Synergy of Cd Doping and S Vacancies in CdxZn1–xIn2S4 Hierarchical Nanotubes for Highly Improved Visible-Light-Driven H2 Evolution

Photocatalytic water splitting over semiconductors is believed as a promising avenue to obtain H₂ fuel from renewable solar energy. However, developing highly active and non-noble-metal photocatalysts for H₂ evolution is still quite challenging to date. In this work, by constructing nanosheet-based nanotubes with Cd-doping and S vacancies, a highly improved visible-light-driven H₂ production for ZnIn₂S₄ is achieved. Unlike nanoflowers aggregated with nanosheets, the nanosheet-assembled hierarchical nanotubes allow multiple scattering and reflection of incident light within the interior space, leading to an enhanced light-harvesting efficiency. Together with the benefits from Cd doping and S-vacancy engineering, including narrowed band gaps, efficient transmission and separation of charge carriers, abundant catalytically active sites, heightened photo-stability and photo-electron reduction capacity, as well as a strong electrostatic attraction to protons, the synthesized S-deficient Cd_xZn_1-xIn₂S₄ hierarchical nanotubes exhibit an extraordinary photocatalytic H₂ evolution capability under visible-light irradiation, delivering an outstanding H₂-generation activity of 28.99 mmol·g^-1·h^-1 (corresponding to an apparent quantum yield of 37.1% at 400 nm), which is much superior to that of Cd_xZn_1-xIn₂S₄ nanoflowers, Pt-loaded ZnIn₂S₄ nanotubes, and most ever reported ZnIn₂S₄-based photocatalysts. Our study could inspire the development of low-cost and high-performance photocatalysts via rational structural design and optimization.