Boosting photocatalytic hydrogen evolution via triplet–triplet annihilation upconversion

To enhance the light-harvesting ability of photocatalytic splitting water system, triplet–triplet annihilation upconversion (TTA-UC) is integrated with photocatalysis directly for the first time via a detergent-free ternary toluene/isopropanol/water microemulsion system. TTA-UC pairs containing PtOEP/PdTPTBP/PdTPNEt2P and perylene are combined with Cd0.5Zn0.5S for photocatalytic hydrogen production. These TTA-UC pairs convert visible light with the wavelength >510 nm that cannot be absorbed directly by Cd0.5Zn0.5S into blue light with smaller wavelength. Cd0.5Zn0.5S is then sensitized by this upconverted blue light to produce hydrogen. More importantly, the hydrogen production rate (8.44 mmol g-1h−1) of this integrated photocatalytic system is twice as high as that of the pure Cd0.5Zn0.5S microemulsion (4.04 mmol g-1h−1) under visible light (λ > 420 nm) irradiation, which is the best performance for the TTA-UC integrated photocatalytic system for hydrogen evolution ever reported so far. The high upconversion efficiency and high utilization efficiency of upconversion emission in microemulsion are responsible for the significantly promoted catalytic performance of this integrated photocatalytic system. The result demonstrates a simple strategy to integrate TTA-UC with photocatalyst for enhancing the hydrogen production efficiency. Considering the easily-tunable excitation/emission wavelength of TTA-UC pairs, this method could be used to integrate TTA-UC with a variety of photocatalysts.