Exceptional Catalytic Nature of Quantum Dots for Photocatalytic Hydrogen Evolution without External Cocatalysts

The catalytic nature of semiconducting quantum dots (QDs) for photocatalytic hydrogen (H-2) evolution can be thoroughly aroused, not because of coupling with external cocatalysts, but through partially covering controlled amount of ZnS shell on the surface. Specifically, CdSe QDs, with an optimal coverage of ZnS (approximate to 46%), can produce H-2 gas with a constant rate of approximate to 306.3 +/- 21.1 mu mol mg(-1) h(-1) during 40 h, thereby giving a turnover number of approximate to(4.4 +/- 0.3) x 10(5), which is approximate to 110-fold to that of unmodified CdSe QDs under identical conditions. The performance of H-2 evolution is comparable to or even better than the commonly used external cocatalysts, e.g., metal complexes, noble metals assisted photosystems. Mechanistic insights indicate that the dramatically enhanced activity and stability of bare QDs for photocatalytic H-2 production are derived from (i) inhibiting exciton annihilation at trap states, (ii) preventing the photo-oxidation of core frameworks, and (iii) retaining tunneling efficiencies of photo generated electrons and holes to reactive sites with partial ZnS coverage.