Grain boundary-mediated electrocatalytic C–N coupling for urea synthesis from CO2 and NOx

Abstract

Electrocatalytic urea synthesis from CO₂ and NO_x provides a sustainable route for simultaneous chemical production and pollutant utilization. Although grain-boundary engineering has emerged as a promising strategy for promoting sluggish C–N coupling, why a grain-boundary-rich defective microenvironment can regulate selective urea formation remains insufficiently understood. Here, we employed TiO₂ as a model catalyst and constructed polycrystalline grain boundaries to improve both the activity and selectivity for urea synthesis. Trace Fe species served mainly as structural inducers for grain-boundary formation and promoted the generation of oxygen-vacancy-related defective regions. Operando electrochemical impedance spectroscopy revealed enhanced interfacial charge transfer and faster interfacial response, while operando infrared spectroscopy tracked the evolution of carbon- and nitrogen-containing surface species and supported the formation of the *OCNO intermediate during selective C–N coupling. The results show that the grain-boundary-rich defective microenvironment facilitates interfacial activation and selective C–N coupling during CO₂ and NO_x co-reduction. This work highlights the important role of grain-boundary-rich defective structures in understanding why grain boundaries can promote selective electrocatalytic urea synthesis.