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 g_NH3–N g_Cu^–1 h^–1, an NH₃–N selectivity of 90.1%, and a Faradaic efficiency of 91.3%, outperforming the Cu nanoparticles (1.8 g_NH3–N g_Cu^–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 mol_N^–1.