Enhanced Photocatalytic C–N Coupling by Synergistic Facet and Spin-State Modulation in Mixed-Valent WO x

Abstract Urea is an essential chemical widely used in agriculture and consumer products, yet its conventional Bosch–Meiser synthesis is energy-intensive and carbon-intensive. Photocatalytic urea synthesis from N2, CO2, and H2O offers a sustainable alternative, but efficient C–N coupling is fundamentally limited by the trade-off between intermediate stability and surface migration needed for efficient C–N coupling processes. Strong adsorption of intermediates limits diffusion, whereas weak adsorption causes premature desorption, restricting the C–N coupling efficiency. Facet and spin-state engineering provide a promising route to balance intermediate stabilization, mobility, and interfacial charge transfer. Herein, we prepared oxygen-deficient WOx (x = 2.33–2.90) photocatalysts, including nanorods (WO2.33(100)) and nanosheets (WO2.90(001)), by a facile hydrothermal and plasma-treatment method. WO2.33(100) delivered a high photocatalytic urea production rate of 1451.38 μg g–1 h–1 under UV irradiation (λ = 365 nm) in a microflow reactor, representing a 3.2-fold enhancement over WO2.90(001) and ranking among the most efficient urea-synthesis photocatalysts reported to date. Mechanistic studies, including isotope labeling, in situ ATR-FTIR, and DFT calculations, reveal that facet-confined oxygen vacancies stabilize low-spin WIII (d3) centers, which simultaneously optimize N2 adsorption while preserving the surface mobility of *NO intermediates, thereby enabling efficient C–N coupling. This work establishes a facet-confined oxygen-vacancy strategy for spin-state regulation of surface intermediates and C–N coupling pathways, providing a general strategy for improved photocatalytic urea synthesis for smart agriculture.