Phosphorus-Tuned Cu/Cu2O@CoO-P Heterojunction on Copper Mesh for Promoting Neutral Electrochemical Nitrate Reduction from Water

Electrochemical nitrate reduction to ammonia (NO 3 RR) is a sustainable strategy that integrates environmental remediation with ammonia resource recovery. Current NO 3 RR studies mainly focus on high nitrate concentrations under idealized electrolyte conditions to achieve high ammonia yields. Under realistic water conditions, low NO 3 – concentrations, neutral media, and competing side reactions often result in sluggish kinetics, low removal efficiency, and undesirable nitrite accumulation. Herein, we report a facile strategy for constructing an interface-tunable Cu/Cu 2 O@CoO-P heterojunction through one-step regulation of the growth of CoO nanoneedles on copper mesh by tuning the phosphorus concentration. Phosphorus incorporation effectively modulates the electronic structure of the Co active sites and tunes the heterojunction interface, thereby optimizing the generation of adsorbed hydrogen (*H) and suppressing the hydrogen evolution reaction. This enables a well-matched two-step tandem pathway, where Cu/Cu 2 O facilitates the conversion of NO 3 – to NO 2 – , and the P-modulated CoO sites rapidly hydrogenate NO 2 – to NH 4 + , thus effectively preventing excessive NO 2 – accumulation. The optimized Cu/Cu 2 O@CoO-P achieves a high Faradaic efficiency (FE) of 97.11% for NH 4 + - N and an ammonia yield of 36.09 mg h –1 cm –2 at 10 mA cm –2 under neutral-pH conditions, along with excellent stability, retaining 98.45% of its performance after 20 cycles. Notably, the catalyst demonstrates exceptional practical applicability for ammonia recovery from real aquaculture tailwater in both batch mode and continuous-flow mode. This work offers new insights into the design of tunable heterojunction interfaces to achieve a well-matched and efficient tandem catalytic process, enabling effective remediation of low-concentration nitrate contamination and high ammonia recovery in real wastewater environments.