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Visible-light-driven photocatalytic overall water splitting is deemed to be an ideal way to generate clean and renewable energy. The direct Z-scheme photocatalytic systems, which can realize the effective separation of photoinduced carriers and possess outstanding redox ability, have attracted a huge amount of interest. In this work, we have studied the photocatalytic performance of the bilayer MoSe2/HfS2 van der Waals (vdW) heterojunction following the direct Z-scheme mechanism by employing the hybrid density functional theory. Our calculated results show that the HfS2 and MoSe2 single layers in this heterojunction are used for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively. The charge transfer between the two layers brought about an internal electric field pointing from the MoSe2 layer to the HfS2 slab, which can accelerate the separation of the photoinduced electron–hole pairs and support the Z-scheme electron migration near the interface. Excitingly, the optical absorption intensity of the MoSe2/HfS2 heterojunction is enhanced in the visible and infrared region. As a result, these results reveal that the MoSe2/HfS2 heterojunction is a promising direct Z-scheme photocatalyst for photocatalytic overall water splitting.

Using hybrid density functional calculations, the influence of rotation angles on the photocatalytic performance of 2D ZnO/GaN heterostructures is explored. The results show that the bandgaps and band alignments for ZnO/GaN heterostructures can be tuned by rotation angles. Rotated ZnO/GaN heterostructures are favorable for visible light absorption. Band alignments of different rotated ZnO/GaN heterostructures are severally thermodynamically favorable for spontaneous generation of hydrogen and oxygen with the pH scope of 0–14, 3–14, 2–14, 1–14, 1–14, and 4–14. In addition, the formed built‐in electric field across ZnO/GaN heterostructure interface promotes photogenerated carrier migration and inhibits photogenerated carrier recombination. These factors make rotated ZnO/GaN heterostructures promising for visible light water splitting. The findings pay a new way to design 2D heterostructures used for photocatalytic water splitting.

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