| Summary: | Visible-light-driven N<sub>2</sub> reduction into NH<sub>3</sub> in pure H<sub>2</sub>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<sub>2</sub> remain the key bottlenecks. Here, we propose a solution by developing a WO<sub>3−x</sub> hollow sphere with oxygen vacancies. Experimental analysis reveals that the hollow sphere structure greatly promotes the enrichment of N<sub>2</sub> molecules in the inner cavity and facilitates the chemisorption of N<sub>2</sub> onto WO<sub>3−x</sub>-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<sub>3</sub> generation rate of 140.08 μmol g<sup>−1</sup> h<sup>−1</sup>, which is 7.94 times higher than the counterpart WO<sub>3</sub>-bulk.
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