DFT investigation on two-dimensional GeS/WS2 van der Waals heterostructure for direct Z-scheme photocatalytic overall water splitting

Highlights: • The GeS/WS₂ heterojunction is a candidate for the direct Z-scheme photocatalysts. • The interface Z-scheme electron transfer is investigated through DFT. • The internal electric field can promote the separation of charge carriers. • Reducing the interfacial distance could improve the catalytic activity. Recently, extensive attention has been paid to the direct Z-scheme systems for photocatalytic water splitting where carriers migrate directly between the two semiconductors without a redox mediator. In the present work, the electronic structure and related properties of two-dimensional (2D) van de Waals (vdW) GeS/WX₂ (X = O, S, Se, Te) heterojunction are systematically investigated by first-principles calculations. Our results demonstrate that, the GeS/WS₂ heterojunction could form a direct Z-scheme system for photocatalytic water splitting, whereas the GeS/WX₂ (X = O, Se, Te) can't, because of their respective unsuitable electronic structures. For the GeS/WS₂ heterojunction, the GeS and WS₂ monolayers serve as photocatalysts for the hydrogen evolution reactionand oxygen evolution reaction, respectively. The internal electric field induced by the electron transfer at the interface can promote the separation of photo-generated charge carriers and formation of the interface Z-scheme electron transfer. Remarkably, the designed GeS/WS₂ heterojunction not only enhances the hydrogen production activity of GeS and the oxygen production ability of WS₂ but also improves the light absorption of the two monolayers by reducing the band gaps. Moreover, it is found that narrowing the interlayer distance could enhance the internal electric field, improving the photocatalytic ability of the vdW heterojunction. This work provides fundamental insights for further design and preparation of emergent metal dichalcogenide catalysts, beneficial for the development in clean energy.