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

The electrocatalytic reduction of nitrate ions (NO) to nitrogen gas (N) 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 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 reduction. Meanwhile, under a cathode potential of - 1.31 V vs. Ag/AgCl, Fe-CoO/CuO@CF degrades 98.6 % of NO in 200 min. In addition, when employing a method inspired by NH removal by breakpoint chlorination, N 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 to N gas over eleven cycles. Moreover, Fe-CoO/CuO@CF enabled 63.7 % removal of NO from wastewater (50 mg/L NO-N) prepared from natural water, with 100 % conversion to N. Computational studies showed that iron doping decreased the free energy change of the intermediate of NO 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.