This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: To produce hydrogen using sunlight, the energy obtained from light must be retained until it can be used in a chemical reaction. However, if an electron that has gained energy from light quickly returns to its original position, it becomes difficult to make use of that energy.
A KAIST-led research team has uncovered how tiny vacant sites inside a material that uses light to drive chemical reactions act like an "electron waiting room," providing more time for light energy to be utilized. The paper is published in the Journal of the American Chemical Society. The research team, led by Professor Tae Kyu Kim of the Department of Chemistry, in collaboration with research teams led by Professor Tae Wu Kim of Kyung Hee University, Professor Joonghan Kim of The Catholic University of Korea and Dr.
Jae Hyuk Lee of the Pohang Accelerator Laboratory, identified the mechanism by which "oxygen vacancies" in titanium dioxide help retain electrons for longer periods. Oxygen vacancies are empty sites created when oxygen atoms are missing from a material. Titanium dioxide is a representative photocatalytic material that promotes chemical reactions when exposed to light.
It has been studied in the fields of clean energy and environmental technology because it can be used to produce hydrogen using sunlight, convert carbon dioxide into useful substances and decompose pollutants. When light strikes this material, electrons gain energy and move, leaving behind "holes." Simply put, a hole is a site vacated by an electron. Electrons and holes can each participate in chemical reactions, but if an electron fills the hole again before taking part in a reaction, the opportunity to use the energy obtained from light is lost.
This process is called "recombination." Therefore, it is important to prevent electrons and holes from recombining too quickly and to secure enough time for them to participate in reactions. The research team focused on "blue titanium dioxide (blue TiO₂)," which has a bluish color due to the absence of some oxygen atoms. The oxygen vacancies in this material can serve as temporary sites where electrons remain.
While a hole is a "site vacated by an electron," an oxygen vacancy is a "site vacated by an oxygen atom," meaning the two are different. In this study, the researchers investigated how oxygen vacancies trap electrons and delay recombination. To do so, the team used the X-ray Free Electron Laser at the Pohang Accelerator Laboratory, a fourth-generation light-source facility.
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