Stabilizing Monoclinic CuWO ₄ by Zn Substitution and Oxygen Vacancies for Boosted Nitrate Reduction to Ammonia

Electrocatalytic nitrate reduction to ammonia (NO 3 RR) offers a promising route to couple nitrate remediation with sustainable NH 3 production, but practical implementation remains limited by sluggish charge transfer, parasitic hydrogen evolution, and insufficient catalyst durability. Here, we report a phase/defect codesign strategy in which Zn substitution stabilizes the monoclinic CuWO 4 framework while simultaneously enriching oxygen vacancies, creating a vacancy-rich and structurally robust heterometal oxide catalyst for efficient NO 3 RR. This dual-control approach differs fundamentally from doping-only or defect-only strategies because it not only tunes the local electronic structure and intermediate binding, but also preserves the catalytically favorable framework under prolonged electrolysis. The optimized Zn 1.0 -CuWO 4 -140 delivers an NH 3 yield of 51.8 mg h –1 mg cat –1 with a Faradaic efficiency (FE) of 84.2% at −1.3 V vs RHE in 0.1 M KOH and 0.1 M KNO 3, and retains stable performance for 60 h while maintaining the monoclinic phase. Large-area testing in a 5 × 5 cm 2 flow cell further verifies robust operation under continuous-flow conditions. DFT calculations reveal that Zn substitution lowers the energetic demand for key hydrogenation steps and kinetically favors *H addition over pathways leading to *N/N 2 formation. Beyond CuWO 4, this work highlights phase/defect codesign as a general strategy for heterometal oxides in NO 3 RR and other multistep electrocatalytic reactions, where activity, selectivity, and durability must be optimized simultaneously.