Converting both nitrogen (N₂) and carbon dioxide (CO₂) into value-added urea molecules via C-N coupling reaction is a promising method to solve the problem of excessive CO₂ emissions. 

Compared with huge energy consumption industrial processes, the electrochemical urea synthesis provides an appealing route under mild conditions. However, it still faces challenges of low catalytic activity and selectivity. 

A research team led by Prof. ZHANG Guangjin from the Institute of Process Engineering (IPE) of the Chinese Academy of Sciences fabricated Bi-BiVO₄ Mott-Schottky heterostructure catalysts for efficient urea synthesis at ambient conditions. 

This work was published in Angewandte Chemie International Edition on Feb 25 (DOI: 10.1002/anie.202101275). 

The spontaneous charge transfer at the heterointerfaces promotes the formation of space-charge region. "The space-charge region not only facilitates the targeted adsorption and activation of CO₂ and N₂ molecules on the generated electrophilic/nucleophilic regions, but also effectively suppresses CO poisoning and the formation of endothermic *NNH intermediate," said Prof. ZHANG. 

The adsorbed *N₂ can promote CO₂ reduction to form CO, and then the generated CO will further react with *N₂ to produce the desirable *NCON* intermediate via electrochemical C-N coupling reaction. 

"The subsequent protonation process preferentially undergoes the alternating mechanism until the formation of urea," said Prof. ZHANG. 

The researchers used linear sweep voltammetry (LSV) to preliminarily evaluate the potential performance of urea electrosynthesis with Bi-BiVO₄ hybrids. The results showed that Bi-BiVO₄ hybrids exhibited good performance in electrocatalytic NRR (Nitrogen Reduction Reaction) and CO₂RR (CO₂ Reduction Reaction), which ensured the electrocatalytic production of urea process. 

The schematic electrocatalytic urea synthesis mechanism based on Bi-BiVO4 Mott-Schottky heterostructure synergistic effects (Image by ZHANG Guangjin and YUAN Menglei)   

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