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Dive into the research topics where Sachio Okada is active.

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Featured researches published by Sachio Okada.


Journal of Fuel Cell Science and Technology | 2008

Ni-Fe Alloy-Supported Intermediate Temperature SOFCs Using LaGaO3 Electrolyte Film for Quick Startup

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

Effect of Dispersion of Nanosize Platinum Particles on Electrical Conduction Properties of Proton-Conducting Oxide SrZr0.9Y0.1O3 − α

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

Nanoionics phenomenon in proton-conducting oxide: Effect of dispersion of nanosize platinum particles on electrical conduction properties

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

Oxygen nonstoichiometry in SrCeO3-based high-temperature protonic conductors evaluated by raman spectroscopy

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

Defect chemistry and oxygen permeation property of Pr2Ni0.75Cu0.25O4 oxide doped with Ga

Tatsumi Ishihara; Kenichi Nakashima; Sachio Okada; Makiko Enoki; Hiroshige Matsumoto


Solid State Ionics | 2008

Intermediate-temperature solid oxide fuel cells using perovskite-type oxide based on barium cerate

Hiroshige Matsumoto; Ikuyo Nomura; Sachio Okada; Tatsumi Ishihara


Solid State Ionics | 2008

Introduction of In or Ga as second dopant to BaZr0.9Y0.1O3 − δ to achieve better sinterability

Naoki Ito; Hiroshige Matsumoto; Yuya Kawasaki; Sachio Okada; Tatsumi Ishihara


International Journal of Hydrogen Energy | 2009

Intermediate temperature steam electrolysis using strontium zirconate-based protonic conductors

Takaaki Sakai; Shotaro Matsushita; Hiroshige Matsumoto; Sachio Okada; Shin-ichi Hashimoto; Tatsumi Ishihara


Ionics | 2007

Hydrogen separation from syngas using high-temperature proton conductors

Hiroshige Matsumoto; Sachio Okada; Shin-ichi Hashimoto; Kazuya Sasaki; Reiri Yamamoto; Makiko Enoki; Tatsumi Ishihara


Solid State Ionics | 2004

Chemical stability of SrCe0.95Yb0.05O3−α in hydrogen atmosphere at elevated temperatures

Sachio Okada; Atsushi Mineshige; Akira Takasaki; Masafumi Kobune; Tetsuo Yazawa; Hiroshige Matsumoto; Tetsuo Shimura; Hiroyasu Iwahara; Zempachi Ogumi

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