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

Graphical Lowering barriers : Bimetallic ZnCo 2 O 4 catalyst can promote nitrate electroreduction at room temperature. The electron-deficient Co active site can lower the energy barriers for the formation of *NO 2 intermediate and suppress the hydrogen evolution reaction, thus enhancing the selectivity and yield rate of electrochemical NO 3 − reduction to ammonia. Nitrate (NO 3 − ) 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 NO 3 − and produce ammonia (NH 3 ), known as a complement to the Haber–Bosch reaction. Currently, noble-metal electrocatalysts are often used in electrochemical reduction of NO 3 − , but high cost and scarcity limited their application. Herein, three-dimensional (3D) flower-like zinc cobaltite (ZnCo 2 O 4 ) electrocatalyst was developed to convert nitrate into ammonia at room temperature. The NH 3 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 Co 3 O 4 . In addition, the NH 3 faradaic efficiency of ZnCo 2 O 4 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 NO 3 − 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.