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.