Co-Doped CuO Nanoarrays for Enhanced Electrocatalytic Nitrate Reduction to Ammonia via Active Hydrogen Regulation

Electrocatalytic reduction of nitrate (NO3–RR) has emerged as a promising technique for nitrate pollutant treatment, providing a viable pathway for nitrate removal and ammonia production. Copper oxide (CuO) electrocatalysts are particularly advantageous due to their low cost and favorable d-orbital energy alignment with the π-orbitals of nitrate molecules, which facilitates nitrate adsorption on the CuO surface and promotes the NO3–RR. However, CuO exhibits low selectivity for NH3 and is constrained by its low reduction rate at high potentials and competition with hydrogen evolution reactions at lower potentials, which hinders its practical application. To this end, cobalt-doped copper oxide nanoarrays (Co-doped CuO NAs) were hereby developed using a simple sequence of oxidation and hydrothermal methods. This nanostructure enhances the NO3–RR rate by providing additional active sites, thereby accelerating the reaction rate. Co doping effectively regulates the active hydrogen (H*) from water splitting, further enhancing the interaction with nitrate on the electrocatalyst surface and improving the NH3 yield. Specifically, in this work, Co-doped CuO NAs achieved a Faradaic efficiency of 95.99 ± 2.63% for ammonia production at −0.63 V vs RHE, with a rate of 8.41 ± 0.14 mg h–1 cm–2 and an ammonia selectivity of 98.30 ± 1.44%.