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.

Manipulating the valley degree of freedom is an important target of valleytronics development, which provides remarkable opportunities for both fundamental research and practical applications. Here, based on first-principles calculations, we demonstrate the intrinsic valley-polarized quantum anomalous Hall effect in a monolayer ferrovalley material: Janus VSiGeN4, of which the edge states are chiral-spin-valley locking. Furthermore, a small tensile or compressive strain can drive phase transition in the material from the valley-polarized quantum anomalous Hall state to the half-valley-metal state. With the increase in the strain, the material turns into a ferrovalley semiconductor with the valley anomalous Hall effect. The origin of the phase transition is the sequent band inversion of the V d orbital at the K valleys. Moreover, we find that phase transition causes the sign reversal of the Berry curvature and induces different polarized light absorption in different valley states. Our work provides an ideal material platform for practical applications and experimental exploration of the interplay among topology, spintronics, and valleytronics.

An intrinsic out-of-plane electronic field can inhibit the recombination of photogenerated carriers in two-dimensional (2D) polar materials. On the other hand, a direct Z-scheme constructed from 2D van der Waals heterostructure can not only effectively separate photogenerated carriers, but also can retain robust redox abilities. g-C6N6/InP, a direct Z-scheme heterostructure with a polarized material is successfully designed, which are verified to be available for overall water splitting through first-principles calculations. Due to the synergistic effects of intrinsic electric field and a direct Z-scheme heterostructure, hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) can simultaneously take place on the g-C6N6 and InP monolayer, respectively. The predicted solar-to-hydrogen (STH) efficiency can reach up to 21.69%, which breaks the conventional theoretical limit of ~18%. The suitable direction of intrinsic electronic field in the polar material can enhance the photogenerated carrier migration and redox abilities for both HER and OER. Based on these findings, the g-C6N6/InP vdW heterostructure can provide a new perspective for finding higher-efficiency Z-scheme photocatalysts with polar materials for overall water decomposition.

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IInspired by natural photosynthesis, two-dimensional van der Waals (vdW) heterostructures are considered as promising photocatalysts for solar-driven water splitting and attract ever-growing interest. A type-II vdW hetero-photocatalyst (CdTe/B4C3) integrated the...