Integration of 2D layered CdS/WO3 S-scheme heterojunctions and metallic Ti3C2 MXene-based Ohmic junctions for effective photocatalytic H2 generation

The rapid recombination of photo-generated electron-hole pairs, insufficient active sites, and strong photocorrosion have considerably restricted the practical application of CdS in photocatalytic fields. Herein, we designed and constructed a 2D/2D/2D layered heterojunction photocatalyst with cascaded 2D coupling interfaces. Experiments using electron spin resonance spectroscopy, ultraviolet photoelectron spectroscopy, and in-situ irradiation X-ray photoelectron spectroscopy were conducted to confirm the 2D layered CdS/WO3 step-scheme (S-scheme) heterojunctions and CdS/MX ohmic junctions. Impressively, it was found that the strong interfacial electric fields in the S-scheme heterojunction photocatalysts could effectively promote spatially directional charge separation and transport between CdS and WO3 nanosheets. In addition, 2D Ti3C2 MXene nanosheets with a smaller work function and excellent metal conductivity when used as a co-catalyst could build ohmic junctions with CdS nanosheets, thus providing a greater number of electron transfer pathways and hydrogen evolution sites. Results showed that the highest visible-light hydrogen evolution rate of the optimized MX-CdS/WO3 layered multi-heterostructures could reach as high as 27.5 mmol/g/h, which was 11.0 times higher than that of pure CdS nanosheets. Notably, the apparent quantum efficiency reached 12.0% at 450 nm. It is hoped that this study offers a reliable approach for developing multifunctional photocatalysts by integrating S-scheme and ohmic-junction built-in electric fields and rationally designing a 2D/2D interface for efficient light-to-hydrogen fuel production.