Enhanced Photocatalytic C-N Coupling by Synergistic Facet and Spin-State Modulation in Mixed-Valent WOx.

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.