Samsung Advanced Institute of Technology

Hybrid metal-semiconductor nanostructures have been utilized as attractive model catalysts for understanding photocatalytic reactions because each geometrical factor is precisely controllable. Herein, we prepared Pt-tipped CdSe nanorods and tailored their length from 10 to 30 nm. The maximum hydrogen-evolution rates by irradiation of visible light were obtained in the length of 15-20 nm for the single-tipped and 30 nm for the double-tipped nanorods. By means of time-resolved spectroscopic analysis and kinetic modeling, we revealed that the hydrogen-evolution rate was directly proportional to the amount of long-lived charge-transfer state dominated by the carrier diffusion to the metal center. As the nanorod length increased, the carrier-diffusion rate decreased, while the absorption cross-section increased. As a result, the number of carriers migrating to the metal tips was the optimum at the 15-20 nm nanorods per tip, in good agreement with our hydrogen-evolution experiments. This information provides a direct guideline to design real semiconductor-metal hybrid catalysts with a suitable ratio and distribution between distinct light-harvesting and catalytic components.