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 mgcat–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.