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Kim S.G.,Kongju National University | Kim J.-H.,The Fuel Team | Yim J.-H.,Kongju National University
Macromolecular Research | Year: 2013

The effects of graphite content, compression molding conditions, and types of catalysts on the mechanical and electrical properties and corrosion resistance of a graphite composite based on benzoxazine resin for the bipolar plate of polymer electrolyte membrane fuel cells (PEMFC) are provided in this study. Four kinds of catalysts based on imidazole (Im) acting as catalysts are investigated in order to enhance the physicochemical properties of the graphite/polybenzoxazine composites. The characteristics of the graphite composites based on benzoxazine resin with 85 wt% graphite content prepared via compression molding satisfy the US DOE targets for the bipolar plate of a PEMFC. A graphite composite based on polybenzoxazine with an Im-based catalyst having a relatively long alkyl chain shows the best performance in terms of flexural strength and corrosion resistance without sacrificing electrical conductivity. This graphite/polybenzoxazine composite can be successfully molded as a bipolar plate with excellent physicochemical properties through a compression molding process. © 2013 The Polymer Society of Korea and Springer Sciene+Business Media Dordrecht.

Yu H.N.,Korea Advanced Institute of Science and Technology | Kim S.S.,Korea Advanced Institute of Science and Technology | Suh J.D.,The Fuel Team | Lee D.G.,Korea Advanced Institute of Science and Technology
Composite Structures | Year: 2010

To fasten a fuel cell stack in a polymer electrolyte membrane fuel cell (PEMFC), two thick steel endplates have been used to maintain a proper contact pressure at the interfaces among gaskets, gas diffusion layer (GDL), membrane electrode assemblies (MEA), and bipolar plates. The proper contact pressure is required both to improve its energy efficiency by decreasing ohmic loss and to prevent leakage of fluid such as hydrogen, air, or coolant. Since the thick steel endplates are not only heavy, but also have high thermal conductivity and thermal inertia, which deteriorate the cold-start characteristics of fuel cell stack, a new development of the endplate with light weight and better thermal properties is necessary. In this work, to satisfy the two functional requirements, i.e. light weight and good cold-start characteristics, a sandwich construction composed of carbon fiber reinforced composite faces and a thermal insulation foam core was employed for the endplate. For the endplate design, the axiomatic design process and finite element analysis were used considering both structural and thermal characteristics of the endplate of a PEMFC. © 2009 Elsevier Ltd. All rights reserved.

Baik K.D.,Seoul National University | Hong B.K.,The Fuel Team | Kim M.S.,Seoul National University
International Journal of Hydrogen Energy | Year: 2013

In this study, the exact amount of oxygen crossover that reacts with hydrogen has been investigated using a mass spectrometer system. By measuring the amount of oxygen crossover that reacts with hydrogen, the exact amount of oxygen crossover that affects membrane degradation and/or water generation can be calculated under the fuel cell operating conditions. The amount of oxygen crossover that reacts with hydrogen is expressed as an effective oxygen crossover ratio, which is in a range between 0.927 and 0.933 under the fuel cell operating temperature conditions. This means that approximately 93% of the entire oxygen crossover through the membrane can affect membrane degradation and/or water generation at the anode catalyst layer. Thus, the effective oxygen crossover ratio should be considered as a novel index of oxygen crossover because it represents the exact amount of oxygen crossover that reacts with hydrogen. Copyright © 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

Baik K.D.,Seoul National University | Hong B.K.,The Fuel Team | Kim M.S.,Seoul National University
Renewable Energy | Year: 2013

This study examines the effects of operating parameters-comprising temperature, relative humidity, hydrogen pressure, and membrane thickness-on hydrogen crossover rate in a polymer electrolyte membrane fuel cell (PEMFC). It is found that the hydrogen crossover rate increases proportional to both temperature and relative humidity for all membrane samples. Increased hydrogen crossover rate is also observed with increasing hydrogen pressure. The hydrogen crossover rate increases gradually with the decrease of membrane thickness from 258 to 135 μm. When the membrane thickness decreases from 63 to 21 μm, there is a dramatic increase of hydrogen crossover. Multiple linear regression analysis was used to analyze the effects of all the operating parameters on hydrogen crossover rate. The results indicate that increased hydrogen crossover rate is mainly determined by the inverse of the logarithmic membrane thickness, followed by hydrogen pressure, relative humidity, and temperature, respectively. © 2013 Elsevier Ltd.

Jung C.-Y.,Hanyang University | Shim H.-S.,The Fuel Team | Koo S.-M.,Hanyang University | Lee S.-H.,Hanyang University | Yi S.-C.,Hanyang University
Applied Energy | Year: 2012

A two-dimensional, non-isothermal model of a proton exchange membrane fuel cell was implemented to elucidate heat balance through the membrane electrode assembly (MEA). To take local utilization of platinum catalyst into account, the model was presented by considering the formation of agglomerated catalyst structure in the electrodes. To estimate energy balance through the MEA, various modes of heat generation and depletion by reversible/irreversible heat release, ohmic heating and phase change of water were included in the present model. In addition, dual-pathway kinetics, that is a combination of Heyrovsky-Volmer and Tafel-Volmer kinetics, were employed to precisely describe the hydrogen oxidation reaction. The proposed model was validated with experimental cell polarization, resulting in excellent fit. The temperature distribution inside the MEA was analyzed by the model. Consequently, a thorough investigation was made of the relation between membrane thickness and the temperature distribution inside the MEA. © 2011 Elsevier Ltd.

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