Improving the Oxygen Evolution Activity by Preparing Perylene Imide Based Z-Scheme Heterojunction

Solar water splitting is an eco-friendly technology to produce clean energy, but the water oxidation half reaction hinders the overall water splitting due to four electron transfer processes. Z-Scheme photocatalytic system could effectively promote the separation of photogenerated carriers and keep strong redox ability. However, to date, research on Z-Scheme heterojunction material for photocatalytic oxygen evolution half reaction is very limited, and the mechanism on enhancing oxygen evolution activity has never been studied in detail. In this work, for the first time the CdS/PDI Z-scheme heterojunction system with high activity for O 2 evolution was constructed. The electrons transfer pathway and photoinduced carrier separation mechanism were deeply studied. Based on the experiment and calculation results, the Fermi energy level of CdS was higher than that of PDI polymer and formed the strong built-in electric field. The direction of built-in electric field is from CdS to PDI. While under visible light illumination, the photogenerated electrons transferred along Z-scheme transfer pathway, which not only significantly increased the separation efficiency of electrons/holes but also remained the stronger oxidability of holes in PDI, thus dramatically enhance the oxygen evolution activity of PDI. The highest O 2 evolution rate on 15%CdS/PDI was 1329.2 µmol•g -1 •h -1 , and that was 1.7 times higher than that of pristine PDI under visible light illumination. Theoretical calculation results indicated that the formation of intermediate state of OOH* was the rate determining step for PDI in photocatalytic water oxidation reaction, and CdS/PDI Z-scheme heterojunction could greatly reduce the energy barrier of determining step, which is also a crucial factor for enhancement the photocatalytic oxygen evolution activity of CdS/PDI Z-scheme heterostructure