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

Electrocatalytic NO reduction (eNO3RR) is a sustainable method for purification of NO wastewater and NH recovery. Cu-based catalysts are promising for eNO3RR, but insufficient active hydrogen (*H) supply and *NO 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 NH synthesis from eNO3RR. It is efficient for NH synthesis with high Faradaic efficiencies of 88.7-99.7% and maximum NH yield of 6.20 mmol·h·cm at neutral solution, 10-140 mM NO and 50-1500 mA·cm. Experimental and theoretical results reveal that lattice oxygen regulates the electronic structure of OD-Cu NSs and promotes *NO conversion, while lattice strain enhances *H generation from water dissociation, resulting in the good performance for NH synthesis. The applicability of OD-Cu NSs is proved by the high recovery of ammonia compound from eNO3RR.