Single-Atom Copper-Bearing Cerium Oxide Electrocatalysts Embedded in an Integrated System Enable Sustainable Nitrogen Recycling from Natural Water Bodies

Electrocatalytic reduction of nitrate (NO3–) to ammonia (NH3) (NO3RR) coupled with NH3 separation represents a sustainable approach to mitigate nitrate pollution and recycle nitrogen from contaminated water. Nevertheless, this process is deemed impractical for contaminated natural water bodies owing to the limited presence of NO3––N (<50 mg L–1) and electrolytes and the relative abundance of scaling ions (Mg2+ and Ca2+). Furthermore, copper (Cu), as the primary NO3RR catalyst, generally suffers from NO2– accumulation and a prevalence of side hydrogen evolution. Herein, we develop an integrated system comprising sections of NO3– enrichment and NO3RR and NH3 collection, alongside a single-atom Cu-bearing CeO2 catalyst (Cu1/CeO2) for NO3RR. With this system, diluted NO3– is extracted from contaminated water using anion-exchange resins and then released into a concentrated NaCl aqueous solution, providing a solution with ample NO3––N (∼822 mg L–1) and electrolytes (∼1.7 M NaCl) while being free of scaling ions. Within this solution, the Cu1/CeO2 demonstrates an exceptional high and steady NH3–N production rate of 7.8 gNH3–N gCu–1 h–1, an NH3–N selectivity of 90.1%, and a Faradaic efficiency of 91.3%, outperforming the Cu nanoparticles (1.8 gNH3–N gCu–1 h–1, 46.3%, and 53.0%). In situ experiments and theoretical computations reveal a dual-site NO3RR mechanism involving the electron-deficient Cu1 site and adjacent oxygen vacancies, which collaborate to promote NO3– adsorption and lower conversion barrier while inhibiting hydrogen evolution. Finally, we implemented the integrated system along the Yangtze River, achieving nitrate elimination and nitrogen recycling with a competitive energy consumption of 1.36–1.54 kW h molN–1.