Visible-light sensitive hydrogen evolution photocatalyst ZnRh2O4

We investigated the ability of the oxide ZnRh2O4 to serve as a solar H-2-evolution photocatalyst due to the predicted potential of its conduction band bottom, which may allow thermodynamically favorable H-2 evolution in spite of its small band-gap of 1.2 eV. ZnRh2O4 produced H-2 in the presence of HCHO, but only scarcely in the presence of CH3OH, indicating that the potential of the valence band top of ZnRh2O4 lies at 0.1 V (vs. SHE). Thus, the conduction band bottom potential (similar to-1.1 V) lies much more negative than the potential of H+/H-2, allowing thermodynamically favorable H-2 evolution. In addition, the irradiated-light-wavelength dependence of the quantum efficiency (QE) for H-2 evolution was consistent with the solar spectrum, and the QE was quite high (similar to 27%), even at a wavelength of 770 +/- 25 nm. Taken together, our findings indicate that ZnRh2O4 can utilize solar light effectively, not only the entire range of UV and visible light, but is also sensitive to infrared light. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.