New gallium chalcogenides/arsenene van der Waals heterostructures promising for photocatalytic water splitting

Single two-dimensional (2D) GaS and GaSe were studied as photocatalysts, yet the overall performance is limited by the low optical absorption and inefficient separation of photogenerated electron-hole pairs. Constructing van der Waals (vdW) heterostructures is an ideal way to overcome the deficiency of single 2D gallium chalcogenides. This work unravels that gallium chalcogenides/arsenene (GaX/As, X = S, Se) are the promising vdW heterostructures that show significantly improved photocatalytic performance by means of first-principles calculations. The GaX/As heterostructures possess suitable band alignment and bandgap satisfying the requirements for photocatalysts. Contrary to the pristine monolayers, the Se_0.5GaS_0.5/As and S_0.5GaSe_0.5/As heterostructures undergo indirect-direct bandgap transition by varying the interlayer distances; moreover, they exhibit high carrier mobility (∼2000 cm² V⁻¹ s⁻¹ for electrons) and transport anisotropy, efficiently facilitating the migration and separation of photogenerated electron-hole pairs. Finally, all GaX/As heterostructures show significantly enhanced optical absorption beyond the isolated GaX monolayers under visible-light irradiation. These extraordinary properties render GaX/As heterostructures as competitive photocatalysts for water splitting to produce hydrogen.