Precise redox strategy to fabricate CuO/Cu2O hetero-electrodes for ultrafast electrochemical nitrate reduction into valuable ammonia resources

Electrochemical reduction of nitrate is a highly promising method for removing nitrate from water bodies. However, slow reaction rates have been a major challenge in its practical application. In this study, a novel CuO/Cu2O@CC hetero-electrode was developed by using a precise redox strategy, where CuO and Cu2O were simultaneously introduced to provide catalytic active sites for the reduction of nitrate into ammonia. This compositing design could significantly enlarge the electrochemically active surface area, reduce the electron transfer resistance and increase hydroxyl oxygen content on the electrode surface. The effect of operating parameters (cathodic potential, initial pH, supporting electrolyte concentration, initial NO3–−N concentration and coexisting Cl– concentration) on nitrate reduction was studied to optimize the reduction efficiency. Under −1.4 V (vs. Ag/AgCl) cathodic potentials and initial pH = 7 parameters, CuO/Cu2O@CC 3 achieved a remarkable 92.9% removal of 100 mg L–1 initial nitrate and a high ammonia selectivity of 78.33% in 1 h using 0.5 mol L–1 K2SO4 as supporting electrolyte, with a pseudo-first-order kinetic constant of 2.5856 h–1. Additionally, based on the experimental results, a reaction mechanism for the heterostructures electrode was proposed. The successful construction of CuO/Cu2O hetero-electrode provides a unique insight into the electrochemical reduction of nitrate.