3D Flower‐Like Zinc Cobaltite for Electrocatalytic Reduction of Nitrate to Ammonia under Ambient Conditions

Nitrate (NO3- ) as a common pollutant of groundwater causes drinking water safety problems and seriously endangers people's health. Electrochemical reduction of nitrate to ammonia under ambient condition is a green and significant route to reduce the concentration of NO3- and produce ammonia (NH3 ), known as a complement to the Haber-Bosch reaction. Currently, noble-metal electrocatalysts are often used in electrochemical reduction of NO3- , but high cost and scarcity limited their application. Herein, three-dimensional (3D) flower-like zinc cobaltite (ZnCo2 O4 ) electrocatalyst was developed to convert nitrate into ammonia at room temperature. The NH3 yield rate could reach up to around 2100 μg mg-1 h-1 at a potential of -0.6 V vs. reversible hydrogen electrode (RHE), which was around 2.0 times higher than that of pristine Co3 O4 . In addition, the NH3 faradaic efficiency of ZnCo2 O4 electrocatalyst could reach around 95.4 % at potential of -0.4 V vs. RHE with good structural and morphological stability, which surpassed most reported non-noble metal-based electrocatalysts. Further studies concluded that the improved activity of electrocatalytic NO3- reduction was ascribed to the existence of abundant active sites and the charge transfer from Co atoms to Zn atoms after Zn doping. Importantly, this work opens a new path for the development of Co-based materials as electrocatalysts for reducing nitrate to ammonia.