MoSSe/Hf(Zr)S₂ heterostructures used for efficient Z-scheme photocatalytic water-splitting

Direct Z-scheme water-splitting is a promising route to enhancing the photocatalytic performance due to the effective separation of photogenerated carriers while simultaneously preserving the strong oxidation activity of holes and reduction activity of electrons. In this work, the MoSSe/XY₂ (X = Hf, Zr; S, Se) heterostructures (HSs) with different contacts are proposed for Z-scheme photocatalytic water-spitting by first principles calculation. The separation of photogenerated carriers for HfSe₂/SMoSe and ZrSe₂/SMoSe HSs is limited by the type-I band alignment, while the hydrogen production ability of HfSe₂/SeMoS and ZrSe₂/SeMoS HSs is limited by the lower conduction band edge positions relative to the water reduction potential. The HfS₂/SMoSe, HfS₂/SeMoS, ZrS₂/SMoSe, and ZrS₂/SeMoS HSs are direct Z-scheme water-splitting photocatalysts with the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) occurring at the Hf(Zr)S₂ layer and MoSSe layer, respectively. More excitingly, the S (or Se) vacancies effectively lower the HER overpotentials. Besides, the solar-to-hydrogen efficiencies are 6.1%, 5.9%, 6.4%, and 6.3% for HfS₂/SMoSe, HfS₂/SeMoS, ZrS₂/SMoSe, and ZrS₂/SeMoS HSs, respectively. This work paves the way for designing highly efficient overall water-splitting photocatalysts using 2D materials.