Sequestering High-Energy Electrons to Facilitate Photocatalytic Hydrogen Generation in CdSe/CdS Nanocrystals

The photocatalytic H2O splitting activities of CdSe and CdSe/CdS core/shell quantum dots are contrasted. CdSe/CdS core/shell quantum dots constructed from 4.0 nm CdSe quantum dots are shown to be strongly active for visible-light-driven photocatalytic H-2 evolution in 0.1 M Na2S/Na2SO3 solution with a turnover number of 9.94 after 5 h at 103.9 mu mol/h. CdSe quantum dots themselves are only marginally active in 0.1 M Na2S/Na2SO3 solution with a turnover number of 1.10 after 5 h at 11.53 mu mol/h, while CdSe quantum dots in pure H2O are found to be completely inactive. Broad-band transient absorption spectroscopy is used to elucidate the mechanisms that facilitate the enhancement in the CdSe core/shell quantum dots, which is attributed to passivation of surface-deep trap states with energies lying below the reduction potential necessary for H2O reduction. Thus, surface trapping dynamics and energetics can be manipulated to dictate the photocatalytic activities of novel CdSe quantum dot based photocatalytic materials.