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

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