To overcome current serious energy and environmental issues, photocatalytic water splitting holds great promise because it requires only solar energy as an energy input to produce hydrogen. In this work, based on first-principle calculations, we studied the van der Waals heterostructure formed by PtS₂ and arsenene (Are) monolayers that were successfully synthesized on a large scale at high quality. From an analysis of the migration paths of photoinduced electrons and holes, a direct Z-scheme photocatalytic mechanism is demonstrated in this heterostructure. Furthermore, the PtS₂/Are direct Z-scheme heterostructure has decent band edge positions to promote the redox reaction to decompose water at pH 0. The interfacial charge difference and potential drop are presented, which further support the formation of a direct Z-scheme photocatalyst. More importantly, the PtS₂/Are heterostructure has quite high solar-to-hydrogen (STH) efficiency (49.32%), significantly enhanced compared with isolated PtS₂ (12.67%) or Are (10.34%) monolayers. This direct Z-scheme PtS₂/Are heterostructure with excellent STH efficiency suggests its promising application as a photocatalyst for water splitting.

Two-dimensional van der Waals (vdW) heterostructures were constructed using MoSSe and XN (X = Ga, Al) via density functional calculations to serve as water splitting photocatalysts. Both the MoSSe/GaN and MoSSe/AlN heterostructures are energetically, dynamically and thermally stable. Interestingly, they exhibited type-II band structures, indicating the ability to continuously separate photogenerated electrons and holes. They also have appropriate band edge positions for redox reaction potentials of water splitting at pH 0. Remarkably, the MoSSe/GaN vdW heterostructure possessed excellent carrier mobility for holes along both the transport directions. Besides, the charge transfer between the MoSSe and XN layers induced a strong built-in electric field, which further separated the photogenerated carriers. In addition, the MoSSe/GaN and MoSSe/AlN vdW heterostructures exhibit good optical absorption ability toward solar irradiation. All these excellent properties render the MoSSe/GaN and MoSSe/AlN heterostructures are high-efficiency photocatalysts for water splitting.