A direct Z-scheme MoSi₂N₄/BlueP vdW heterostructure for photocatalytic overall water splitting

Abstract

Building novel van der Waals (vdW) heterostructures is a feasible method to expand material properties and applications. A MoSi2N4/blue phosphorus (BlueP) heterostructure is designed and investigated as a potential photocatalytic candidate by first-principle calculations. Based on the band alignment and electron transfer, MoSi2N4/BlueP exhibits the characteristics of direct Z-scheme vdW heterostructure, which is favorable for the spatial separation of photogenerated carriers and retains a strong redox capacity. Moreover, the MoSi2N4/BlueP possesses suitable band-edge positions for overall water splitting. Compared with the light absorption of two monolayer materials, the heterostructure has a stronger light absorption from the visible to ultraviolet region. The solar to hydrogen conversion efficiency can reach 21.1% for the heterostructure, which is over 3-fold and 4-fold as great as that of pristine MoSi2N4 and BlueP monolayers, respectively. All the results show that the MoSi2N4/BlueP heterostructure is a promising photocatalyst for overall water splitting, and it provides new possibilities for designing high-efficiency photocatalysts.

Novel Z-Scheme BiOM1–xIx (M = Cl, Br)/β-Bi2O3-(001) and BiOI/β-Bi2O3-(001) Heterojunction Photocatalysts with O Vacancies: A Study on the Hybrid Density Functional Approach

“…For the band alignment, the migration path of the photoexcited electrons and holes is more likely to occur along the path-1 than along the path-2 in Figure b. The photoexcited electrons in the CB of β-Bi 2 O 3 could quickly transfer toward the VB of BiOI and recombine with the photogenerated holes in the VB of BiOI because of the driving forces from the built-in electric field and Coulomb attraction between holes and electrons. − In conjunction with the smaller energy gap between the CBM of β-Bi 2 O 3 and the VBM of BiOI, the interlayer recombination probability of the photogenerated electrons and holes should be much larger than the intralayer recombination probability. The photogenerated electrons with higher reduction capacity in the CB of BiOI could be retained or have a longer lifetime, and the electron migration from the CB of BiOI to the CB of β-Bi 2 O 3 is suppressed because of the dragging forces from the built-in electric field, the extra potential barrier induced by band bending, and Coulomb repulsion between the electrons in the CB of BiOI and the electrons in the CB of β-Bi 2 O 3.…”

“…The photogenerated electrons with higher reduction capacity in the CB of BiOI could be retained or have a longer lifetime, and the electron migration from the CB of BiOI to the CB of β-Bi 2 O 3 is suppressed because of the dragging forces from the built-in electric field, the extra potential barrier induced by band bending, and Coulomb repulsion between the electrons in the CB of BiOI and the electrons in the CB of β-Bi 2 O 3. − Similarly, the photogenerated holes with higher oxidation capacity in the VB of β-Bi 2 O 3 also should have a longer lifetime in the heterojunction. − Therefore, the electrons and holes in the BiOI/β-Bi 2 O 3 can be excited easily. Remarkably, they can be separated and migrate highly effectively in space.…”

“…Then, a larger number of electron–hole pairs are generated. Because of the driving forces from the built-in electric field and Coulomb attraction as well as the smaller energy gap between the CBM of β-Bi 2 O 3 and the VBM of BiOM (28/32) I (4/32) (M = Cl, Br), the photoexcited electrons in the CB of β-Bi 2 O 3 could rapidly transfer toward the VB of BiOM (28/32) I (4/32) (M = Cl, Br) and recombine with the photogenerated holes in the VB of BiOM (28/32) I (4/32) (M = Cl, Br). − Nevertheless, the photogenerated electrons with higher reduction capacity in the CB of the BiOM (28/32) I (4/32) (M = Cl, Br) should be retained because of the dragging forces from the built-in electric field, the extra potential barrier induced from band bending, and Coulomb repulsion. − The photogenerated holes with higher oxidation capacity in the VB of β-Bi 2 O 3 also should have a longer lifetime. − The charge migration path-1 is more favorable than the path-2 in Figure . Notably, the CBM level of the BiOM (1– x ) I x (M = Cl, Br) in the heterostructures increases; furthermore, the reduction power of the electrons in the CB of the BiOM (1– x ) I x is enhanced with increasing I doping concentration.…”

“…At the same time, in Figure a, it is seen that the induced impurity level makes the optical absorption of the heterostructure intensify enormously in the visible region. Furthermore, the electrons and holes in the heterojunction BiOCl (28/32) I (4/32) (V O )/β-Bi 2 O 3 can be generated and separated more effectively. − Moreover, the electrons that gather in the CB of BiOCl (28/32) I (4/32) (V O ) have a higher reduction ability in contrast to that without the O vacancy. The projected band structure and band alignment for the heterojunction BiOBr (28/32) I (4/32) (V O )/β-Bi 2 O 3 are also displayed in Figure .…”

Exploration of Photocatalytic Overall Water Splitting Mechanisms in the Z-Scheme SnS2/β-As Heterostructure

“…Under illumination, electrons from the valence bands of two monomers are excited to the corresponding conduction bands, forming separate photogenerated electron–hole pairs. Photogenerated carriers in the staggered heterostructure generally transfer and migrate along three paths. , As shown in Figure , in path I, electrons transfer from E c of β-As to E c of SnS 2 and holes transfer from E v of SnS 2 to E v of β-As. In path II, electrons transfer from E c of β-As to E v of SnS 2 and holes transfer from E v of SnS 2 to E c of β-As.…”