Electrochemical reduction conditioning modified Fe-based catalysts with structural disorders for efficient ammonium production from nitrite reduction

Abstract

Electrochemical reduction of NO2 -to NH4 + offers a direct, energy-efficient pathway for sustainable ammonia production by circumventing the rate-determining NO3 --to-NO2 -conversion that constrains traditional NO3 -reduction (NO3RR). Herein, we introduce an electrochemical reduction conditioning (ERC) strategy to control Fe2O3 at different reduction potentials, generating a series of catalysts with tunable Fe 3+ /Fe 2+ /Fe components and lattice strain. Comprehensive ex situ and in situ characterizations reveal that more negative ERC potentials induce greater structural disorder (i.e., tuned Fe/FeO/Fe2O3 components and pronounced lattice strain) which collectively enhance NO2 -adsorption, water dissociation and hydrogenation of intermediates while suppressing competing H2 evolution. Theoretical calculations support that these defective catalyst surface lower the energy barriers for NO2 -adsorption. As a result, the optimized ERC-treated Fe2O3 catalyst achieves a high NH4 + production rate of 153 nmol s -1 cm -2 , Faradaic efficiency of 93% and partial current density of ~ 96.5 mA cm -2 at -1.0 V vs RHE. Integration with plasma-generated NO2 --rich electrolytes further demonstrates stable, decentralized NH4 + production, yielding 32 nmol s -1 cm -2 . This work clarifies the mechanistic role of ERC-induced structural disorders in NO2RR and provides design principles for next-generation metal-oxide catalysts enabling sustainable nitrogencycle management.