Size Effects on Photocatalytic H2 Generation with CdSe/CdS Core-Shell Nanocrystals

CdSe/CdS core-shell nanocrystals with controlled CdS shell thickness and CdSe core size were synthesized for several different values of these two parameters. The particles in aqueous dispersion were in situ decorated with Ni nanoparticles and evaluated for photocatalytic hydrogen generation capacity. The highest H-2 production quantum yield at 457 nm illumination was 4.7%, while at 530 nm it rose to 9.1%. We have found that ensuring equal absorption at illumination wavelength the H-2 formation rate increases with the shell thickness, but decreases with the increasing core size. Interestingly, the same trend was observed for the photoluminesce quantum yield and lifetime for samples without Ni decoration, suggesting that they reflect the balance between charge transfer and avoidance of recombination sites which is crucial for photocatalysis with semiconductor nanocrystals. Moreover, the core-shell nanocrystals constitute a very convenient model system in which the charge carrier dynamics in photocatalytic applications can be studied. In comparison with well-known CdSe/CdS dot-in-rod structures they are less efficient at blue illumination, but they allow for significant extension of the usable absorption range.