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

The electrocatalytic reduction of nitrate ions (NO ₃ ^- ) to nitrogen gas (N ₂ ) 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 NO ₃ ^- 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 NO ₃ ^- reduction. Meanwhile, under a cathode potential of - 1.31 V vs. Ag/AgCl, Fe-CoO/CuO@CF degrades 98.6 % of NO ₃ ^- in 200 min. In addition, when employing a method inspired by NH ₄ ⁺ removal by breakpoint chlorination, N ₂ 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 NO ₃ ^- to N ₂ gas over eleven cycles. Moreover, Fe-CoO/CuO@CF enabled 63.7 % removal of NO ₃ ^- from wastewater (50 mg/L NO ₃ ^- -N) prepared from natural water, with 100 % conversion to N ₂ . Computational studies showed that iron doping decreased the free energy change of the intermediate of NO ₃ ^- 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.
Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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