Durable and efficient urea electrosynthesis using carbon dioxide and nitrate over defect-rich In2O3 nanotubes†

Abstract

Electrochemical conversion of CO₂ and NO₃⁻ waste (EC-CO₂/NO₃⁻) 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 In₂O₃ nanotube (In₂O₃-NT) material derived from a metal–organic framework (MOF) which functions as an electrocatalyst for durable and efficient urea synthesis via EC-CO₂/NO₃⁻. The obtained In₂O₃-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 In₂O₃-NT with enriched Vo could stabilize the *CO₂NH₂ intermediate, thus accelerating the rate-determining step (RDS). The DFT simulation demonstrated that the transformation of *COOHNH₂ to *CONH₂ is the RDS for urea formation. The defect-engineered In₂O₃-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 In₂O₃-NT is highly capable of activating CO₂ and NO₃⁻ waste molecules for urea synthesis, and is conceptually versatile for other value-added chemical production methods.