Amorphous Co₂O₃/Crystalline Cu Interface Enables Ultra-Rapid Nitrite Conversion for Integrated Cascade Electroreduction of Nitrate to Ammonia

Given serious nitrate (NO₃ ^-) pollution and the energy-intensive nature of traditional ammonia (NH₃) synthesis, the electrocatalytic NO₃ ^- reduction reaction (NO₃ ^-RR) offers a green route for NH₃ production. Copper (Cu)-based catalysts, although kinetically favorable for NO₃ ^--to-NO₂ ^- conversion, still suffer from sluggish *NO₂ reduction, resulting in poor NH₃ selectivity. Herein, a tandem catalysis strategy is adopted to fabricate a cobalt(III) oxide-Cu heterostructure on nickel foam (Co₂O₃-Cu/NF) to enhance NO₃ ^-RR activity. Coordination distortion and asymmetry confirm the distinctive amorphous nature of Co₂O₃. Results from online differential electrochemical mass spectrometry, electron paramagnetic resonance, and theoretical calculations indicate that Cu dominates the conversion of NO₃ ^- to NO₂ ^-, while Co sites work in tandem to optimize the NO₂ ^- adsorption, reduce the decisive transformation barrier from *NO₂ to *NO, and facilitate water dissociation (producing *H) for N-intermediate hydrogenation. Electrochemical kinetic tests confirm that Co₂O₃ incorporation promotes the conversion of NO₃ ^- to NO₂ ^- and enhances the deep hydrogenation capability for rapidly transforming NO₂ ^- into other intermediates. Co₂O₃-Cu/NF achieves a high NH₃ yield rate of 90.45 ± 0.76 mg h^-1 cm^-2 and NH₃ Faradaic efficiency (FE-NH₃) 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 NO₃ ^-RR technology.