ZnWO4-ZnIn2S4 S-scheme heterojunction for enhanced photocatalytic H2 evolution

Abstract

• The 2D ZnWO 4 -ZnIn 2 S 4 heterojunction was synthesized successfully. • The S-scheme heterojunction was identified by UPS and EPR. • The ZnWO 4 -ZnIn 2 S 4 shows enhanced photocatalytic performances in H 2 evolution. • Possible photocatalytic mechanism of our S-scheme heterojunction is proposed at last. The recombination of photogenerated electrons and holes is a crucial factor limiting photocatalytic H 2 evolution. The S-scheme ZnWO 4 -ZnIn 2 S 4 heterojunction with 2D coupling interfaces was successfully synthesized using a simple solvothermal method. An effective S-scheme interfacial charge migration route at the S-scheme heterogeneous interface was determined by energy band structure analyses (such as UPS, Mott-Schottky and XPS plots), which facilitates the separation of photoexcited carriers. It is worth noting that the optimal ZnWO 4 -ZnIn 2 S 4 composite has an H 2 evolution activity of 4925.3 μmol g −1 h −1 with favourable photostability and stability. Meanwhile, the ZnWO 4 -ZnIn 2 S 4 heterojunction exhibits the maximum optical response value (2.8 mA cm −2 ) in the initial stage, effectively promoting the separation and migration of photogenerated carriers. The establishment of the built-in electric field direction at the interface can effectively promote the space charge separation between the ZnWO 4 and ZnIn 2 S 4 nanosheets, which is favorable to the photocatalytic H 2 evolution. This work provides valuable guidance for designing S-scheme heterojunction photocatalysts composed of two n-type semiconductors for energy and environmental applications.