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 (NOx) 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.