Electrochemical reduction of nitrate via Cu/Ni composite cathode paired with Ir-Ru/Ti anode: High efficiency and N2 selectivity

To address the severe nitrate contamination of water sources, a Cu/Ni bimetallic composite electrode was successfully prepared via cathodic electrodeposition method. Characterization by scanning electron microscopy, energy-dispersive spectroscopy, and X-ray diffraction confirmed that Cu nanoparticles were successfully deposited on the surface of Ni foam as irregular spherical structures with a diameters of 900 nm. The Cu/Ni electrode was applied as a cathode in nitrate electroreduction experiments, achieving nearly complete removal of nitrate within 60 min compared to a Ni foam electrode (15.0% removal). The improved performance was attributed to the dramatically increased catalytically active sites and the decreased resistance of the electrode, as shown by linear sweep voltammetry and electrochemical impedance spectroscopy analyses. The parameters influencing electrolysis, including current density, Cl− concentration, and solution pH were evaluated. It was concluded that (a) Increasing the current density favored nitrate removal, but reduced the electronic energy utilization efficiency; (b) Cl− presence hindered nitrate removal slightly, but facilitated NH4+-N removal significantly; (c) Acidic conditions were detrimental to nitrate and total nitrogen removal. Additionally, reusability experiments of the Cu/Ni electrode over eight cycles were performed. These indicated that the Cu/Ni electrode possessed excellent stability, maintaining a high removal efficiency of >95.0% over eight cycles. Finally, a possible removal pathway of nitrate electroreduction with the Cu/Ni cathode was proposed.