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

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.