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S-scheme heterojunction construction enhances photocatalytic hydrogen evolution

Photocatalytic hydrogen production technology represents one of the most significant approaches for addressing the energy crisis and environmental pollution. Cadmium sulfide (CdS), with its appropriate bandgap and adjustable surface structure, has been extensively utilized in photocatalytic hydrogen production.

Moreover, the quantum size effect of CdS quantum dots (QDs) enhances photocatalytic performance, while their tunable bandgap enables broader visible-light absorption. However, CdS suffers from severe photogenerated carrier recombination and is susceptible to hole-oxidation-induced photocorrosion, which significantly restricts its application in photocatalysis.

To overcome these challenges, various effective strategies have been proposed, such as morphology regulation, elemental doping, and heterostructure construction. Among these strategies, constructing an S-scheme heterojunction with a suitable semiconductor is particularly promising.

The formation of S-scheme heterojunctions allows oxidation and reduction reactions to occur at distinct locations, thereby promoting the spatial separation of photogenerated charges. Consequently, the rational design and construction of S-scheme heterostructures provide a viable pathway to enhance the photocatalytic activity of CdS.

Recently, a research team headed by Associate Professor Kang-Qiang Lu (Jiangxi University of Science and Technology) successfully designed an S-scheme heterojunction composed of CdS QDs and In₂O₃ hollow nanotubes. This design has demonstrated significantly enhanced photocatalytic hydrogen production activity.

The formation of the S-scheme heterojunction effectively suppresses photogenerated carrier recombination, thereby promoting electron separation and transfer, which in turn enhances both the photocatalytic hydrogen production activity and the stability of the composite material. The results were in Chinese Journal of Catalysis.

The S-scheme heterojunction of CdS-In₂O₃ was fabricated by growing CdS quantum dots on the surface of In₂O₃ nanotubes through an electrostatic self-assembly method. The hollow nanotube structure endows the composites with a larger specific surface area and abundant H₂ generation sites.

Moreover, the formation of the S-scheme heterostructure effectively facilitates the separation and transfer of photogenerated carriers in CdS-In₂O₃ composites. Consequently, compared to pure CdS, the photocatalytic performance of CdS-In₂O₃ composites is significantly enhanced.

In addition, the carrier transfer mechanism was investigated through in-situ X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations, thereby verifying the S-scheme heterojunction mechanism of CdS-In₂O₃ composites. Comprehensive characterizations indicate that the formation of an S-scheme heterostructure between In₂O₃ nanotubes and CdS QDs can significantly enhance the separation and migration of photogenerated carriers, consequently improving the photocatalytic performance.

This work elucidates the pivotal role of S-scheme heterojunctions in photocatalytic H₂ production and offers novel insights into the construction of effective composite photocatalysts.