Overlooked Compound Proves Useful For Photocatalysis

Oxyfluorides, once avoided due to the strong electronegativity of fluorine, have now been found to perform photocatalytic reactions in an exceptional case.

AsianScientist (Jun. 7, 2018) – Scientists in Japan have shown that an oxyfluoride is capable of visible light-driven photocatalysis, paving the way for new materials in artificial photosynthesis and solar energy research. They reported their findings in the Journal of the American Chemical Society.

Over the last decade, research has intensified to develop efficient, synthetic photocatalysts that work under visible light—an important target for renewable energy systems.

In the present study, scientists at the Tokyo Institute of Technology have developed a photocatalytic material called a pyrochlore oxyfluoride (Pb2Ti2O5.4F1.2). Led by Associate Professor Kazuhiko Maeda of Tokyo Institute of Technology (Tokyo Tech), the researchers demonstrated that Pb2Ti2O5.4F1.2 works as a stable photocatalyst for visible light-driven water splitting and carbon dioxide reduction.

The material had an unusually small band gap of around 2.4 electron volts (eV), meaning that it can absorb visible light with a wavelength of around 500 nanometers. In general, band gaps bigger than 3 eV are associated with inefficient utilization of sunlight, whereas those smaller than 3 eV are desirable for efficient solar energy conversion.

Additionally, the oxyfluoride belongs to a group of compounds that had until now been largely overlooked due to the high electronegativity of fluorine, a property that essentially ruled them out as candidates for visible light-driven photocatalysts. The new oxyfluoride is an exceptional case, the researchers say.

Based on structural considerations and theoretical calculations, they concluded that the origin of the visible light response in Pb2Ti2O5.4F1.2 lies in the the strong interaction between the Pb-6s and O-2p orbitals, enabled by short Pb-O bonding in the pyrochlore structure.

One limitation of the material is that its hydrogen yield remains low. The research team is therefore investigating how to boost the yield by modifying Pb2Ti2O5.4F1.2 through the refinement of methods for synthesis and surface modification.

The article can be found at: Kuriki et al. (2018) A Stable, Narrow-Gap Oxyfluoride Photocatalyst for Visible-Light Hydrogen Evolution and Carbon Dioxide Reduction.


Source: Tokyo Institute of Technology; Photo: Pexels.
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