Remodeling Interfacial Hydrogen-Bond Network Via Crystal Facet Control for Efficient Urea Electrosynthesis

The electrochemical coreduction of CO2 and nitrate for urea synthesis is hindered by competing side reactions due to conflicting proton demands. Here, using facet-engineered Cu2O nanocrystals, we find that the (100) facet achieves a urea yield of 84.4 mmol h-1 gcat-1, 3.2- and 3.7-fold those of the (111) and (110) facets, and a Faradaic efficiency of 32%, which outperforms the 11% and 8% on the other two facets. By integrating in situ Raman spectroscopy with ab initio molecular dynamics simulations, we elucidate that the (100) facet preferentially accumulates hydrated K+ cations to reorient interfacial water into a constrained "one-H-down" conformation. This restructuring limits proton availability to suppress parasitic H2 and NH3 formation, while the K+-rich field stabilizes *CO and *NO intermediates via electrostatic effects. The combined action of proton restriction and intermediate stabilization lowers the kinetic barrier for C-N coupling and selectively promotes urea formation.