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.

The Z-scheme heterostructure photocatalysts have irreplaceable advantages over other heterostructures due to their ability to separate the spatial carriers and retain strong redox ability. In this study, we explored the SnS2/β-As (β-arsenene) van der Waals heterostructure with Z-scheme properties and suitable band edge positions as a potential photocatalyst for overall water splitting. Under appropriate conditions, the hydrogen evolution reaction (HER) barrier is much closer to 0. Based on the oxidation product criteria, the SnS2/β-As heterostructure photocatalyst may generate multiple end products, including •OH, H2O2, and O2. Moreover, we screen the optimal and most possible reaction pathway OER-III under irradiation among three underlying oxygen evolution reaction (OER) mechanisms, in which the intermediate species HOOH* acts as a bridge for subsequent reactions. The solar-to-hydrogen conversion efficiency of the heterostructure can reach 17.18%. This work provides new insights into designing superior photocatalysts for overall water splitting and recognizing the OER mechanism.

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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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