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.