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Fujii K.,JX Nippon Oil and Energy Co. | Sato Y.,JX Nippon Oil and Energy Co. | Takase S.,Kyushu Institute of Technology | Shimizu Y.,Kyushu Institute of Technology
Journal of the Electrochemical Society | Year: 2014

A series of pyrochlore-type lead-ruthenium oxide (Pb2Ru2O7-δ) containing various amounts of oxygen vacancies was prepared by varying the heat-treatment temperature, and the oxygen reduction reaction (ORR) activity as well as the electrochemical redox property in acid and alkaline solution was evaluated using rotating disk electrode. The specific ORR activity was increased with increasing the amount of oxygen vacancies, and linearly correlated to the charge amount of electrochemical redox of Pb2Ru2O7-δ both in acid and alkaline solution. We concluded that the surface oxygen vacancy participates in the electrochemical redox of Pb2Ru2O7-δ, and at the same time, behaves as the active site for ORR. The ORR activity in alkaline solution was much higher than that in acid solution, possibly because of the difference of the facility of electrochemical desorption of adsorbed oxygen species in the ORR process. Additionally, the effect of humidity on the ORR activity was investigated by single cell test. It was revealed that Pb2Ru2O7-δ shows absolutely high ORR activity in dry condition. © The Author(s) 2014.

Nakagami Y.,Osaka University | Nakagami Y.,JX Nippon Oil and Energy Co. | Kimizuka H.,Osaka University | Ogata S.,Osaka University | Ogata S.,Kyoto University
Nippon Kinzoku Gakkaishi/Journal of the Japan Institute of Metals | Year: 2016

Nanosized precipitates of solute atoms, which are often called "Guinier-Preston (GP) zones," are known to play a significant role in the precipitation-hardening effect on the Al alloys. In this study, the controlling factors for the formation of solute nanoclusters as in GP1 and GP2 zones, which are observed in the early and middle stages, respectively, of aging in the Al-Cu system, were investigated by extracting and examining the intra-and intercluster interaction energies of Cu in Al using density functional theory (DFT). DFT-calculated two-and three-body binding energies for Cu indicated that a Cu-Cu pair tends to bind at the first nearest-neighbor (1NN) positions, and a Cu-Cu-Cu triplet energetically prefers the arrangement of the triangular atomic cluster that contains two Cu-Cu pairs at the 1NN positions on the same {100} plane. Such a characteristic short-range ordering was suggested to be dominated by attractive three-body interactions due to the chemical (charge localization) effect, leading to planar clustering as found in the GP1 zones along the {100} planes. Intercluster interaction energies between two Cu planar clusters in Al were also calculated based on DFT. The results indicated that the energetically preferable configuration was the one in which two planar clusters are aligned at an intercluster distance of 2a (where a is the lattice constant of Al); it is noteworthy that this distance was the same to that in the basic structures of the GP2 zones observed in the experiments. A potential model for a dilute Al-Cu system was constructed on the basis of the extracted intra-and intercluster interactions, and then applied to atomistic Monte Carlo modeling for predicting the planar segregation of Cu atoms at finite temperatures. As a result, the formation of planar Cu clusters and the alignment of two planer clusters separated by 2a were successfully reproduced within a specific temperature range. This demonstrated that these interactions were important controlling factors for the formation of a characteristic pattern of solute clusters in the Al-Cu system. © 2016 The Japan Institute of Metals and Materials.

Fujii K.,JX Nippon Oil and Energy Co. | Ito M.,JX Nippon Oil and Energy Co. | Sato Y.,JX Nippon Oil and Energy Co. | Takenaka S.,Kyushu University | Kishida M.,Kyushu University
Journal of Power Sources | Year: 2014

Pd metal particles supported on a high surface area carbon black (Pd/CB) were covered with silica layers to improve the durability under severe cathode condition of proton exchange membrane fuel cells (PEMFCs). The performance and the durability of the silica-coated Pd/CB (SiO2/Pd/CB) were investigated by rotating disk electrode (RDE) in aqueous HClO4 and single cell test of the membrane-electrode assemblies (MEAs). SiO2/Pd/CB showed excellent durability exceeding Pt/CB during potential cycle in single cell test as well as in RDE measurement while Pd/CB significantly degraded. Furthermore, the MEA using SiO2/Pd/CB as the cathode catalyst showed higher performance than that using Pd/CB even in the initial state. The catalytic activity of SiO2/Pd/CB was higher than that of Pd/CB, and the drop of the cell performances due to the inhibition of electron conduction, proton conduction, and oxygen diffusion by the silica layer was not significant. It has been shown that the silica-coating is a very practical technique that can stabilize metal species originally unstable in the cathode condition of PEMFCs without a decrease in the cell performance. © 2015 Elsevier B.V. All rights reserved.

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