Efficient electrocatalytic reduction of nitrate to ammonia at low concentration by copper-cobalt oxide nanowires with shell–core structure

Electrocatalytic nitrate reduction to ammonia (NO₃⁻RR) for removing nitrate from wastewater is a promising but challengeable technology that is increasingly studied. Herein, we developed an efficient CuO_x and CoCuO_x composed hybrid catalyst (CoCuO_x@CuO_x/copper foam (CF)), characteristic of distinctive shell–core nanowires grown on CF substrate with CuO_x core and CoCuO_x shell. The built-in electric field formed at the interface of the CoO/Cu₂O heterostructure promotes NO₃⁻ adsorption by modulating the charge distribution at the interface, which greatly improves the ammonia yield rate and Faradaic efficiency. At −0.2 V vs. reversible hydrogen electrode (RHE), CoCuO_x@CuO_x/CF achieves not only an excellent ammonia yield rate of up to 519.1 μg·h⁻¹·cm⁻² and Faradaic efficiency of 99.83% at 1 mM NO₃⁻ concentration, but also excellent mechanical stabilities. This study provides a novel pathway to design electrocatalyst for the removal of nitrate from dilute nitric acid solutions (≤ 2 mM).