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Yoon S.,The Fuel Team | Bae J.,KAIST | Lee S.,KAIST | Pham T.V.,Saudi Aramco | Katikaneni S.P.,Saudi Aramco
International Journal of Hydrogen Energy | Year: 2012

Post-reforming experimental results for the complete removal of light hydrocarbons from diesel reformate are introduced in part I. In part II of the paper, an integrated diesel fuel processor is investigated for the stable operation of SOFCs. Several post-reforming processors have been operated to suppress both sulfur poisoning and carbon deposition on the anode catalyst. The integrated diesel fuel processor is composed of an autothermal reformer, a desulfurizer, and a post-reformer. The autothermal reforming section in the integrated diesel fuel processor effectively decomposes aromatics, and converts fuel into H 2-rich syngas. The subsequent desulfurizer removes sulfur-containing compounds present in the diesel reformate. Finally, the post-reformer completely removes the light hydrocarbons, which are carbon precursors, in the diesel reformate. We successfully operate the diesel reformer, desulfurizer, and post-reformer as microreactors for about 2500 h in an integrated mode. The degradation rate of the overall reforming performance is negligible for the 2000 h, and light hydrocarbons and sulfur-containing compounds are completely removed from the diesel reformate. © 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.


Baik K.D.,Seoul National University | Hong B.K.,The Fuel Team | Han K.,The Fuel Team | Kim M.S.,Seoul National University
International Journal of Hydrogen Energy | Year: 2012

A correlation between anisotropic bending stiffness of a gas diffusion layer (GDL) and land/channel width ratios of metallic bipolar plates (MBPs) in polymer electrolyte membrane fuel cells has been systematically investigated. I-V performances of the fuel cells with 90° GDLs, whose directions of higher stiffness are perpendicular to the direction of the major flow field, are generally higher than those with 0° GDLs, whose directions of higher stiffness are parallel with the direction of the major flow field. However, the differences of I-V performances and high-frequency resistance values between 0° and 90° GDL cells gradually decrease with increasing land/channel width ratio, because of the reduced anisotropic stiffness effects of the GDLs due to the better support by the MBPs with wider lands. The cross-sectional images of GDLs upon compression indicate that the 0° GDL appears to be more deformed and intruded into channel than the 90° GDL under the narrowest lands, whereas both 0° and 90° GDLs show very little intrusion and deformation under the widest lands. The results clearly explain why some MBPs (i.e., narrower lands) exhibit strong effects of GDL's anisotropic stiffness on cell performances, whereas other MBPs (i.e., wider lands) do not experience such effects. ©, 2012 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.


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

Hydrogen crossover is the main reason for membrane degradation in polymer electrolyte membrane fuel cells (PEMFCs). In this study, local measurements of the hydrogen crossover rate at the cathode in a PEMFC are investigated to analyze the distribution of hydrogen crossover rates under various temperature and relative humidity (RH) conditions. The bipolar plate for the cathode side is specially designed for local measurements. Results show that hydrogen crossover appears to occur mostly near the gas inlet region, and reduced crossover amounts near the outlet region. The hydrogen crossover rates increase with decreasing the nitrogen flow rates at a given section. The effects of temperature and RH on the hydrogen crossover rate over the entire area of the fuel cell are also analyzed and compared with the results of the open circuit voltage (OCV). The results show that the hydrogen crossover rate increases with the increase in both cell temperature and RH, resulting in a decrease in the OCV. © 2012 Elsevier Ltd.


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 | Han K.,The Fuel Team | Kim M.S.,Seoul National University
Renewable Energy | Year: 2014

The effects of the anisotropic bending stiffness of gas diffusion layers (GDLs) on the performance of polymer electrolyte membrane fuel cells with metallic bipolar plates (MBPs), having different channel depths, are investigated. The current-voltage performance of fuel cells with 90° GDLs, whose directions of higher stiffness are perpendicular to the direction of the major flow field, is generally higher than that of cells with 0° GDLs, whose directions of higher stiffness are parallel to the direction of the major flow field. In the shallowest channel, the air pressure drop (δ. P) values of the 90° GDL cells are clearly lower than those of the 0° GDL cells, indicating less intrusion of the 90° GDL into the MBP channels. However, no significant difference appears between the air δ. P values of 0° and 90° GDL cells employing deeper channels. In comparison with other cells employing deeper channels, a dramatic increase in the high-frequency resistance of both the 0° and 90° GDL cells with the shallowest channel is unexpectedly observed, presumably due to the exceptional increase in the hydrogen and air pressure, which may cause more deformation and poor contact status of the GDLs in the cell. The cross-sectional images of GDLs upon compression indicate that the difference of blocked channel area between 0° and 90° GDL cells is much larger in the case of the shallowest channel, resulting in the observed air δ. P, whereas it is substantially negligible for the deepest channel. © 2014 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.


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.


Han I.-S.,The Fuel Team | Lim J.,The Fuel Team | Jeong J.,The Fuel Team | Shin H.K.,The Fuel Team
Renewable Energy | Year: 2013

Serpentine flow-fields are widely used for polymer electrolyte membrane (PEM) fuel cells due to effective water removal. In this study, the effects of serpentine flow-field designs on the performance of a commercial-scale PEM fuel cell stack for micro-CHP (Combined Heat & Power) systems, which use reformed gas as fuel, are investigated by performing both computational fluid dynamics (CFD) simulations and experimental measurements. First, we design four different serpentine flow-fields in which the total channel area (defined as open channel area in this study) of a flow-field plate is altered without changing other design parameters such as the channel cross-sectional area and the channel length. Then, CFD simulations and experimental measurements are performed to assess the performance of each flow-field design. The CFD simulation results show that the current density distributions and average current densities are very insensitive to the open channel area. Thus, the information from the simulations is not sufficient to judge whether the open channel area affects the performance of a PEM fuel cell. On the other hand, the experimental measurements indicate that the performances of four fuel cell stacks, each with one of the four flow-field designs used in the simulations, are considerably different. Increasing the open channel area of a serpentine flow-field improves the performance of the PEM fuel cell up to a certain extent. © 2012 Elsevier Ltd.


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