ZnO Nanowire Arrays Decorated with Cu Nanoparticles for High-Efficiency Nitrate to Ammonia Conversion

The electrocatalytic transformation of waste nitrate into useful ammonia is a “one stone, two birds” strategy, which is commendatory from the viewpoint of the environment. In this vein, developing catalysts with high efficiency, selectivity, and stability is desired to make the attractive technology viable. Herein, we synthesized an economical and scalable electrocatalyst of Cu nanoparticles dispersed onto ZnO nanowire arrays (Cu@ZnO NWA) for nitrate reduction reaction (NO₃^-RR). This catalyst constructed on the Cu foam achieved a high ammonia yield of ∼6.03 mg cm^-2 h^-1, a Faradaic efficiency of ∼89.14%, and good stability for the NO₃^-RR in the Ar-saturated 0.1 M KOH electrolyte with the presence of 0.05 M KNO₃, superior to most Cu-based catalysts reported in the literature. According to electrochemical measurements and density functional theory calculations, ZnO nanowires offer stable support to accomplish uniform dispersion of Cu nanoparticles and provide a synergy to boost electrocatalytic properties of Cu catalysts. This synergistic effect may originate from the electronic localization at the interface of Cu nanoparticles and ZnO nanowires, resulting in the electron deficiency of the Cu@ZnO NWA surface. Therefore, the promotional mechanisms are associated with enhanced adsorption of the electronegative nitrate ions and boosted charge transfer during the NO₃^-RR process. Notably, the Cu@ZnO NWA catalyst can be synthesized on most conductor surfaces through a flexible combination of electrodeposition and hydrothermal techniques, showing good commonality and scalability, thus having a vast industrialization potential for practical application.