Papers by Author: Morihiro Saito

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Authors: Katsuya Sakamoto, Hidenobu Shiroishi, Takaaki Shirai, Shunsuke Satou, Morihiro Saito, Jun Kuwano
Abstract: The ternary oxide compositions xZrO2-(0.5–x/2)Al2O3-yP2O5(x=0.8, 0.9, 0.95, 1.0; y=1.0, 1.2, 1.4) and 0.9ZrO2-0.05In2O3-1.4P2O5, xSiO2-(0.5–x/2)Al2O3-1.4P2O5(x=0.9, 1.0) were synthesized by sol-gel methods, and their conductivities were investigated by ac-impedance spectroscopy. The conductivity increased with increasing P2O5 content and with decreasing heat-treatment temperature. The maximum conductivities reached over 10-2 Scm-1 at 150°C for 0.9ZrO2-0.05Al2O3-1.4P2O5 and at 225°C for 0.9SiO2-0.05Al2O3-1.4P2O5.
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Authors: Naohisa Mori, Yutori Tagoku, Hidenobu Shiroishi, Yoshinobu Saito, Morihiro Saito, Jun Kuwano
Abstract: Photocatalytic proton reduction and water oxidation have been studied in a tris(2,2’-bipyridyl)ruthenium complex-catalyst system. Pyrochlore-type oxides have been used as proton reduction catalysts with a sacrificial electron donor (Na2EDTA) at pH 7 and as water oxidation catalysts with a sacrificial electron acceptor (K2S2O8) at pH 3. Rate constants for the proton reduction were estimated on the basis of photochemical processes. Yb2Ru2O7-δ was found to be the most active catalyst for proton reduction and water oxidation catalyst in this system.
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Authors: Masashi Hirakuri, Toyoki Okumura, Morihiro Saito, Jun Kuwano
Abstract: In order to reproduce the observed ionic conductivities and activation energies computationally, the potential parameters (PMs) were optimized for classical molecular dynamic simulations on Li ion conduction in the A-site deficient perovskite solid solution La056Li0.33TiO3 with disordered A-site ion arrangement. By the use of the optimized PMs, the conductivities and the activation energies were improved considerably from 4.1×10-3 Scm-1 to 4.4×10-2 Scm-1 at 800 K and 0.02 eV to 0.2 eV, respectively. The pair correlation functions calculated with the optimized PMs reveal that the Li-ions are located somewhat broadly mainly in the vicinity of the midpoint between the center of the A-site and the center of the bottleneck formed by four O2-, and that the simulated Li location is significantly related to the conductivity.
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Authors: Jun Kikuchi, Seiji Koga, Katsuyuki Kishi, Morihiro Saito, Jun Kuwano
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Authors: Toyoki Okumura, Ayumi Dodomi, Morihiro Saito, Jun Kuwano
Abstract: The locations and local environments of the Li ions in La0.56Li0.33TiO3 have been investigated by classical molecular dynamics (MD) simulations and first-principles (FP) calculations. The pair correlation functions of Li-O and Li-Ti indicate that the Li ions are located somewhat broadly mainly in the vicinity of the midpoint between the center of the A-site and the center of the bottleneck formed by four O2-. This is consistent well with that suggested from previous neutron diffraction and 6Li-NMR studies. The FP calculations suggest a different location of the Li ion in the vicinity of the midpoint between the centers of two adjcent bottlenecks; however it coincides with one of the locations shown by the trajectories simulated with the MD calculations.
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Authors: Kenji Yoshihara, Takeshi Chuma, Morihiro Saito, Jun Kuwano, Hidenobu Shiroishi
Abstract: The O2-gas electrode (OGE) properties of the pyrochlores Pb2Ru2-XMXO7-δ(M=Mn,Fe,Co,Ni) [PRMx] were examined below 300°C with the cell of the type (PRMx | Ba0.975Ce0.8Gd0.2O3 (BCG) | PRMx). The PRMn electrodes showed good OGE properties comparable to those of Pb2Ru2O6.5 and superior to those of a Pt-paste electrode and the La0.6Sr0.4Co0.98Ni0.02O3 electrode, which are well-known representative OGEs. The results indicate that the PRMn electrodes can be used for OGEs in low-temperature applications including oxygen sensors.
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Authors: Kenji Yoshihara, Yoshinobu Saito, Morihiro Saito, Jun Kuwano, Hidenobu Shiroishi
Abstract: The activities of the pyrochlores Pb2Ru2-xMxO7-δ (M=Mn,Fe,Co,Ni)[PRM(0x)] toward electrochemical oxygen reduction (EOR) were examined in 0.1 M KOH and 0.05 M H2SO4 aqueous solutions. The onset voltage (Vo) and the efficiency (E4) of 4-electron reduction of oxygen for PRM(0x) were evaluated by semi-steady state voltammetry with rotating ring-disk electrodes. In PRM01, the order of the EOR activities was PRMn01 > PRCo01 > PRNi01 > PRFe01 in both solutions. This was consistent with the variation of the lattice parameters, i.e. PRM01 with a smaller lattice parameter showed higher EOR activity. In addition, PRMn05 showed higher EOR activity than PRMn01. The onset voltages Vo were 0.95 and 0.50 V vs. reversible hydrogen electrode in 0.1 M KOH and 0.05 M H2SO4, respectively, while E4 was almost 100 % in both solutions. These results indicate that the EOR activity of PRM(0x) depends on the incorporated metal ions on the B-sites and their contents.
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Authors: Takayuki Konishi, Hideki Kawai, Morihiro Saito, Jun Kuwano, Hidenobu Shiroishi
Abstract: The trirutile oxides MTa2O6 (M=Co,Ni,Mg) [MTs] and the substitution products M1-xNxTa2-yLyO6 (N=Mn, L=Sn,Ti,Zr) [M1-xNxTa2-yLy] were prepared by a conventional solid-state reaction. The oxygen reduction reaction (ORR) activities were evaluated with the onset potentials (Eon) of the ORR currents, the disk current densities (iD) and the efficiencies (Eff4) of 4-electron reduction, measured by a rotating ring-disk electrode (RRDE) technique. All the samples showed ORR activities and the Eon values were around +0.8 V vs. RHE in 0.1 M KOH. The CoTa2O6 electrocatalyst showed the best ORR property of the MTs samples: its Eff4 value was as high as ~80%. With substitution of Ti or Sn, the ORR activities of MgTa1.9T0.1O6, CoTa1.8Sn0.2O6 and NiTa1.9Ti0.1O6 were improved in alkaline solution, compared with those of MTa2O6. In acid solution, the same substitution of Ti and Sn resulted in improvement of Eff4, but no significant improvements of Eon and iD.
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Authors: Kiyofumi Yamagiwa, Yuriko Iwao, Masafumi Mikami, Tsuneharu Takeuchi, Morihiro Saito, Jun Kuwano
Abstract: Vertically aligned carbon nanotubes (CNTs) were grown on a stainless steel substrate (SUS304) by resistance-heating method in alcohols containing homogeneously dissolved cobaltocene Co(C5H5)2 as a catalyst source. Straight-chain primary alcohols, 1,2-ethanediol and cyclohexanol were used as carbon sources to examine the effects of the molecular structures on the morphology of the aligned CNTs. Methanol brought the best purity and alignment of CNTs of all the alcohols. The CNTs from 1,2-ethanediol was worse in the purity than those from ethanol with the same number of carbon atoms. The CNTs from cyclohexanol had a better purity than those from 1-hexanol. Distinctive features of this method are simple, low cost and a one-step process involving none of vacuum processes and catalyst preparation processes.
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Authors: Yuya Akeboshi, Naotaka Ohno, Hirohito Tokuno, Morihiro Saito, Jun Kuwano, Hidenobu Shiroishi
Abstract: Two types of oxide nanosheet-based materials, a H3O+-exchanged layered titanate and restacked titania nanosheets (H3O+-RE) were synthesized by soft chemical methods, and their oxygen reduction reaction (ORR) activities were examined by semi-steady-state voltammetry with a rotating ring-disc electrode at 70°C in 0.05 M H2SO4. Both samples showed similar onset potentials of the ORR, ~ 0.50 vs. reversible hydrogen electrode, while the efficiencies (Eff4) of the 4-electron reduction of oxygen depended on their nanostructures, i.e. the stacking morphology of nanosheets, specific surface area and kinds of cation between the nanosheets. Both H3O+-form samples showed high Eff4 values are compared with Cs+-form layered titanate.and the H+-form restacked titania nanosheets. This reveals that the H3O+ions and the number of the active sites for ORR are related to the ORR activity. The H3O+-RE exhibited the best Eff4 value (> 90%), which is comparable to that of a conventional 20 mass% Pt/C catalyst.
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