Amorphous Co 2 O 3 /Crystalline Cu Interface Enables Ultra‐Rapid Nitrite Conversion for Integrated Cascade Electroreduction of Nitrate to Ammonia

ABSTRACT Given serious nitrate (NO 3 − ) pollution and the energy‐intensive nature of traditional ammonia (NH 3 ) synthesis, the electrocatalytic NO 3 − reduction reaction (NO 3 − RR) offers a green route for NH 3 production. Copper (Cu)‐based catalysts, although kinetically favorable for NO 3 − ‐to‐NO 2 − conversion, still suffer from sluggish *NO 2 reduction, resulting in poor NH 3 selectivity. Herein, a tandem catalysis strategy is adopted to fabricate a cobalt(III) oxide‐Cu heterostructure on nickel foam (Co 2 O 3 ‐Cu/NF) to enhance NO 3 − RR activity. Coordination distortion and asymmetry confirm the distinctive amorphous nature of Co 2 O 3 . Results from online differential electrochemical mass spectrometry, electron paramagnetic resonance, and theoretical calculations indicate that Cu dominates the conversion of NO 3 − to NO 2 − , while Co sites work in tandem to optimize the NO 2 − adsorption, reduce the decisive transformation barrier from *NO 2 to *NO, and facilitate water dissociation (producing *H) for N‐intermediate hydrogenation. Electrochemical kinetic tests confirm that Co 2 O 3 incorporation promotes the conversion of NO 3 − to NO 2 − and enhances the deep hydrogenation capability for rapidly transforming NO 2 − into other intermediates. Co 2 O 3 ‐Cu/NF achieves a high NH 3 yield rate of 90.45 ± 0.76 mg h −1 cm −2 and NH 3 Faradaic efficiency (FE‐NH 3 ) of 93.4% ± 2.5%. This work overcomes the inherent limitations of Cu‐based catalysts through crystalline‐amorphous dual‐site tandem synergy, offering new insights for developing NO 3 − RR technology.