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 (NH 3 ) via electrochemical nitrate reduction reactions (NITRRs). Low-cost, scalable, and efficient cathodic materials need to be developed to enhance the NH 3 production rate. Here, in situ electrodeposition was adopted to fabricate a foamy Cu-based heterojunction electrode containing both Cu-defects and oxygen vacancy loaded Cu 2 O (OVs-Cu 2 O), which achieved an NH 3 yield rate of 3.59 mmol h –1 cm –2, NH 3 Faradaic efficiency of 99.5%, and NH 3 selectivity of 100%. Characterizations and theoretical calculations unveiled that the Cu-defects and OVs-Cu 2 O 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 NO 3 -to-NO 2 and NO 2 -to-NH 3 . An integrated system was further built to combine wet flue gas denitrification and desulfurization, simultaneously converting NO and SO 2 to produce the (NH 4 ) 2 SO 4 fertilizer. This study offers new insights into the application of low-cost Cu-based cathode for electrochemically driven wet denitrification wastewater valorization.