Direct Z-Scheme LiMXY/GaZ (M = Al, Ga, In; X = S, Se; Y = Se, Te; Z = P, As) van der Waals Heterostructures: Promising Photocatalysts with High Solar-to-Hydrogen Efficiency for Water Splitting

Two-dimensional (2D) direct Z-scheme heterostructures are regarded as highly effective photocatalysts for overall water splitting, owing to their capability to efficiently separate photogenerated charge carriers and their enhanced redox characteristics. Here, based on first-principles calculations, we propose van der Waals LiMXY/GaZ (M = Al, Ga, In; X = S, Se; Y = Se, Te; Z = P, As) heterostructures and show that LiAlSTe/GaP, LiGaSTe/GaP, LiInSTe/GaAs, and LiGaSe 2 /GaAs are type-II heterostructures with a direct Z-scheme charge transfer mechanism. The stability of these four heterostructures is verified by ab initio molecular dynamic simulations, binding energy, and phonon dispersion calculations. The HSE06 (PBE) bandstructures reveal that the four studied heterostructures are direct semiconductors with bandgaps in the range of 1.52–1.96 eV (0.93–1.28 eV). The plots of band alignment show that in all investigated heterostructures, the conduction band minimum and valence band maximum straddle the redox potentials of water. The large oxygen and hydrogen overpotentials lead to a remarkable solar-to-hydrogen efficiency (up to 30.5%) in the studied heterostructures. In all the examined heterostructures, the absorption coefficient in the visible spectrum attains a peak value of 2 × 10 5 cm 1, significantly surpassing the coefficients found in other Z-scheme heterostructures. A significant difference is observed between the electron mobility (ranging from 2095.8 to 4962.2 cm 2 V 1 s 1 ) and the hole mobility (ranging from 176.02 to 1889.6 cm 2 V 1 s 1 ), resulting in a lower recombination rate in the proposed heterostructures. These features affirm that the direct Z-scheme LiAlSTe/GaP, LiGaSTe/GaP, LiInSTe/GaAs, and LiGaSe 2 /GaAs heterostructures hold significant potential in the field of photocatalysis for overall water splitting.