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

Electrocatalytic nitrate reduction reaction (NO 3 RR) is a promising alternative to the conventional Haber–Bosch NH 3 synthesis process. To address the incompatibility between high yield and high selectivity for NH 3 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 H 2 O without reducing NO 3 – active site utilization, providing sufficient protons for NO 3 – 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 NO 3 – adsorption, while Co sites favor H 2 O 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 NO 3 RR and promoting intermediate migration along the interface. These benefits give Co@CoO/NF the improved NH 3 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 NO 3 RR activity and selectivity, offering promising prospects for new energy applications.