Co-reduction coupling of bicarbonate and nitrate toward efficient urea synthesis

The electrocatalytic reduction of carbon dioxide (CO₂) and different nitrogenous substances has shown a broad prospect in replacing the traditional urea synthesis process, but there are still serious challenges in mass transfer at the gas-liquid-solid interface. The conversion of bicarbonate (HCO₃^-) and nitrate (NO₃^-) into urea via the C-N coupling process under environmental conditions is a promising alternative to traditional industrial urea synthesis, which uses CO₂ as the carbon source. However, initiating the C-N coupling reaction through the adsorption and activation of HCO₃^- and NO₃^- is considerably challenging. Designing and engineering highly selective and active electrocatalysts are necessary to accelerate electrochemical urea synthesis. Herein, we constructed a Mott-Schottky heterogeneous catalyst by loading Cu nanoparticles onto WN nanosheets (Cu-WN), achieving an excellent faradaic efficiency (FE) of 15.9% and urea yield rate of 421 μg h^-1 mg_cat.^-1 at -0.3 V vs. RHE, outperforming the majority of reported electrocatalysts. Results show that the spatial charge region induced by the Mott-Schottky heterostructure facilitates the simultaneous adsorption and activation of HCO₃^- and NO₃^-, accelerating the multiple-electron transfer process. This work furnishes a promising impetus for the advancement of urea electrosynthesis via electrochemical C-N coupling under ambient conditions.