Atomistic Observation of Temperature-Dependent Defect Evolution within Sub-stoichiometric WO_3–x Catalysts

Tunable crystalline defects endow WO3–x catalysts with extended functionalities for a broad range of photo- and electric-related applications. However, direct visualization of the defect structures and their evolution mechanism is lacking. Herein, aberration-corrected and in situ transmission electron microscopy was complemented by theoretical calculations to investigate the effect of temperature on the defect evolution behavior during hydrogenation treatment. Low processing temperature (100–300 °C) leads to the occurrence of randomly distributed oxygen vacancies within WO3–x nanosheets. At higher temperatures, oxygen vacancies become highly mobile and aggregate into stacking faults. Planar defects are prone to nucleate at the surface and develop in a zigzag form at 400 °C, while treating at 500 °C promotes the growth of {200}-type stacking faults. Our work clearly establishes that the atomic configuration of the defects in WO3–x samples could be manipulated by regulating the hydrogenation temperature. This study not only expands our understanding of the structure–function relationships of sub-stoichiometric tungsten oxides but also unlocks their full potential as advanced catalysts by tuning stoichiometry in a controlled manner.