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Single Crystal ZrO2 Nanosheets Formed by Thermal Transformation for Solid Oxide Fuel Cells and Oxygen Sensors
journal contribution
posted on 2019-09-11, 19:06 authored by Tetsuya Yamada, Yuta Kubota, Yuki Makinose, Norihiro Suzuki, Kazuya Nakata, Chiaki Terashima, Nobuhiro Matsushita, Kiyoshi Okada, Akira Fujishima, Ken-ichi KatsumataMonoclinic ZrO2 with a
nanosheet structure has been
successfully synthesized via the thermal transformation of NH4Zr2F9 using a high-temperature ionothermal
synthesis. The samples were characterized by using X-ray diffraction,
field emission scanning electron microscopy, transmission electron
microscopy, atomic force microscopy, and conductivity measurements
with a multiprobe. The result indicates that the as-prepared samples
have a single crystal sheet structure with a thickness of 4 nm. To
the best of our knowledge, a thin film of single crystal monoclinic
ZrO2 has not been reported, even though ZrO2 is an important material. In the absence of the ionic liquid (butyl-2,3-dimethylimidazolium
tetrafluoroborate), the thermal transformation of NH4Zr2F9 produced porosity within the two-dimensional
structure, whereas in the presence of the ionic liquid, the homogeneous
sheet structure was maintained without porosity. The decomposition
temperature of the ionic liquid and transformation temperature of
NH4Zr2F9 were analyzed to investigate
the thermal transformation process; the thermal transformation was
completed before the combustion of the ionic liquid. The current vs
voltage curve of a ZrO2 nanosheet indicates high resistivity
and breakdown voltage (ca. 20 V), which are attributable to the single
crystal structure without grain boundaries. The ZrO2 is
utilized for solid oxide fuel cell and oxygen sensor; therefore, the
single crystal nanosheet with high resistivity is expected to be applied
to these fields. CeO2 single crystallized nanosheets were
also obtained by the proposed thermal transformation method in an
ionic liquid. The synthetic routes to obtain nanosheets are limited;
however, the proposed method has the potential to expand the number
of routes and enable the synthesis of nanosheet materials.