Triplet-Triplet Annihilation Upconversion for Photocatalytic Hydrogen Evolution.

The solar generation of hydrogen by water splitting provides a promising path for renewable hydrogen production and solar energy storage. Upconversion of low-energy photons into high-energy photons constitutes a promising strategy to enhance the light harvesting efficiency of artificial hydrogen production systems. In the present study, upconversion micelles are integrated with Cd0.5 Zn0.5 S to construct solar energy conversion systems. The upconversion micelle is employed to upconvert red photons to cyan photons. Cd0.5 Zn0.5 S is sensitized by upconverted cyan light to produce hydrogen, but not by incident red light without triplet-triplet annihilation upconversion (TTA-UC). The performance of the upconversion photocatalytic system was dramatically affected by the concentration of Cd0.5 Zn0.5 S and the irradiation intensity. This novel system was able to produce about 2.3 μL hydrogen after 5 h of red light (629 nm) irradiation (2.4 mW cm-2 ). The present study provides a candidate for applications using low-energy photons for solar hydrogen generation.