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Hwang C.M.,University of Tsukuba | Ishida M.,University of Tsukuba | Ito H.,Japan National Institute of Advanced Industrial Science and Technology | Maeda T.,Japan National Institute of Advanced Industrial Science and Technology | And 6 more authors.
International Journal of Hydrogen Energy | Year: 2011

Polymer electrolyte-based unitized reversible fuel cells (URFCs) combine the functionality of a fuel cell and an electrolyzer in a single device. In a URFC, titanium (Ti)-felt is used as a gas diffusion layer (GDL) of the oxygen electrode, whereas typical carbon paper is used as a GDL of the hydrogen electrode. Different samples of Ti-felt with different structural properties (porosity and fiber diameter) and PTFE content were prepared for use as GDLs of the oxygen electrode, and the relation between the properties of the GDL and the fuel cell performance was examined for both fuel cell and electrolysis operation modes. Experimental results showed that the cell with a Ti-felt GDL of 80 μm fiber diameter had the highest round-trip efficiency due to excellent fuel cell operation under relatively high-humidity conditions despite degradation in performance in the electrolysis mode. © 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved. Source


Ito H.,Japan National Institute of Advanced Industrial Science and Technology | Maeda T.,Japan National Institute of Advanced Industrial Science and Technology | Nakano A.,Japan National Institute of Advanced Industrial Science and Technology | Hwang C.M.,University of Tsukuba | And 3 more authors.
International Journal of Hydrogen Energy | Year: 2012

Experimental study on proton exchange membrane (PEM) electrolyzer was carried out focusing on the effect of pore structural properties of current collectors, such as porosity and pore diameter. Various titanium (Ti)-felt substrates with different porosities and pore diameters (measured by capillary flow porometry) were used as the anode current collector. Results show that when the mean pore diameter of the current collector was larger than 10 μm, the electrolysis performance improved with decreasing pore diameter. In contrast, changes in porosity had no significant effect on the cell performance when the porosity exceeded 0.50. The flow pattern of two-phase flow in the flow channel was discussed in terms of its relationship to bubble size and to pore diameter of the current collector. Finally, correlation between the calculated membrane resistance and the measured pore diameter of the current collectors suggest that larger bubbles generated from larger pores tend to become long bubbles in the channel, thus hindering the water supply to the membrane. Copyright © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. Source


Okumura M.,Tohoku University | Terui K.,Tohoku University | Ikado A.,Tohoku University | Saito Y.,Tohoku University | And 5 more authors.
International Journal of Hydrogen Energy | Year: 2012

The strains generated in a reaction vessel of hydrogen storage alloys and the packing ratio distribution inside the vessel were measured in order to analyze the effects of packing on stress. More specifically strains generated on the vessel's surface were measured when hydrogen is repeatedly absorbed and desorbed by the packed bed in the reaction vessel. The amount of deformation, local packing ratios and relative particle volumes in the vessel were also measured after repeated hydrogen absorption-desorption. As absorption-desorption was performed repeatedly, agglomeration regions where the value of the local packing ratio was around 0.6 were formed, and particularly strong stress was generated in these regions, causing deformation. More hydrogen packing causes agglomeration regions to form over a wider area. Since alloys are pulverized by repeated absorption-desorption, and concentrate in the lower parts of the vessel, agglomeration regions are also formed in the lower parts. Our experiments also revealed that the resulting agglomeration regions have a packing ratio of about 0.6. Copyright © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights. Source


Tamura K.,Takasago Thermal Engineering Co.
Journal of Logic and Computation | Year: 2013

In this article, we prove that the hybrid μ-calculus, which is the modal μ-calculus extended with nominals and satisfaction operators in the language of hybrid logic, has the small model property as follows: every satisfiable formula is satisfied in a model whose size is bounded by some function on the size of the formula. The obtained bound on the size of the model is then used to obtain a finite, sound and complete axiomatization for this formal system. © 2013 © TheAuthor, 2013. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com. Source


Ito H.,Japan National Institute of Advanced Industrial Science and Technology | Maeda T.,Japan National Institute of Advanced Industrial Science and Technology | Nakano A.,Japan National Institute of Advanced Industrial Science and Technology | Kato A.,Takasago Thermal Engineering Co. | Yoshida T.,Daiki Ataka Engineering Co.
Electrochimica Acta | Year: 2013

The effect of pore structural properties (porosity and pore diameter) of current collectors in proton exchange membrane (PEM) electrolyzers on electrolysis performance was experimentally evaluated by using various titanium (Ti)-felt substrates with different porosities and pore diameters (measured by capillary flow porometry) as the anode current collectors. The current-potential (j-ΔV) characteristics were measured, and overpotential analysis was performed based on the j-ΔV characteristics and the cell resistance (Rcell) data. The results showed that (1) the effect of the decrease in water supply on the membrane resistance due to produced gas bubbles is limited when the mean pore diameter of the anode current collector is less than 50 μm, but might appear at the concentration overpotential, and (2) enhancing the uniform and sufficient contact between the current collector and the electrode reduces not only the contact resistance but also the activation overpotential. © 2012 Elsevier Ltd. Source

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