Multisite (Cu ⁰ /Cu ⁺ /Cu ²⁺ –Fe) Interfaces Enhance Nitrate Adsorption and Active Hydrogen Utilization for Ammonia Electrosynthesis from Neutral Nitrate

The electroreduction of hazardous nitrate (NO₃^-) to valuable ammonia (NH₃) represents a sustainable approach to environmental remediation and nitrogen recovery. However, most catalysts exhibit undesirable NH₃ yield rates and poor Faradaic efficiency (FE) for the NO₃^- reduction reaction (NO₃RR) in near-neutral and low-concentration NO₃^-environments. Herein, the Fe-doped multivalent copper oxide (Cu_<i>x</i>O-Fe) was prepared to construct multisite interfaces that promote NO₃^- adsorption and H₂O dissociation-protonation processes. The Cu_<i>x</i>O-Fe catalyst achieves a superior NH₃ yield rate of 3.5 mg·h^-1·mg_cat^-1 (3.9 mg·h^-1·cm^-2), an excellent FE of 97.7%, and a NH₃ selectivity of 98.7%, outperforming Fe oxide nanoparticle-decorated Cu_<i>x</i>O (Cu_<i>x</i>O-FeO_<i>y</i>NPs) (1.9 mg·h^-1·mg_cat^-1, 84.7%, and 98.2%) and most of the reported catalysts in the 50-200 ppm of NO₃^- electrolytes. The comprehensive <i>in situ</i> characterizations and theoretical calculations reveal that Fe doping modulates the electronic structure and charge distribution of multivalent Cu_<i>x</i>O, achieving a high-rate NH₃ synthesis by lowering *NO hydrogenation energy barriers and accelerating N-O bond cleavage. The NO₃RR (Cu sites of CuO-Fe) and H₂O dissociation (Fe sites of Cu-Fe) primarily occur at different active sites, favoring abundant NO₃^- activation and *H utilization noncompetitively. Especially, a high performance of the Cu_<i>x</i>O-Fe electrocatalyst in both actual surface water (NH₃ selectivity >94.3%) and complex landfill leachate (92.6% of maximum NH₃ selectivity) was achieved, demonstrating its promising practical application potential. This work paves an avenue for synthesizing high-activity and selective catalysts with multisite interfaces for advanced and scalable electrochemical applications.