AsianScientist (May 30, 2017) – In a study published in Angewandte Chemie, researchers in Japan describe a photocatalyst that increases the production of hydrogen tenfold. The discovery was made by a joint research team led by Associate Professor Takashi Tachikawa from Kobe University and Professor Tetsuro Majima of Osaka University.
When light is applied to photocatalysts, electrons and holes are produced on the surface of the catalyst, and hydrogen is obtained when these electrons reduce the hydrogen ions in water. However, in traditional photocatalysts the holes that are produced at the same time as the electrons mostly recombine on the surface of the catalyst and disappear, making it difficult to increase conversion efficiency.
Instead, Tachikawa’s research group developed a photocatalyst made of mesocrystal, a type of crystal that lacks the uniformity of regular crystals. This new photocatalyst is able to spatially separate the electrons and electron holes to prevent them recombining. As a result, it has a far more efficient conversion rate for producing hydrogen than conventional nanoparticulate photocatalysts.
By first using titanium oxide (TiO2), they were able to synthesize mesocrystal strontium titanate (SrTiO3) using a simple one-step hydrothermal reaction. By lengthening the reaction time, they could also grow larger particles near the surface while preserving their crystalline structure.
When they attached a co-catalyst to the synthesized mesocrystal and applied ultraviolet light in water, the reaction occurred with approximately seven percent light energy conversion efficiency. Under the same conditions, strontium titanate nanoparticles which had not been converted into mesocrystals reached a conversion efficiency of less than one percent, showing that the reaction efficiency increased tenfold under the mesocrystal structure.
When each particle was examined under a fluorescent microscope, the team found that the electrons in the newly-developed photocatalyst moved smoothly between the nanoparticles inside the mesocrystal, gathering around the larger nanocrystals generated on the surface of the crystal, and efficiently reducing the hydrogen ions to create hydrogen.
Using these findings, the research group plans to use mesocrystal technology to develop super-efficient hydrogen solar cells. As perovskite metal oxides such as strontium titanate are used in many electronics, these results could be applied to a wide range of fields, the researchers say.
The article can be found at: Zhang et al. (2017) Topotactic Epitaxy of SrTiO3 Mesocrystal Superstructures with Anisotropic Construction for Efficient Overall Water Splitting.
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Source: Kobe University.
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