Modulating *CO Adsorption Behavior: A Mechanistic Strategy for High-Efficiency C-N Coupling in Urea Electrochemical Synthesis.

Electrochemical urea synthesis through CO2 and nitrate/nitrite (NO3 -/NO2 -) co-reduction represents a revolutionary alternative pathway for urea formation. Although studies reveal that restraining C-intermediates desorption is beneficial for C-N coupling, *CO adsorption behaviors were usually described by *CO binding energy based on DFT calculations. The intrinsic reason why the *CO adsorption behaviors could modulate the activity for urea formation remains ambiguous. Herein, a series of high-density Cu1/M1-NOC electrocatalysts regarding single-atomically dispersed Cu1/Cu1, Cu1/Ni1, Cu1/Au1, or Cu1/Pd1 sites anchored on N, O-co-doped carbon were developed for electrochemical urea synthesis. In situ spectroscopy reveals that strengthening *CO binding energy not only enhances *CO coverage but also increases the proportion of linear *CO absorption configuration (*COL). The *COL with sp hybridization exhibits stronger electrophilicity than that for bridge adsorption, thereby favoring coupling with N-intermediates. Notably, a linear relationship was established by plotting urea yield versus *COL coverage. As such, the intrinsic reason for facilitating C─N coupling was originated from the local enrichment of *COL. The optimal Cu1/Pd1-NOC catalyst exhibits the high urea Faradaic efficiencies of 73.73% and 67.3% with NO2 - and NO3 - as N source, respectively. This research provides an effective strategy to boost urea performance by precisely controlling the *CO adsorption behaviors.