In Situ Derivation\nof Dual-Active Co/CoO Heterojunction\nNanoarrays for Synergistic Catalytic NH<sub>3</sub> Synthesis

Electrocatalytic\nnitrate reduction reaction (NO<sub>3</sub>RR)\nis a promising alternative to the conventional Haber–Bosch\nNH<sub>3</sub> synthesis process. To address the incompatibility between\nhigh yield and high selectivity for NH<sub>3</sub> synthesis under\nalkaline conditions, we report an in situ-derived Co/CoO heterojunction\nnanoarray bifunctional catalyst (Co@CoO/NF). The dual-site catalytic\nconfiguration accelerates the H–OH bond cleavage of H<sub>2</sub>O without reducing NO<sub>3</sub><sup>–</sup> active site\nutilization, providing sufficient protons for NO<sub>3</sub><sup>–</sup> hydrogenation and suppressing competitive hydrogen evolution at\nhigh overpotentials. Density functional theory calculations together\nwith kinetic analysis reveal that electron migration between heterogeneous\ninterfaces enhances Co@CoO/NF’s targeted adsorption: CoO sites\nfavor NO<sub>3</sub><sup>–</sup> adsorption, while Co sites\nfavor H<sub>2</sub>O adsorption. The synergistic effect of defect\nsites from annealing and the in situ-derived nanoarray structure from\nmetal–organic frameworks improve electron transfer and mass\ntransport efficiency, lowering the activation energy barrier for NO<sub>3</sub>RR and promoting intermediate migration along the interface.\nThese benefits give Co@CoO/NF the improved NH<sub>3</sub> yield rate\nof 129.83 mg h<sup>–1</sup> cm<sup>–2</sup>, a Faradaic\nefficiency of 96.49%, and a current density of 1637.43 mA cm<sup>–2</sup>, along with long-term stability over a continuous 40 h cycle. This\nstudy presents a practical strategy for a dual active site catalyst\nelectrode with enhanced NO<sub>3</sub>RR activity and selectivity,\noffering promising prospects for new energy applications.