Engineering the Electronic Localization of Metastable Fe²⁺-O-Co³⁺ Bimetallic Sites for Superior Electrochemical Ammonia Production

Electrocatalytic nitrate reduction represents a green route for ammonia (NH₃) generation. Nevertheless, the mismatched kinetics between active hydrogen supply and nitrogen oxide reduction processes give rise to the accumulation of nitrite or competitive hydrogen evolution reactions, thereby resulting in suboptimal NH₃ selectivity and Faradic efficiency. Herein, the reconstruction of partial Co and Fe sites in layered double hydroxides (LDHs) is successfully induced, transforming their coordination environments from octahedral to tetrahedral configurations. The structural evolution in the catalyst (denoted as CoFe LDH-Ar₂₀) leads to the formation of metastable Fe²⁺_Td-O-Co³⁺_Oh bimetallic sites with unsaturated metal coordination. These metastable dual sites feature concurrent Co and Fe atoms with enhanced electron localization. Consequently, Co sites lower the energy barrier for the *NO → *NOH step, while Fe sites promote active hydrogen generation, ultimately boosting NH₃ production over CoFe LDH-Ar₂₀. This catalyst achieves an NH₃ yield rate of 2.28 mmol cm⁻² h⁻¹ with a Faradic efficiency of 96.64% at −0.40 V versus reversible hydrogen electrode and maintains stability over 100 h in a flow cell. It also combines spark discharge non-thermal plasma with CoFe LDH-Ar₂₀ catalyzed electroreduction of NO_x⁻ to NH₃, achieving high-efficiency tandem synthesis of NH₃ from air.