Self-supported iron-doped cobalt-copper oxide heterostructures for efficient electrocatalytic denitrification

The electrocatalytic reduction of nitrate ions (NO₃^-) to nitrogen gas (N₂) has emerged as an effective approach for mitigating nitrate pollution in water bodies. However, the development of efficient and highly selective cathode materials remains challenging. Conventional copper-based catalysts often exhibit low selectivity because they strongly adsorb oxygen. In this study, a straightforward solvothermal and pyrolysis method was used to grow iron-doped cobalt-copper oxide heterogeneous structures on copper foam surfaces (Fe-CoO/CuO@CF). Then, the effects of the applied potential, initial NO₃^- concentration, Cl^- concentration, electrolyte pH, and different catalysts on the catalyst performance were investigated. Compared with recently reported congeners, Fe-CoO/CuO@CF is less expensive and exhibits outstanding activity for NO₃^- reduction. Meanwhile, under a cathode potential of - 1.31 V vs. Ag/AgCl, Fe-CoO/CuO@CF degrades 98.6 % of NO₃^- in 200 min. In addition, when employing a method inspired by NH₄⁺ removal by breakpoint chlorination, N₂ selectivity over Fe-CoO/CuO@CF was raised from 10 % without Cl^- to 99.7 % when supplemented with Cl^-. The catalyst demonstrated excellent cyclic stability, maintaining a high electrocatalytic activity for the conversion of NO₃^- to N₂ gas over eleven cycles. Moreover, Fe-CoO/CuO@CF enabled 63.7 % removal of NO₃^- from wastewater (50 mg/L NO₃^--N) prepared from natural water, with 100 % conversion to N₂. Computational studies showed that iron doping decreased the free energy change of the intermediate of NO₃^- reduction reaction. This study provides an effective strategy for the electrochemical reduction of nitrate to nitrogen gas and offers good prospects for addressing nitrate pollution.