Abstract: The development of a highly efficient and durable electrocatalyst for nitrate reduction reaction (NO₃RR) wastewater valorization to ammonia (NH₃) is a promising strategy. However, it is challenging to design scalable low-cost electrocatalysts with high activity, high selectivity, and long-term stability by a facile and simple method. Herein, we construct this scalable Cu-based nanoarray with muti-oxidation states grown directly on nickel foam (NF) substrate (Cu₂₊₁O@Cu/NF) using a facile molten salt method combined in-situ electrochemical reduction. The as-prepared Cu₂₊₁O@Cu/NF nanoarrays reveal a high NH₃ yield of 20.14 mg h^-1 cm^-2 at -0.95 V vs. a reversible hydrogen electrode (vs. RHE), Faradaic efficiency of 99.38% at -0.55 V vs. RHE in the neutral potassium phosphate (PBS) buffer solution with 50 mM NaNO₃, which is ascribed to its electron redistribution with abundant oxygen vacancies and favorable charge/mass transfer.

Key words: Cu-Cu₂₊₁O nanorods with multi-oxidation states, High NH₃ yield, Molten salt method, Neutral medium, Nitrate electrochemical reduction, Scalable fabrication