Photocatalytic water splitting system using particulate semiconductor materials is a promising strategy for converting solar energy into hydrogen and oxygen. In particular, visible-light-driven ‘Z-schematic’ printable photocatalyst sheets are cost-effective and scalable systems. However, little is known about the fundamental photophysical processes, which are key to explain and promote photoactivity. Here, we applied the pattern-illumination time-resolved phase microscopy (PI-PM) for the printed photocatalyst sheet, composed of Mo-doped BiVO4 (BVOM) and Rh-doped SrTiO3 (STOR), indium tin oxide (ITO) as an electron mediator, to investigate photo-generated charge carrier dynamics. Using the PI-PM, we successfully observed for the first time the position- and structure-dependent charge carrier behavior, including visualization of the active/inactive sites in the sheet, under the visible-light irradiation via the time sequence images and the clustering analysis. We have extended our measurements of the refractive index change for a local mapping of the transient responses of photo-excited charge carriers, PI-PM method. By illuminating a pattern of light, the sequence of images due to the refractive index change was obtained, and the image quality was recovered by the image recovery calculation techniques. The local responses of charge carriers were categorized by the spectral clustering method and found the hidden local responses of the non-radiative exciton relaxation for higher pump intensities. These findings have motivated us to apply this combination of PI-PM and clustering analysis method for one of the most promising Z-scheme water splitting materials, BiVO4:Mo/SrTiO3:Rh with a conductive colloidal binder (ITO), as a printable photocatalyst sheet with a conductive colloidal binder (ITO) prepared by the printing method. We could visualize the spatially-resolved photocatalytic activity by the categorization of the charge carrier behaviors. This new methodology could detect the real active and inactive sites in the photocatalytic device and will support the optimization of the active structure of the photocatalyst.

Charge carrier mapping for Z-scheme photocatalytic water splitting sheet by categorization of microscopic time-resolved image sequence

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.