Electrochemical Reduction of Flue Gas Denitrification Wastewater to Ammonia Using a Dual-Defective Cu₂O@Cu Heterojunction Electrode

Wet flue gas denitrification offers a new route to convert industrial nitrogen oxides (NO_x) into highly concentrated nitrate wastewater, from which the nitrogen resource can be recovered to ammonia (NH₃) via electrochemical nitrate reduction reactions (NITRRs). Low-cost, scalable, and efficient cathodic materials need to be developed to enhance the NH₃ production rate. Here, in situ electrodeposition was adopted to fabricate a foamy Cu-based heterojunction electrode containing both Cu-defects and oxygen vacancy loaded Cu₂O (OVs-Cu₂O), which achieved an NH₃ yield rate of 3.59 mmol h^–1 cm^–2, NH₃ Faradaic efficiency of 99.5%, and NH₃ selectivity of 100%. Characterizations and theoretical calculations unveiled that the Cu-defects and OVs-Cu₂O heterojunction boosted the H* yield, suppressed the hydrogen evolution reaction (HER), and served as dual reaction sites to coherently match the tandem reactions kinetics of NO₃-to-NO₂ and NO₂-to-NH₃. An integrated system was further built to combine wet flue gas denitrification and desulfurization, simultaneously converting NO and SO₂ to produce the (NH₄)₂SO₄ fertilizer. This study offers new insights into the application of low-cost Cu-based cathode for electrochemically driven wet denitrification wastewater valorization.