Unexpected Hydrogen Production of α-Fe2O3 Nanorings

The production of hydrogen from water using only a catalyst and solar energy, water photolysis, is one of the most challenging and promising outlets for the generation of clean and renewable energy. [1] Semiconductor photocatalysts for hydrogen production by water photolysis must employ stable, non-toxic, abundant and inexpensive visible-light absorbers capable of harvesting light photons with adequate potential to reduce water. Herein, we will present a-Fe₂O₃ nanorings (IONRs) and show that they can carry out hydrogen efficiently from water/methanol solution without applying any external bias. Our results indicate that IONRs could fill the requirements to split water due to a possible upward shift of the conduction band edge compared to bulk hematite [2], vary similar to that recently observed for CoO nanoparticles. [3] Understanding the underlying mechanisms for hydrogen evolution is currently being investigated in more details since the band gap, as measured by UV-Vis diffuse reflectance spectroscopy, is identical to bulk hematite removing the possibility of quantum confinement effect as observed elsewhere. [4] In addition, by depositing Co(OH)₂ nanoparticles (NPs) of ~ 6 nm diameter in the NRs with a H₂ evolution rate of 546 mmols.h^-1.g^-1 could be obtained, increasing by 35% the evolution of hydrogen. Both nanoparticle-coated and uncoated NRs displayed superior photocatalytic activity for hydrogen evolution when compared with P25-TiO₂nanoparticles, showing themselves to be promising materials for water-splitting using only solar light.

References

1. H. Wender et al, Nanoscale 5, 9310 (2013).
2. C. X. Kronawitter, et al, Energy Environ. Sci. 4, 3889 (2011).
3. Longb Liao, et al, Nature Nanotechnology 9, 69 (2014)
4. L. Vayssieres, et al, Adv. Mater. 17, 2320 (2005).