Durable and efficient urea electrosynthesis using carbon dioxide and nitrate over defect-rich InO nanotubes

Electrochemical conversion of CO 2 and NO 3 − waste (EC-CO 2 /NO 3 − ) into valuable urea is a promising method for fertilizer production and environmental remediation, but its practical application is currently limited by the low efficiency of electrocatalytic processes. Here, we report a novel In 2 O 3 nanotube (In 2 O 3 -NT) material derived from a metal-organic framework (MOF) which functions as an electrocatalyst for durable and efficient urea synthesis via EC-CO 2 /NO 3 − . The obtained In 2 O 3 -NT-500 with a porous structure and rich oxygen vacancies (Vo) is more conducive to the target reaction system, reaching a urea formation rate of 1441 μg mg cat −1 h −1 with a high faradaic efficiency of 60.3%, exhibiting the top-level performance toward urea synthesis via the current route. In situ attenuated total reflection Fourier transform infrared spectroscopy verified that In 2 O 3 -NT with enriched Vo could stabilize the *CO 2 NH 2 intermediate, thus accelerating the rate-determining step (RDS). The DFT simulation demonstrated that the transformation of *COOHNH 2 to *CONH 2 is the RDS for urea formation. The defect-engineered In 2 O 3 -NT catalyst significantly lowers the energy barrier for this step, thus boosting the overall efficiency of urea synthesis. This work provides an example showing that the defect engineering of In 2 O 3 -NT is highly capable of activating CO 2 and NO 3 − waste molecules for urea synthesis, and is conceptually versatile for other value-added chemical production methods. A defect-rich In 2 O 3 electrocatalyst is highly durable and efficient for sustainable urea synthesis via co-reduction of CO 2 /NO 3 − under mild conditions.