Boosting urea electrosynthesis on In(OH)₃ hollow nanospheres via defect and edge site engineering

Electrosynthesis of urea from CO₂ and nitrate is an eco-friendly and sustainable approach. The current catalysts still face significant challenges such as low density of active sites, limited mass transfer efficiency and insufficient regulation of electronic structure. In this study, a high-performance hollow nanosphere-structured V_O-In(OH)₃ was prepared through defect engineering and edge site engineering. It demonstrated remarkable urea electrosynthesis performance of 2335.37 μg·h⁻¹·mg_cat.⁻¹ production rate and up to 81.08% Faradaic efficiency, which are significantly better than the traditional In(OH)₃. The nano-hollow structure synergically promotes the electrolyte mass transfer process. The enhancing mechanisms of edge sites and oxygen vacancies on exposed (100) facet were explored by density functional theory (DFT) calculations, in-situ attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy and Raman spectroscopy. The electron reconstruction around the unsaturated In atom increases the carrier concentration and optimizes the charge transfer efficiency by strengthening the orbital coupling of the active sites and key intermediate (*CO₂NH₂). Both edge sites and oxygen vacancies benefit the protonation key step of *CO₂NH₂ intermediate to *COOHNH₂. Through the collaborative of edge sites and defect engineering, this work proposes an innovative catalyst design strategy for enhanced urea electrosynthesis, and promotes the development for resource utilization of carbon dioxide and nitrate wastewater.