Papers - OKUYAMA Yuji
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Leonard K., Okuyama Y., Takamura Y., Lee Y., Miyazaki K., Ivanova M., Meulenberg W., Matsumoto H.
Journal of Materials Chemistry A 6 ( 39 ) 19113 - 19124 2018.1
Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Materials Chemistry A
© 2018 The Royal Society of Chemistry. Ceramic proton conductors have the potential to become important components in future clean and efficient energy technologies. In this manuscript, barium cerium yttrium zirconate (Ba(Zr0.5Ce0.4)8/9Y0.2O2.9) and strontium cerium yttrium zirconate (SrZr0.5Ce0.4Y0.1O2.95), proton conducting perovskites were employed as solid oxide electrolysis cell (SOEC) electrolytes for hydrogen production via intermediate temperature steam electrolysis at 550 and 600 °C. Cathode-supported button cells examined for a 12 μm Ba(Zr0.5Ce0.4)8/9Y0.2O2.9electrolyte, with Ni-SrZr0.5Ce0.4Y0.1O2.95as the H2-electrode, and porous Ba0.5La0.5CoO3as the anode reached current densities of 0.2 and 0.5 A cm-2with applied voltage of 1.45 V, at 550 and 600 °C, respectively. Moreover, a hydrogen evolution rate of 127 μmol cm-2per minute was achieved at 0.5 A cm-2, translating to a current efficiency of 82%. In addition, excellent cell performance was obtained using SrZr0.5Ce0.4Y0.1O2.95as an electrolyte. Current densities of 0.2 and 0.5 A cm-2were obtained at 600 °C with applied voltages of 1.28 and 1.63 V, achieving faradaic current efficiencies of 88 and 85%. The NiO-SrZr0.5Ce0.4Y0.1O3-δcomposite cathode was more favorable for the densification of the supported Ba(Zr0.5Ce0.4)8/9Y0.2O2.9electrolyte during sintering and could be promising for use as a cathode substrate in proton-conducting SOECs.
DOI： 10.1039/c8ta04019b
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Okuyama Y., Ymaguchi T., Matsunaga N., Sakai G.
Materials Transactions 59 ( 1 ) 14 - 18 2018
Language：English Publishing type：Research paper (scientific journal) Publisher：Materials Transactions
© 2017 The Japan Institute of Metals and Materials. In order to clarify the effect of the dopant concentration and phase transition on the proton conduction and proton concentration, the electrical conductivity and proton concentration were determined for La 1-x Ba x Yb 0.5 In 0.5 O 3-d (x = 0.1. 0.3. 0.5, 0.7). The phase transition from the orthorhombic system to the cubic system was over x = 0.3. The proton/deuteron isotope effect on the conductivity was observed for all samples at 673 K. The proton concentration was independent of the barium content above 673 K. The proton concentration increased with the barium content below 673 K, but the concentration ratio of the proton to dopant decreased following an increase in the barium concentration. It was determined that the dopant concentration and phase transition do not have an in uence on the conduction and incorporation of protons into the La 1-x B ax Yb 0.5 In 0.5 O 3-d .
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A direct methane fuel cell with double-layered electrolyte using proton conducting oxide Reviewed
Okuyama Y., Kawano S., Sakai G., Matsunaga N., Mizutani Y.
ECS Transactions 78 ( 1 ) 1953 - 1961 2017.5
Language：English Publishing type：Research paper (international conference proceedings) Publisher：ECS Transactions
© The Electrochemical Society. BaCe 0.8 Y 0.2 O 3-δ (BCY) has high proton conductivity, but is less stable against carbon dioxide. La 0.9 Sr 0.1 Yb 0.8 In 0.2 O 3-δ (LSYbIn) is chemically stable, but not as conductive as BCY. In this study, the performance of a methane fuel cell using BCY and LSYbIn as electrolytes was evaluated. The fuel cell using BCY showed shortterm degradation. On the other hand, the fuel cell using LSYbIn showed high durability using methane. The protonic ceramic fuel cell with a double-layered electrolyte was developed to improve chemical stability toward methane and the fuel cell performance. LSYbIn was used as the fuel side intermediate layer of the fuel cell using BCY for protection from methane. The fuel cell with a double-layered electrolyte suppressed the degradation by methane.
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Leonard K., Lee Y., Okuyama Y., Miyazaki K., Matsumoto H., Matsumoto H.
International Journal of Hydrogen Energy 42 ( 7 ) 3926 - 3937 2017.2
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：International Journal of Hydrogen Energy
© 2016 Hydrogen Energy Publications LLCDense yttrium doped solid solutions of alkaline earth cerate and zirconate with the formula A(Zr5/9Ce4/9)1−xYxO3−δ, (A = Sr and Ba, x = 0.1, 0.2) have been prepared and studied as potential proton conducting electrolytes. Thermo-gravimetric analysis was used to determine the proton concentration in the specimens. BZCY(54)8/92 showed a maximum proton concentration limit of 17.1 mol % compared to only 6.03 mol % for SZCY(54)8/92 and retained the highest proton conductivity of 1.44 × 10−2 S cm−1 in wet 1% H2 at 600 °C. Sufficient chemical stability under 80% steam for 200 h was confirm for the said composition. Approximately similar proton mobility levels were observed at 600 °C for the compositions. The major difference in total conductivity originates mostly from the differences in proton concentration levels. The bulk and grain boundary contributions on the conductivity were strongly dependent on the A-site host, with the grain boundary response being the main source of resistance in the BZCY specimens relative to the SZCY.
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Obukuro Y., Ninomiya K., Arai M., Okuyama Y., Sakai G., Matsushima S.
Computational Materials Science 126 7 - 11 2017.1
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Computational Materials Science
© 2016 Elsevier B.V.The electronic structure of LaYbO3 was investigated by the full potential linearized augmented plane wave plus local orbital (FLAPW + lo) method with the modified Becke–Johnson potential combined with the local density approximation correlation plus onsite Coulomb interaction (MBJ–LDA + U) for the sake of localized f electrons. This approach was suitable for evaluating electronic structure of LaYbO3 system from view point of calculation cost and time. The band gap, the difference in energy between the valence band (VB) and conduction band (CB), was estimated to be 6.0 eV by the present method. The evaluated value was very close to the reported experimental value. In the VB, Yb 4f orbitals and O 2p orbitals were well hybridized each other to state predominantly. The lower potential region in CB was mainly composed of La 4f orbitals, while the upper region in CB was mainly consisted of La 5d orbitals.
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固体電解質センサによるディーゼル排気ガス中の水素濃度測定 Reviewed
常吉孝治、高橋総子、岩井翔、奥山勇治
自動車技術会論文 48 ( 6 ) 1171 - 1175 2017
Language：Japanese Publishing type：Research paper (conference, symposium, etc.)
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Hydrogen Concentration Measuring by Proton Conductor Ceramics with Heater
TSUNEYOSHI Koji, TAKAHASHI Fusako, IWAI Tsubasa, OKUYAMA Yuji
The Proceedings of Conference of Tokai Branch 2017 ( 0 ) 2017
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Mechanical Engineers
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Obukuro Y., Matsushima S., Obata K., Suzuki T., Arai M., Asato E., Okuyama Y., Matsunaga N., Sakai G.
Journal of Alloys and Compounds 658 139 - 146 2016.2
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Journal of Alloys and Compounds
© 2015 Elsevier B.V.Single-phase Sr2Bi2O5 was obtained by calcination of the heterobimetallic complex precursor Sr[Bi(DTPA)]·9H2O (DTPA is diethylenetriaminepentaacetic acid) at 700 °C for 6 h. The effect of La doping on the crystal structure, surface area, morphology, surface chemical state, and absorption properties of Sr2Bi2O5 samples prepared from Sr[Bi(DTPA)]·9H2O were investigated. No traces of an impurity phase were detected in samples with a lower La content (3 and 5 mol%), while impurity phases such as Sr6Bi2O9 and SrCO3 were observed in Sr2Bi2O5 samples with larger La contents of 8 and 10 mol%. The Brunauer-Emmett-Teller surface area of Sr2Bi2O5 increased slightly with the content of La. High-resolution transmission electron microscopy revealed clear crystalline planes for both undoped and La-doped Sr2Bi2O5 samples without amorphous phases. Meanwhile, X-ray photoelectron spectroscopy indicated that the valence states of constituent metals were Sr2+, Bi3+, and La3+. The solubility limit of La in the Sr2Bi2O5 crystal phase was determined from Raman scattering measurements. La atoms substituted Bi sites when the doping content was low, while both Bi and Sr sites were substituted with La when the content of La was high. The electronic structure of Sr2Bi2O5 could be modified by La doping, resulting in a red shift of the absorption edge with increasing La content. The band-gap narrowing of Sr2Bi2O5 with La-doping was reproduced in energy-band calculations. The photocatalytic activity of Sr2Bi2O5 under visible-light irradiation for the oxidation of isopropanol was enhanced by doping with La.
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Sakai G., Tanaka A., Sueda T., Ogata T., Okuyama Y., Matsunaga N.
Chemistry Letters 45 ( 3 ) 318 - 320 2016
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Chemistry Letters
© 2016 The Chemical Society of Japan.Crystal growth under hydrothermal treatment at 150 °C was observed for the pre-calcined TiO2-SnO2 precursor obtained by the calcination at 250 °C. This phenomenon was observed for the trivalent titanium ion (Ti3+) used as the starting material for hydrolysis. The peculiar crystal growth phenomenon was thought to be originated from the oxidation of titanium from trivalent to tetravalent, because such peculiar crystal growth under hydrothermal conditions was not observed when tetravalent titanium was used.
DOI： 10.1246/cl.151106
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Okuyama Y., Nagamine S., Nakajima A., Sakai G., Matsunaga N., Takahashi F., Kimata K., Oshima T., Tsuneyoshi K.
RSC Advances 6 ( 40 ) 34019 - 34026 2016
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：RSC Advances
© The Royal Society of Chemistry 2016.In order to simplify the structure of the EMF-type hydrogen sensor using a proton conductor as the electrolyte, an electrolyte serving as a self-standard electrode in air was developed. The electrochemical properties and proton dissolution mechanism of Mn-doped CaZrO3 were evaluated by impedance analysis, EMF measurement, IR absorption analysis and ESR measurement. Mn-doped CaZrO3 acquires a proton from hydrogen by reduction of the manganese ion. 5 mol% Mn doped CaZrO3 showed proton conduction in a reducing atmosphere and hole conduction in an oxidizing atmosphere. A gas concentration cell using CaZr0.95Mn0.05O3-δ as the electrolyte was constructed for use as a hydrogen sensor. It was found to be dependent only on the hydrogen potential of the working electrode when air was used as the reference gas.
DOI： 10.1039/c5ra23560j
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Okuyama Y., Isa K., Lee Y., Sakai T., Matsumoto H., Matsumoto H.
Solid State Ionics 275 35 - 38 2015.7
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Solid State Ionics
© 2015 Elsevier B.V. All rights reserved.In order to clarify the mixed effect of a cation on proton conduction, the electrical conductivity and the proton concentration of SrCe0.9 - xZrxY0.1O3 - δ (x = 0.0, 0.3, 0.5, 0.7, 0.9) were measured by the AC impedance method and thermogravimetric analysis at 573-1173 K. The electrical conductivity reached a maximum value at x = 0.5. The proton concentration at x = 0.5 is the highest at this experimental temperature. The condition of the oxygen vacancy was examined by a Raman spectroscopic analysis. The Raman band around 350 cm- 1 attributed to the CeO6 stretching mode was observed and the half band width of the peak is broad when the cation on the B site is a mixture of Ce4 + and Zr4 +. It was found that the symmetry of the octahedron around B-site might be reduced due to the cation mix on the B-site.
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Improvement of protonic ceramic fuel cells with thin film BCZY electrolyte
Okuyama Y., Ebihara N., Okuyama K., Mizutani Y.
ECS Transactions 68 ( 1 ) 2545 - 2553 2015
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：ECS Transactions
© The Electrochemical Society.The performance of protonic ceramic fuel cells (PCFCs) using thin film BaCe<inf>0.6</inf>Zr<inf>0.2</inf>Y<inf>0.2</inf>O<inf>3-δ</inf> (BCZY622) electrolyte has been studied. The reference cell with the La<inf>0.8</inf>Sr<inf>0.2</inf>MnO<inf>3-δ</inf> cathode and Ni anode showed poor performance and short-term degradation. The overpotential of the anode and ohmic loss were the major factors for degradation, and a solid solution of Ni in the BCZY electrolyte has been observed. The electrical conductivity and the proton concentration of BCZY and BCZY622 doped with 5wt% NiO were measured by an impedance analysis and thermogravimetric analysis. The electrical conductivity and the proton concentration of BCZY622 decreased by introducing NiO. To avoid short-term degradation, the cell construction, manufacturing process, and cathode materials were improved. As a result, a carefully designed PCFC with thin film BCZY622, Ba<inf>0.5</inf>Sr<inf>0.5</inf>Co<inf>0.8</inf>Fe<inf>0.2</inf>O<inf>3-δ</inf> cathode and Ni/BCZY622 cermet anode showed good power density of 200-300mW/cm<sup>2</sup> in the wide temperature range of 873-1073K, and had stable power generation.
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Formation of CaFe<sub>2</sub>O<sub>4</sub> porous structure by addition of Zr in malic acid complex
OBUKURO Yuki, OBATA Kenji, MAEDA Ryosuke, MATSUSHIMA Shigenori, OKUYAMA Yuji, MATSUNAGA Naoki, SAKAI Go
Journal of the Ceramic Society of Japan 123 ( 1442 ) 995 - 998 2015
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Ceramic Society of Japan
The effect of Zr addition into malic acid complex was examined for the purpose of the improvement of microstructure and specific surface area of CaFe<sub>2</sub>O<sub>4</sub>. The CaFe<sub>2</sub>O<sub>4</sub> phase could be obtained for both unadded and Zr-added (5 and 10 mol % with respect to Fe) system by calcination of precursor derived from malic acid complex at 700°C which is almost 200°C lower than that of conventional solid-state reaction method. Among the examined products, only the 5 mol % Zr-added product revealed characteristic smaller grains connected three dimensional porous structures resulting in higher specific surface area compared with unadded and 10 mol % Zr-added products. XPS measurements revealed that there are no notable changes in valence state for all constituent elements. The obtained final product of 5 mol % Zr-added CaFe<sub>2</sub>O<sub>4</sub> is worth further investigate for various application from a view point of improved higher specific surface area and characteristic microstructure as well as the functionality of the material itself.
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Obukuro Yuki, Sakai Go, Okuyama Yuji, Matsunaga Naoki, Matsushima Shigenori, Obata Kenji, Asato Eiji
Chemistry Letters 44 ( 7 ) 890 - 892 2015
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Chemical Society of Japan
Single-phase Sr<sub>2</sub>Bi<sub>2</sub>O<sub>5</sub> was formed by calcination of the heterobimetallic complex, Sr[Bi(DTPA)]·9H<sub>2</sub>O, at 700 °C for 6 h in air. La-doping by 5 and 10 mol % into Sr<sub>2</sub>Bi<sub>2</sub>O<sub>5</sub> was also examined. There were no traces of impurity phase in the 5 mol % La-doped Sr<sub>2</sub>Bi<sub>2</sub>O<sub>5</sub> powder, on the other hand, impurity phases such as Sr<sub>3</sub>Bi<sub>4</sub>O<sub>9</sub> and SrCO<sub>3</sub> were identified for the 10 mol % La-doped sample. UV–vis spectroscopy revealed that the absorption edge of La-doped Sr<sub>2</sub>Bi<sub>2</sub>O<sub>5</sub> exhibits red shift as compared to the pure Sr<sub>2</sub>Bi<sub>2</sub>O<sub>5</sub> and the shift increases with the increase of La<sup>3+</sup> doping. It was confirmed that the photocatalytic activity of Sr<sub>2</sub>Bi<sub>2</sub>O<sub>5</sub> for the oxidation of isopropanol is improved with La doping under visible-light irradiation (λ ≥ 420 nm).
DOI： 10.1246/cl.150178
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Okuyama Y., Okuyama Y., Okuyama K., Mizutani Y., Sakai T., Lee Y., Matsumoto H., Matsumoto H., Matsumoto H.
International Journal of Hydrogen Energy 39 ( 35 ) 20829 - 20836 2014.12
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：International Journal of Hydrogen Energy
© 2014 Hydrogen Energy Publications, LLC. All rights reserved.The electrochemical properties of La0.9Sr0.1Yb0.8In0.2O3-δ (LSYbIn) were investigated by impedance measurements and the fuel cell performance test. The dominant charge carrier is the proton at low temperature. The hole is the dominant charge carrier in an oxidizing atmosphere at high temperature. Based on the conductivity data, the hydrogen potential profile and steady state current in the fuel cell at the polarized state were evaluated by calculation. The performance of the PCFC (protonic ceramic fuel cell) using LSYbIn as the electrolyte was examined in the temperature range of 873-1073 K. The maximum power density was 8.2 mW cm-2 at 1073 K.
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Okuyama Y., Ikeda S., Sakai T., Matsumoto H.
Solid State Ionics 262 865 - 869 2014.9
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Solid State Ionics
In order to clarify the mixing effect of cation on the electrical conductivity and the hydration, the electrical conductivity of La 0.9 Sr 0.1 (Yb 1 - x M x )O 3 - δ (M = In, Y) has been determined by the four-probe AC technique in the temperature range of 673-1173 K. The proton concentration was estimated from the change in weight due to hydration by a thermogravimetric analysis. The conductivity and proton concentration increased with the increase in the In 3 + content on the Yb-site. On the other hand, the electrical conductivity and protonic concentration of La 0.9 Sr 0.1 (Yb 1 - x Y x )O 3 - δ showed minimum values at x = 0.5. © 2013 Elsevier B.V. All rights reserved.
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Preparation of nano-structured cathode for protonic ceramic fuel cell by bead-milling method
Oda H., Yoneda T., Sakai T., Okuyama Y., Matsumoto H.
Solid State Ionics 262 388 - 391 2014.9
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Solid State Ionics
We developed a nano-structured Sm 0.5 Sr 0.5 CoO 3 (SSC55) cathode from slurry dispersed nanoparticles using a planetary bead-milling method. In order to evaluate the cathode performance, the cathode resistances and the protonic ceramic fuel cell properties were examined using electrochemical cells with a BaCe 0.6 Zr 0.2 Y 0.2 O 3 - δ electrolyte disk at intermediate temperatures. The cells with a milled SSC55 cathode showed lower cathode resistance and higher power density compared to those with the SSC55 cathode prepared from the conventional method. The improvement is attributed to an increase in the cathode reaction sites caused by the use of the smaller particles and a good adhesion to the electrolyte surface. © 2013 Published by Elsevier B.V.
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Development of electromotive-force type hydrogen sensor for copper melting process
53 ( 1 ) 171 - 176 2014.8
Language：Japanese Publishing type：Research paper (scientific journal)
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Incorporation and conduction of proton in Sr-doped LaMO<inf>3</inf>(M=Al, Sc, In, Yb, Y)
Okuyama Y., Kozai T., Ikeda S., Matsuka M., Sakai T., Matsumoto H.
Electrochimica Acta 125 443 - 449 2014.4
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Electrochimica Acta
In order to clarify the effect of the B site species in ABO 3 perovskite oxides on the proton transport properties, the proton incorporation into a series of La 0.9 Sr 0.1 MO 3-δ , (M = Al, Sc, In, Yb, Y) was studied by measuring the electrical conductivity and electromotive forces of the gas concentration cells, and by a thermogravimetric analysis. The proton concentration and electrical conductivity increased in the order of the B site species, Al < Y=Yb < Sc < In and Al < Y=Yb < In < Sc, respectively. La 0.9 Sr 0.1 AlO 3-δ showed an oxide ion conductivity, while La 0.9 Sr 0.1 YbO 3-δ and La 0.9 Sr 0.1 YO 3-δ exhibited a protonic conductivity in the temperature range of 573-1173 K. La 0.9 Sr 0.1 ScO 3-δ and La 0.9 Sr 0.1 InO 3-δ showed a protonic conductivity under 873 K, and a mixed proton and oxide ion conductivity at 1073 K. © 2014 Elsevier Ltd.
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Oda H., Okuyama Y., Sakai T., Matsumoto H.
Materials Transactions 55 ( 4 ) 722 - 727 2014
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Materials Transactions
Nano-structured La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-∞ (LSCF6428) cathode for protonic ceramic fuel cell (PCFC) prepared from planetary bead-milled nanoparticles was investigated. The cathode made by the bead-milled particles showed a porous structure consisting of homogeneous size particles and pores in the range 100 nm. The PCFC comprised of this cathode, Ni anode and BaCe 0.6 Zr 0.2 Y 0.2 O 3-∞ (BCZY622) electrolyte increased the cell performances about 6 times that of the cell using the cathode without milling. The cathode preparation using bead-milling is effective in improving the cell performance with an expanded contact area of the cathode/electrolyte interface due to decreasing particle size and good adhesion of the particles to the electrolyte. © 2014 The Japan Institute of Metals and Materials.