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

What the paper says

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 (CuxO-Fe) was prepared to construct multisite interfaces that promote NO3- adsorption and H2O dissociation-protonation processes. The CuxO-Fe catalyst achieves a superior NH3 yield rate of 3.5 mg·h-1·mgcat-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 CuxO (CuxO-FeOyNPs) (1.9 mg·h-1·mgcat-1, 84.7%, and 98.2%) and most of the reported catalysts in the 50-200 ppm of NO3- electrolytes. The comprehensive in situ characterizations and theoretical calculations reveal that Fe doping modulates the electronic structure and charge distribution of multivalent CuxO, 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 CuxO-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.