Promoting direct C─N coupling via NO intermediate modulation for highly selective electrochemical urea synthesis

The electrochemical synthesis of urea from carbon dioxide (CO₂) and nitrate (NO₃^-) is a sustainable route yet remains challenging, primarily due to slow carbon-nitrogen (C─N) coupling and competing ammonia (NH₃) formation. Here, we demonstrate highly selective synthesis by modulating nitric oxide (NO) intermediate behavior on molybdenum-manganese (Mo─Mn) diatomic sites. The high NO surface coverage and strong binding energy promote a NO dimerization pathway to form N─N, which subsequently allows for efficient carbon monoxide (CO) insertion to form urea. This mechanism achieves 93.3% N selectivity toward urea, with a high yield rate of 35.16 millimoles per hour per gram and a faradaic efficiency of 48.1% at -0.6 volts versus reversible hydrogen electrode, while effectively suppressing NH₃ by-product formation. Conversely, dual sites like copper-manganese (Cu─Mn) exhibit weak NO adsorption and low coverage, which suppress dimerization and favor the conventional pathway via NHCO intermediates, leading to predominant NH₃ formation (86.2% N selectivity). This work establishes a NO-mediated strategy for efficient urea synthesis with minimized competing reactions.