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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 | 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


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 3 more authors.
Journal of Power Sources | Year: 2012

Polymer electrolyte-based unitized reversible fuel cells (URFCs) can be operated either as an electrolyzer to split water into hydrogen and oxygen using electric power or as a fuel cell to supply electric power when fed hydrogen and oxygen or air. In a URFC, titanium (Ti)-felt is used as a gas diffusion layer (GDL) in the oxygen electrode and typical carbon paper is used as a GDL in the hydrogen electrode. Here, first, Ti-powder was loaded into the Ti-felt GDL in URFCs to produce an effective pore distribution for water management in the membrane. Then, the effect of this Ti-powder loading on the cell performance was examined for both fuel cell and electrolysis operations. Experimental results revealed that the Ti-powder loading significantly improved the fuel cell performance under fully humidified conditions (relative humidity (RH) = 100%), but not under relatively dry conditions (RH = 66%). In contrast, the Ti-powder loading had no effect on the electrolysis performance. © 2011 Elsevier B.V. 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 | Hasegawa Y.,Japan National Institute of Advanced Industrial Science and Technology | And 6 more authors.
International Journal of Hydrogen Energy | Year: 2010

The flow characteristics of circulating water in a proton exchange membrane (PEM) electrolyzer were experimentally evaluated using a small cell and two-phase flow theory. Results revealed that when a two-phase flow of circulating water at the anode is either slug or annular, then mass transport of the water for the anode reaction is degraded, and that the concentration overvoltage increases at higher current density compared to that when the flow is bubbly. In a serpentine-dual flow field, when both phases of the two-phase flow are assumed laminar, then the increase in pressure drop caused by the increase in gas production can be explained relatively well using the Lockhart-Martinelli method with the Chisholm parameter. The optimal flow rate of circulating water was also discussed based on mass balance analysis. © 2010 Published by Elsevier Ltd on behalf of Professor T. Nejat Veziroglu. Source


Ito H.,Japan National Institute of Advanced Industrial Science and Technology | Maeda T.,Japan National Institute of Advanced Industrial Science and Technology | Kato A.,Takasago Thermal Engineering Co. | Yoshida T.,Daiki Ataka Engineering Co. | Ulleberg O.,Institute for Energy Technology of Norway
Journal of the Electrochemical Society | Year: 2010

Unitized reversible fuel cells (URFCs) combine the functionality of a fuel cell (FC) and of an electrolyzer (Ely) in a single device. In polymer electrolyte URFCs, gas purging is crucial in switching from the Ely to the FC operation. A gas purge model was developed here to clarify the relationship between the purge time and the gas flow rate. The model considers evaporation and diffusion of liquid water in the gas diffusion layer and membrane. To validate our model, we compared model predictions of high frequency resistance vs purge time with experimental results for two URFCs of different sizes at different purge flow rates. The simulated curves agree well with the experimental curves. © 2010 The Electrochemical Society. Source

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