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

Abstract

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.