Synergistic Spatial Confining Effect and O Vacancy in WO 3 Hollow Sphere for Enhanced N 2 Reduction.

Visible-light-driven N 2 reduction into NH 3 in pure H 2 O 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 N 2 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 N 2 molecules in the inner cavity and facilitates the chemisorption of N 2 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 NH 3 generation rate of 140.08 μmol g -1 h -1 , which is 7.94 times higher than the counterpart WO 3 -bulk.