Efficient Urea Electrosynthesis by Encapsulating Cu and ZnO Nanoparticles in Carbon Nanotubes

Electrocatalytic reduction of CO₂ and $N{O}_3^{-}$ offers a clean and sustainable alternative to urea production. However, urea electrosynthesis still suffers from low efficiency due to insufficient active sites and low coverage of intermediates for C-N coupling. Herein, Cu and ZnO nanoparticles encapsulated in carbon nanotubes (CuZnO@CNT) were designed to enhance urea electrosynthesis via the nanoconfinement effect and dual active sites. CuZnO@CNT was efficient for urea electrosynthesis with a high Faradaic efficiency of 32.2% and a urea yield of 1210.7 μg h^-1 mg_cat^-1 at a relatively low overpotential. It exhibited significantly enhanced urea yield and efficiency compared with Cu and ZnO nanoparticles loaded on the CNTs surface. Finite element simulations and in situ spectra revealed the enriched reactants and intermediates inside the nanotubes and the rapid formation of *CO and *NH₂ intermediates on CuZnO@CNT. Its Cu was favorable for $N{O}_3^{-}$ reduction, while its ZnO could serve as active sites for both CO₂ and $N{O}_3^{-}$ reduction. The synergistic effects of dual sites and the nanoconfinement effect contributed to its superior performance for C-N coupling.