Rationally designed WS2/C2N layered heterostructures for enhanced photocatalytic hydrogen evolution: Interface and bandgap engineering

Constructing layered heterostructured photocatalysts based on two dimensional semiconductor materials, such as transition metal dichalcogenides (TMDs) and graphitic carbon nitride (CxNy), has become a research hotspot in photocatalysis with the remarkable improvement of photoexcited charge separation efficiency. Herein, the electronic properties and photocatalytic activities of WS2/C2N bilayer and trilayer heterojunctions have been comparatively investigated using first-principles calculations. The results demonstrate that the WS2/C2N, WS2/C2N/WS2, and C2N/WS2/C2N are type-II van der Waals heterostructures, with an indirect bandgap of 1.79 eV, 1.72 eV, and 1.79 eV, respectively. Compared to WS2/C2N bilayer, the two sandwiched heterojunctions demonstrate stronger interfacial interactions, charge transfer, and visible-light absorption. The free energy calculations for redox reactions of the sandwiched heterojunctions further demonstrate high catalytic activity for hydrogen evolution reaction. More interestingly, biaxial strains can adjust the bandgap width (semiconductor -> metal) and induce the band type transition (indirect -> direct) in WS2/C2N sandwiched heterojunctions. For example, a weak stress about 1% leads to direct band gap both in type-II WS2/C2N/WS2 and C2N/WS2/C2N heterojunctions, without degrading their excellent abilities for water decomposition. This work not only provides rational strategies to design TMDs/CxNy-based photocatalysts in view of interface and bandgap engineering, but also reveals their potential applications in electronic and optoelectronic devices.

Automated summary

Constructing layered heterostructured photocatalysts based on two-dimensional semiconductor materials is a research hotspot in photocatalysis. In this study, the electronic properties and photocatalytic activities of WS2/C2N bilayer and trilayer heterojunctions were investigated. The results showed that WS2/C2N, WS2/C2N/WS2, and C2N/WS2/C2N are type-II van der Waals heterostructures with different bandgaps. The sandwiched heterojunctions demonstrated stronger interfacial interactions, charge transfer, and visible-light absorption, and exhibited high catalytic activity for hydrogen evolution reaction. Biaxial strains can also adjust the bandgap width and induce band type transition in WS2/C2N sandwiched heterojunctions. This work provides strategies for designing TMDs/CxNy-based photocatalysts and reveals their potential applications in electronic and optoelectronic devices.