In Situ Derivation of Dual-Active Co/CoO Heterojunction Nanoarrays for Synergistic Catalytic NH3 Synthesis

Electrocatalytic nitrate reduction reaction (NO₃RR) is a promising alternative to the conventional Haber–Bosch NH₃ synthesis process. To address the incompatibility between high yield and high selectivity for NH₃ synthesis under alkaline conditions, we report an in situ-derived Co/CoO heterojunction nanoarray bifunctional catalyst (Co@CoO/NF). The dual-site catalytic configuration accelerates the H–OH bond cleavage of H₂O without reducing NO₃^– active site utilization, providing sufficient protons for NO₃^– hydrogenation and suppressing competitive hydrogen evolution at high overpotentials. Density functional theory calculations together with kinetic analysis reveal that electron migration between heterogeneous interfaces enhances Co@CoO/NF’s targeted adsorption: CoO sites favor NO₃^– adsorption, while Co sites favor H₂O adsorption. The synergistic effect of defect sites from annealing and the in situ-derived nanoarray structure from metal–organic frameworks improve electron transfer and mass transport efficiency, lowering the activation energy barrier for NO₃RR and promoting intermediate migration along the interface. These benefits give Co@CoO/NF the improved NH₃ yield rate of 129.83 mg h^–1 cm^–2, a Faradaic efficiency of 96.49%, and a current density of 1637.43 mA cm^–2, along with long-term stability over a continuous 40 h cycle. This study presents a practical strategy for a dual active site catalyst electrode with enhanced NO₃RR activity and selectivity, offering promising prospects for new energy applications.