Electrochemical Crystal Growth of Titanium Oxyfluorides-A Strategy for Development of Electron-Doped Materials

Yusuke Chiba; Kengo Shibata; Hiroshi Takatsu; Kotaro Fujii; Miwa Saito; Hiroshi Kageyama; Kazuhiko Maeda; Masatomo Yashima; Teruki Motohashi

doi:10.1021/acs.inorgchem.1c01640

Electrochemical Crystal Growth of Titanium Oxyfluorides-A Strategy for Development of Electron-Doped Materials

Inorg Chem. 2021 Oct 4;60(19):14613-14621. doi: 10.1021/acs.inorgchem.1c01640. Epub 2021 Aug 31.

Authors

Yusuke Chiba^{1

2}, Kengo Shibata³, Hiroshi Takatsu⁴, Kotaro Fujii³, Miwa Saito¹, Hiroshi Kageyama⁴, Kazuhiko Maeda³, Masatomo Yashima³, Teruki Motohashi¹

Affiliations

¹ Department of Materials and Life Chemistry, Faculty of Engineering, Kanagawa University, Yokohama, Kanagawa 221-8686, Japan.
² Japan Society for the Promotion of Science (JSPS), Kojimachi Business Center Building, 5-3-1 Kojimachi, Chiyoda-ku, Tokyo 102-0083, Japan.
³ Department of Chemistry, School of Science, Tokyo Institute of Technology, 2-12-1-NE-2 Ookayama, Meguro-ku, Tokyo 152-8551, Japan.
⁴ Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan.

PMID: 34463090
DOI: 10.1021/acs.inorgchem.1c01640

Abstract

We report on the growth of single crystals of an electron-doped titanium oxyfluoride, Li₂Ti(O,F)₃, employing high-temperature electrolysis of TiO₂ with a eutectic Li₂MoO₄-LiF melt. Greenish octahedral-shaped crystals (∼30 μm in size) with a cubic rocksalt-type structure were successfully obtained by precisely tuning the applied voltage. The temperature-dependent magnetic susceptibility data revealed a paramagnetic behavior at low temperatures, ensuring the presence of Ti³⁺ ions (mean valence number of +3.78; F/Ti ∼ 0.15). The crystals exhibited clear visible-light absorption and produced H₂ from water in the presence of a sacrificial reagent under UV-light irradiation. Li₂Ti(O,F)₃ more efficiently produced H₂ compared with a nondoped oxyfluoride Li₅Ti₂O₆F, likely due to the doped electrons for the former. This work highlights a promising electrochemical approach toward growing electron-doped oxyfluoride crystals.