Directing the C–N Coupling Pathway Enables Efficient Urea Electrosynthesis

Electrocatalytic synthesis of urea presents a promising approach to closing the artificial nitrogen cycle. However, a major challenge arises from the sluggish C-N coupling step in urea formation compared to other competing electrochemical steps involving nitrate and CO2 reduction, ultimately limiting the urea selectivity and energy efficiency during the coelectroreduction of nitrate and CO2. In this study, we identify *NO2 as a key intermediate that governs urea activity and selectivity as it can either undergo hydrogenation or couple with CO2 to form the desired C-N bond. Our theoretical investigations reveal that a decrease in the adsorption energy of *NO2 on Cu can suppress *NO2 hydrogenation while enhancing its coupling with CO2 to favor C-N bond formation. We further discover that doping of Cu with boron increases the energy requirement for *NO2 hydrogenation and lowers the energy barrier for C-N coupling involved in the formation of *NO2CO2. Encouragingly, with the synthesized boron-doped Cu catalysts, we achieve a high urea Faradaic efficiency exceeding 80% at a low overpotential of -0.22 V vs the reversible hydrogen electrode, along with a substantial urea production rate of 101.2 μmol h-1 cm-2. In contrast, the pristine Cu only shows a low urea selectivity (19%) and production rate (<20 μmol h-1 cm-2) under identical conditions. Furthermore, a comprehensive life-cycle assessment underscores the significance of abundant nitrate sources for urea electrosynthesis. This work introduces an effective approach for selective and efficient urea synthesis, offering valuable insights into C-N coupling and guiding the design of energy-efficient electrocatalysts for urea production.