Promoting Electrocatalytic\nReduction of CO<sub>2</sub> and Nitrate to Urea on N‑Doped\nPorous Hollow Carbon Spheres

The electrocatalytic coreduction of CO<sub>2</sub> and\nnitrate\nis a green method for urea synthesis, mitigating CO<sub>2</sub> emission\nand nitrate contamination. However, its slow kinetics and high energy\nbarrier result in a poor urea production performance. Herein, we reported\nN-doped porous hollow carbon spheres (N-PHCS) for promoting CO<sub>2</sub> and nitrate conversion to urea via nanoconfinement and N-doping\nfrom both reaction kinetics and thermodynamics. A high urea yield\nof 12.0 mmol h<sup>–1</sup> g<sub>cat</sub><sup>–1</sup> with Faradaic efficiency of 19.1% was achieved on N-PHCS at −1.0\nV (vs Ag/AgCl), which was comparable to or even higher than those\nof metal-based electrocatalysts reported. The experimental and theoretical\ncalculation results revealed that carbon spheres with an appropriate\ninterior void and pore size were favorable for confining reactants\nand intermediates to accelerate urea production, while N-doping can\nreduce the energy barrier for urea synthesis. By regulating the microstructure\nand N doping of N-PHCS, it showed a superior performance for urea\nelectrosynthesis. The energy favorable pathway for urea synthesis\nwas through the C–N coupling reaction of *NO and *CO, and pyridinic\nN can reduce the reaction energy barrier.