Insights into lattice oxygen and strains of oxide-derived copper for ammonia electrosynthesis from nitrate

Electrocatalytic NO3− reduction (eNO3RR) is a sustainable method for purification of NO3− wastewater and NH3 recovery. Cu-based catalysts are promising for eNO3RR, but insufficient active hydrogen (*H) supply and *NO2 poison of active sites have hindered their performance, and the catalytic mechanism remains ambiguous. Here, we report oxide-derived copper nanosheet arrays (OD-Cu NSs) with residual lattice oxygen and lattice strains to enhance NH3 synthesis from eNO3RR. It is efficient for NH3 synthesis with high Faradaic efficiencies of 88.7-99.7% and maximum NH3 yield of 6.20 mmol·h−1·cm−2 at neutral solution, 10-140 mM NO3− and 50-1500 mA·cm−2. Experimental and theoretical results reveal that lattice oxygen regulates the electronic structure of OD-Cu NSs and promotes *NO2 conversion, while lattice strain enhances *H generation from water dissociation, resulting in the good performance for NH3 synthesis. The applicability of OD-Cu NSs is proved by the high recovery of ammonia compound from eNO3RR. Electrocatalytic nitrate reduction is promising for NH3 synthesis, but it suffers from low NH3 efficiency. Here, the authors report oxide-derived copper with residual lattice oxygen and lattice strains to enhance NH3 synthesis via promoting active hydrogen supply and nitrite conversion.