Synergistic Spatial Confining Effect and O Vacancy in WO₃ Hollow Sphere for Enhanced N₂ Reduction

Visible-light-driven N₂ reduction into NH₃ in pure H₂O provides an energy-saving alternative to the Haber-Bosch process for ammonia synthesizing. However, the thermodynamic stability of N≡N and low water solubility of N₂ remain the key bottlenecks. Here, we propose a solution by developing a WO_3-x hollow sphere with oxygen vacancies. Experimental analysis reveals that the hollow sphere structure greatly promotes the enrichment of N₂ molecules in the inner cavity and facilitates the chemisorption of N₂ onto WO_3-x-HS. The outer layer's thin shell facilitates the photogenerated charge transfer and the full exposure of O vacancies as active sites. O vacancies exposed on the surface accelerate the activation of N≡N triple bonds. As such, the optimized catalyst shows a NH₃ generation rate of 140.08 μmol g^-1 h^-1, which is 7.94 times higher than the counterpart WO₃-bulk.