Facile and Scalable Synthesis of Self-Supported Zn-Doped CuO Nanosheet Arrays for Efficient Nitrate Reduction to Ammonium

CuO has been regarded as a promising catalyst for the electrochemical reduction of nitrate (NO₃^-RR) to ammonium (NH₃); however, the intrinsic activity is greatly restricted by its poor electrical property. In this work, self-supported Zn-doped CuO nanosheet arrays (Zn-CuO NAs) are synthesized for NO₃^-RR, where the Zn dopant regulates the electronic structure of CuO to significantly accelerate the interfacial charge transfer and inner electron transport kinetics. The Zn-CuO NAs are constructed by a one-step etching of commercial brass (Cu₆₄Zn₃₆ alloy) in 0.1 M NaOH solution, which experiences a corrosion-oxidation-reconstruction process. Initially, the brass undergoes a dealloying procedure to produce nanosized Cu, which is immediately oxidized to the Cu₂O unit with a low valence state. Subsequently, Cu₂O is further oxidized to the CuO unit and reconstructed into nanosheets with the coprecipitation of Zn²⁺. For NO₃^-RR, Zn-CuO NAs show a high NH₃ production rate of 945.1 μg h^-1 cm^-2 and a Faradaic efficiency of up to 95.6% at −0.7 V in 0.1 M Na₂SO₄ electrolyte with 0.01 M NaNO₃, which outperforms the majority of the state-of-the-art catalysts. The present work offers a facile yet very efficient strategy for the scale-up synthesis of Zn-CuO NAs for high-performance NH₃ production from NO₃^-RR.