Rapid　industrial　growth　and　widespread　fertilizer　application　have　led　to　nitrate　contamination　in　water,　threatening　ecosystems　and　human　health.　There　is　growing　interest　in　developing　electrocatalysts　to　convert　nitrates　into　ammonia,　enabling　wastewater　recycling　and　transforming　harmful　substances　into　valuable　ammonia.　In　this　study,　we　presented　an　eco-friendly,　cost-effective　electrocatalyst　suitable　for　large-scale　industrial　production.　It　was　designed　specifically　for　the　electrochemical　reduction　of　NO3–　to　NH3　(NO3−RR).　Cu2O　nanoparticles　were　synthesized　on　Cu　foam　through　a　simple　one-step　in　situ　growth　approach.　The　conversion　of　Cu+,　serving　as　the　active　site　during　NO3−RR,　into　nanoscale　Cu　had　been　investigated.　Cu+sites　initiated　the　conversion　of　nitrate　to　nitrite　and　subsequently　facilitated　the　reduction　of　nitrite　to　ammonia　while　being　transformed　into　nano-grained　Cu.　The　newly　generated　Cu,　with　a　larger　specific　surface　area　and　lower　charge　transfer　resistance,　improved　Faradaic　efficiency　(FE)　for　NH3　in　the　NO3−RR　process.　As　a　result,　an　impressive　nitrate　removal　rate　of　100　%　and　a　relatively　high　ammonia　yield　rate　of　1514.67　µg　h−1　cm−2,　along　with　a　low　residue　of　nitrite-N　(0.21　ppm)　can　be　achieved　in　solutions　containing　100　ppm　of　nitrate-N.　©　2025