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 (NO 3 – ) to valuable ammonia (NH 3 ) represents a sustainable approach to environmental remediation and nitrogen recovery. However, most catalysts exhibit undesirable NH 3 yield rates and poor Faradaic efficiency (FE) for the NO 3 – reduction reaction (NO 3 RR) in near-neutral and low-concentration NO 3 – environments. Herein, the Fe-doped multivalent copper oxide (Cu x O–Fe) was prepared to construct multisite interfaces that promote NO 3 – adsorption and H 2 O dissociation-protonation processes. The Cu x O–Fe catalyst achieves a superior NH 3 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 NH 3 selectivity of 98.7%, outperforming Fe oxide nanoparticle-decorated Cu x O (Cu x O–FeO y 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 NO 3 – electrolytes. The comprehensive in situ characterizations and theoretical calculations reveal that Fe doping modulates the electronic structure and charge distribution of multivalent Cu x O, achieving a high-rate NH 3 synthesis by lowering *NO hydrogenation energy barriers and accelerating N–O bond cleavage. The NO 3 RR (Cu sites of CuO–Fe) and H 2 O dissociation (Fe sites of Cu–Fe) primarily occur at different active sites, favoring abundant NO 3 – activation and *H utilization noncompetitively. Especially, a high performance of the Cu x O–Fe electrocatalyst in both actual surface water (NH 3 selectivity >94.3%) and complex landfill leachate (92.6% of maximum NH 3 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.