Sachio Okada
Kyushu University
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Publication
Featured researches published by Sachio Okada.
Journal of Fuel Cell Science and Technology | 2008
Tatsumi Ishihara; Jingwang Yan; Makiko Enoki; Sachio Okada; Hiroshige Matsumoto
Intermediate temperature solid oxide fuel cells (SOFCs), which are highly tolerant against a thermal cycle, are studied by using the Ni-Fe porous alloy substrate prepared by an in situ reduction. It was found that Ni-Fe alloy exhibits high activity against anodic reaction and suitable compatibility with InGaO 3 electrolyte. The electrolyte film of La 0.9 Sr 0.1 Ga 0.8 Mg 0.2 O 3 (LSGM) and Sm 0.2 Ce 0.8 O 2 (SDC) bilayer with 5 μm thickness was successfully prepared on the dense NiO-Fe 2 O 3 composite anode. After a in situ reduction, the dense plate of NiO-Fe 2 O 3 was changed to the porous Ni-Fe alloy substrate; however, the LSGM film can keep the dense state. The prepared Ni-Fe alloy that supported LSGM cell demonstrated the maximum power densities of 0.9 W/cm 2 and 0.4 W/cm 2 at 873 K and 573 K. After heating up to 873 K within 540 s, there is no crack formed on the film and almost the theoretical open circuit voltage was exhibited. In addition, the maximum power density of 400 mW/cm 2 was achieved at 773 K. After the thermal cycling, the decrease in the maximum power density was not large, and this suggests that the film is still gas tight and highly tolerant against the thermal cycle. Quick start characteristics of the metal support SOFC could expand the SOFC application to the electric source of a mobile-field-like automobile.
Electrochemical and Solid State Letters | 2007
Hiroshige Matsumoto; Yoshihisa Furya; Sachio Okada; Takayoshi Tanji; Tatsumi Ishihara
Nanosize effects have gradually become emphasized in the description of ion conduction properties of solids. The authors demonstrate a nanoionics effect that occurs in a proton-conducting perovskite upon dispersing fine platinum particles in the oxide. Both the ionic and hole conductivities are lost when the volume fraction of dispersed platinum exceeds a threshold value, resulting in an enormous reduction in both conductivities. These experimental results are discussed in accordance with a percolation model: the boundary layer, where charge carriers are suppressed by a space charge layer effect, blocks the bulk conduction of both protonic and electron-hole charge carriers.
Science and Technology of Advanced Materials | 2007
Hiroshige Matsumoto; Yoshihisa Furuya; Sachio Okada; Takayoshi Tanji; Tatsumi Ishihara
Abstract High-temperature proton conductors are oxides in which low-valence cations are doped as electron acceptors; the incorporation of water molecules into the oxides results in the formation of protonic defects that act as charge carriers. Since the protons thus formed are in equilibrium with other electronic defects, electrons and holes, the oxides possibly have different proton-conduction properties at and near boundaries when they are in contact with another phase. In this paper, we present our recent experimental observation of a marked change in the electrical properties of a proton conductor upon the dispersal of fine platinum particles in the oxide. First, the material shows extremely low electrical conductivity in comparison with the original proton-conducting perovskite. Second, there was a threshold amount of platinum at which such a drop in conductivity occurred. A percolation model is employed to explain these experimental results; the fine platinum particles dispersed in the proton-conducting oxide wears highly resistive skin that is formed due to shifts in defect equilibriums, which prevents ionic/electronic conduction. The experiments suggest that the ion-conducting properties of oxides can be varied by introducing interfaces at a certain density; nanoionics is a key to yielding enhanced and/or controlled ionic conduction in solids.
Solid State Ionics | 2003
Atsushi Mineshige; Sachio Okada; Katsura Sakai; Masafumi Kobune; Satoshi Fujii; Hiroshige Matsumoto; Tetsuo Shimura; Hiroyasu Iwahara; Zempachi Ogumi
Abstract Raman spectra of Yb-doped strontium cerate SrCe 1−x Yb x O 3− δ were measured to evaluate their defect structure, which is much expected to influence their physical properties, such as solubility and diffusivity of protons in these oxides. In spectra, a signal showing existence of oxygen vacancies was observed at about 630 cm −1 for doped samples. The intensity of this band increased with oxygen vacancy formation by Yb-doping and by annealing at high temperatures in dry [low P (H 2 O)] or reducing [low P (O 2 )] conditions. Since a clear relationship between a peak intensity of the oxygen vacancy band and dopant concentration was obtained, it was found oxygen nonstoichiometry in SrCe 1− x Yb x O 3− δ system could be evaluated using this relationship.
Solid State Ionics | 2008
Tatsumi Ishihara; Kenichi Nakashima; Sachio Okada; Makiko Enoki; Hiroshige Matsumoto
Solid State Ionics | 2008
Hiroshige Matsumoto; Ikuyo Nomura; Sachio Okada; Tatsumi Ishihara
Solid State Ionics | 2008
Naoki Ito; Hiroshige Matsumoto; Yuya Kawasaki; Sachio Okada; Tatsumi Ishihara
International Journal of Hydrogen Energy | 2009
Takaaki Sakai; Shotaro Matsushita; Hiroshige Matsumoto; Sachio Okada; Shin-ichi Hashimoto; Tatsumi Ishihara
Ionics | 2007
Hiroshige Matsumoto; Sachio Okada; Shin-ichi Hashimoto; Kazuya Sasaki; Reiri Yamamoto; Makiko Enoki; Tatsumi Ishihara
Solid State Ionics | 2004
Sachio Okada; Atsushi Mineshige; Akira Takasaki; Masafumi Kobune; Tetsuo Yazawa; Hiroshige Matsumoto; Tetsuo Shimura; Hiroyasu Iwahara; Zempachi Ogumi