Phosphorene-Based van der Waals Heterojunction for Solar Water Splitting

As a clean and renewable future energy source, hydrogen fuel can be produced via solar water splitting. Two-dimensional (2D) black phosphorene (black-P) can harvest visible light due to the desirable band gap, which promises it as a metal-free photocatalyst. However, black-P can be only used to produce hydrogen since the oxidation potential of water locates lower than the position of the valence band maximum. To improve the photocatalytic performance of black-P, here, using black-P and blue phosphorene (blue-P) monolayers, we propose a 2D van der Waals (vdW) heterojunction. Theoretical results, including the band structures, density of states, Bader charge population, charge density di erence, and optical absorption spectra, clearly reveal that the visible light absorption ability is obviously improved, and the band edge alignment of the proposed vdW heterojunction displays a typical type-II feature to effectively separate the photogenerated carriers. At the same time, the built-in interfacial electric field prevents the electron-hole recombination. These predictions suggest that the examined phosphorene-based vdW heterojunction is an efficient photocatalyst for solar water splitting.

g-C3N4/SnS2 Heterostructure： a Promising Water Splitting Photocatalyst

Graphite-like carbon nitride （g-C3N4） based heterostrutures has attracted intensive attention due to their prominent photocatalytic performance. Here, we explore the g-CaN4/SnS2 coupling effect on the electronic structures and optical absorption of the proposed g-CaN4/SnS2 heterostructure through performing extensive hybrid functional calculations. The obtained geometric structure, band structures, band edge positions and optical absorptions clearly reveal that the g-C3N4 monolayer weakly couples to SnS2 sheet, and forms a typical van der Waals heterojunction. The g-C3N4/SnS2 heterostructure can effectively harvest visible light, and its valence band maximum and conduction band minimum locate in energetically favorable positions for both water oxidation and reduction reactions. Remarkably, the charge transfer from the g-C3N4 monolayer to SnS2 sheet leads to the built-in interface polarized electric field, which is desirable for the photogenerated carrier separation. The built-in interface polarized electric field as well as the nice band edge alignment implys that the g-CaN4/SnS2 heterostructure is a promising g-CaN4 based water splitting photocatalyst with good performance.

Two-Dimensional GaTe/Bi2Se3 Heterostructure:a Promising Direct Z-scheme Water Splitting Photocatalyst

Among various photocatalytic materials,Z-scheme photocatalysts have drawn tremendous research interest due to high photocatalytic performance in solar water splitting.Here,we perform extensive hybrid density functional theory calculations to explore electronic structures,interfacial charge transfer,electrostatic potential profile,optical absorption properties,and photocatalytic properties of a proposed two-dimensional(2D)small-lattice-mismatched GaTe/Bi2Se3 heterostructure.Theoretical results clearly reveal that the examined heterostructure with a small direct band gap can effectively harvest the broad spectrum of the incoming sunlight.Due to the relative strong interfacial built-in electric field in the heterostructure and the small band gap between the valence band maximum of Ga Te monolayer and the conduction band minimum of Bi2Se3 nanosheet with slight band edge bending,these photogenerated carriers transfer via Z-scheme pathway,which results in the photogenerated electrons and holes effectively separating into the Ga Te monolayer and the Bi2Se3 nanosheet for the hydrogen and oxygen evolution reactions,respectively.Our results imply that the artificial 2D GaTe/Bi2Se3 is a promising Z-scheme photocatalyst for overall solar water splitting.