Molecularly Engineered Ni–O–C Interfacial Sites on g-C3N4 for Efficient Electrocatalytic Urea Synthesis from CO2 and Nitrate

Nickel-based catalysts hold promise for urea electrosynthesis but often suffer from strong chemisorption of CO₂, poor stability, and uncontrolled structural evolution under reaction conditions. In this study, we report a molecularly engineered electrocatalyst, Ni-PDA@g-C₃N₄, that contains highly dispersed Ni–O–C interfacial sites for the efficient and selective synthesis of urea from CO₂ and nitrate under ambient conditions. The catalyst is synthesized by chelating Ni²⁺ ions with polydopamine (PDA) and anchoring them onto graphitic carbon nitride (g-C₃N₄), forming a robust hybrid interface. This architecture promotes the concurrent activation of CO₂ and NO₃^–, thereby facilitating C–N bond formation. The Ni-PDA@g-C₃N₄ catalyst achieved a urea yield of 1190.3 μg h^–1 mg_cat^–1 with a Faradaic efficiency of 18.03% and a nitrogen selectivity of 55.78% at −1.3 V vs RHE, along with excellent long-term stability. Density functional theory (DFT) calculations demonstrate that the Ni–O–C interface substantially reduces the energy barriers for key intermediates such as *NHO and *COOH, thus accelerating the C–N coupling process. This work highlights a molecular and interfacial design strategy that offers a promising route toward sustainable urea production from CO₂ and nitrogenous wastes.