Green Urea Synthesis from CO₂ and Nitrogenous Small Molecules via Electrocatalysis and Photocatalysis

Urea is an important and widely consumed compound in agriculture and pharmaceutical industries. Electrocatalytic and photocatalytic approaches enable green urea synthesis from CO₂ and nitrogenous small molecules (N₂, NO₃ ^-, NO₂ ^-, and NO), offering electron-driven parallel routes that are alternative to Bosch-Meiser process with net-zero emission potential. Although considerable efforts have achieved significant progress, current green urea synthesis is still far from the requirements of practical production due to sluggish reaction kinetics and low efficiency and selectivity of urea. Developing advanced catalysts and catalytic system is crucial for practical green urea synthesis. Therefore, in this review, the fundamentals of urea synthesis, covering the electrocatalytic and photocatalytic processes, thermodynamic and kinetic considerations, C-N coupling mechanism, and urea detection methods are introduced. Then, the pivotal role of the catalytic center in C-N coupling and recent breakthroughs in strategies for catalysts and reaction system design are summarized. Finally, potential directions for catalytic system optimization, standardization of product analysis, and scale-up from laboratory to industry are proposed to guide future research on green urea synthesis.