A visualizable means for verifying the manner of charge transfer in WO3-based type-II heterostructures

Abstract

Research into photocatalytic mechanisms and charge carrier transfer is of vital significance. For type-II heterostructures containing WO₃, a visualizable means is proposed for the first time for verifying the manner of charge transfer via observing the photochromism of WO₃. The accuracy of this visualizable means is evidenced through corresponding characterization, such as XPS and OCP. In addition, photocatalytic H₂ evolution as a supporting proof is studied to prove the manner of charge transfer owing to the inactivity of WO₃. If the charge transfer pathway principally follows a conventional type-II manner, the heterostructure will change color from yellow to a dark color and show lower activity compared with the individuals. However, if the charge transfer primarily follows a Z-scheme mechanism, the color won't show a noticeable change but much higher activity will be exhibited than that by the individual components. CdS–WO₃ and ZnIn₂S₄–WO₃ (ZIS–WO₃) are used as examples to verify the universality of this method and exclude the impact of the crystal phase of WO₃ on photochromism.