynamically capture OH⁻ to form FeOOH, establishing a localized alkaline microenvironment around the active sites at electrode—electrolyte interface that effectively suppresses HER. Concurrently, Mn sites stabilize the high-valent Fe species and continuously split interfacial H₂O into OH⁻ and H*, ensuring the robust persistence of the alkaline microenvironment. The resulting 1D MnFeO_x catalyst delivers an NH₃ Faradaic efficiency of 95.9% (12.3 mg h⁻¹ cm⁻²) in neutral media and operates stably for over 20 h without degradation. By advancing local pH regulation from external intervention to intelligent self-regulation, this work offers a new insight in adaptive electrocatalyst design and regulating the interfacial microenvironment beyond NO₃RR.