FUELCELL2006-97271 EXPERIMENTAL INVESTIGATION OF LIQUID WATER FORMATION AND TRANSPORT IN A TRANSPARENT SINGLE-SERPENTINE PEM FUEL CELL

ABSTRACT Liquid water formation and transport was investigated by direct experimental visualization in an operational transparent single-serpentine PEM fuel cell. We examined the effectiveness of various gas diffusion layer (GDL) materials in removing water away from the cathode and through the flow field over a range of operating conditions. Complete polarization curves as well as time evolution studies after step changes in current draw were obtained with simultaneous liquid water visualization within the transparent cell. At similar current density (i.e. water production rate), lower level of cathode flow field flooding indicated that liquid water had been trapped inside the GDL pores and catalyst layer, resulting in lower output voltage. No liquid water was observed in the anode flow field unless cathode GDLs had a microporous layer (MPL). MPL on the cathode side creates a pressure barrier for water produced at the catalyst layer. Water is pushed across the membrane to the anode side, resulting in anode flow field flooding close to the H 2 exit

Degradation aspects of water formation and transport in Proton Exchange Membrane Fuel Cell: A review

This review paper summarises the key aspects of Proton Exchange Membrane Fuel Cell (PEMFC) degradation that are associated with water formation, retention, accumulation, and transport mechanisms within the cell. Issues related to loss of active surface area of the catalyst, ionomer dissolution, membrane swelling, ice formation, corrosion, and contamination are also addressed and discussed. The impact of each of these water mechanisms on cell performance and durability was found to be different and to vary according to the design of the cell and its operating conditions. For example, the presence of liquid water within Membrane Electrode Assembly (MEA), as a result of water accumulation, can be detrimental if the operating temperature of the cell drops to sub-freezing. The volume expansion of liquid water due to ice formation can damage the morphology of different parts of the cell and may shorten its life-time. This can be more serious, for example, during the water transport mechanism where migration of Pt particles from the catalyst may take place after detachment from the carbon support. Furthermore, the effect of transport mechanism could be augmented if humid reactant gases containing impurities poison the membrane, leading to the same outcome as water retention or accumulation. Overall, the impact of water mechanisms can be classified as aging or catastrophic. Aging has a long-term impact over the duration of the PEMFC life-time whereas in the catastrophic mechanism the impact is immediate. The conversion of cell residual water into ice at sub-freezing temperatures by the water retention/ accumulation mechanism and the access of poisoning contaminants through the water transport mechanism are considered to fall into the catastrophic category. The effect of water mechanisms on PEMFC degradation can be reduced or even eliminated by (a) using advanced materials for improving the electrical, chemical and mechanical stability of the cell components against deterioration, and (b) implementing effective strategies for water management in the cell

Seciranje organov sesalcev v osnovi in srednji soli ter njihovo mnenje o sekciji v razredu

This article describes the results of a study that investigated the use of the dissection of organs in anatomy and physiology classes in Slovenian lower and upper secondary schools. Based on a sample of 485 questionnaires collected from Slovenian lower and upper secondary school students, we can conclude that dissection of mammalian organs during the courses on Human Anatomy would be a preferred activity for the majority of them. Opinions on such practices are positive, and only a minority of students would prefer to opt out. However, the practice is performed only occasionally in regular classes, or even omitted, and a number of students never participate in it. According to the results, we can suggest the dissection of mammalian organs in combination with alternatives, such as 3D models and virtual laboratories, as a preferred strategy to increase knowledge of anatomy and to raise interest in science. However, students should know that the organs they are dissecting were dedicated to human consumption, or are waste products in these processes. Opt-out options should be provided for those who do not want to participate in such activities. (DIPF/Orig.

In-situ two-phase flow investigation of Proton Exchange Membrane (PEM) electrolyzer by simultaneous optical and neutron imaging

11th Polymer Electrolyte Fuel Cell Symposium (PEFC) Under the Auspices of the 220th Meeting of the ECS -- OCT, 2011 -- Boston, MAWOS: 000309598800030In proton exchange membrane (PEM) electrolyzers, oxygen evolution in the anode and flooding due to water cross-over results in two distinct two-phase transport conditions, and these two phenomena were found to strongly affect the performance. A comprehensive understanding of two-phase flow in PEM electrolyzer is required to increase efficiency and aid in material selection and flow field design. In this study, two-phase transport in an electrolyzer cell is visualized by simultaneous neutron radiography and optical imaging. Optical and neutron data were used in a complementary manner to aid in understanding the two-phase flow behavior. The behavior of the gas bubbles was investigated and two different gas bubble evolution and departure mechanisms are found. It was also found that there is a strong non-uniformity in the gas bubble distribution across the active area, due to buoyancy and proximity to the water and purge gas inlet.ECS, Energy Technol (ETD), Phys & Analyt Electrochem (PAED), Battery (BATT), Ind Electrochem & Electrochem Engn (IEEE), Corros (CORR)Scientific and Research Council of Turkey (TUBITAK); National Science Foundation [CBET-0748063]; U.S. Department of Commerce; NIST Ionizing Radiation Division; Director's Office of NIST; NIST Center for Neutron Research; Department of Energy [DEAI01-01EE50660]Omer F. Selamet would like to thank the Scientific and Research Council of Turkey (TUBITAK) for financial support for this research. Financial support for this work from the National Science Foundation (CBET-0748063) is gratefully acknowledged. We thank professors Ajay K. Prasad and Suresh G. Advani of the University of Delaware for their assistance with the experimental setup. The authors thank Elias Baltic of the NIST for his technical help during the experiments in the NIST. This work was supported by the U.S. Department of Commerce, the NIST Ionizing Radiation Division, the Director's Office of NIST, the NIST Center for Neutron Research, and the Department of Energy through Interagency Agreement No. DEAI01-01EE50660. We also thank to Richard S. Fu for his help during the data analysis

Two-phase flow in a proton exchange membrane electrolyzer visualized in situ by simultaneous neutron radiography and optical imaging

WOS: 000319232500036In proton exchange membrane (PEM) electrolyzers, oxygen evolution in the anode and flooding due to water cross-over in the cathode yields two distinct two-phase transport conditions which strongly affect the performance. Two-phase transport in an electrolyzer cell is visualized by simultaneous neutron radiography and optical imaging. Optical and neutron data are used in a complementary manner to aid in understanding the two-phase flow behavior. Two different patterns of gas-bubble evolution and departure are identified: periodic growth/removal of small bubbles vs. prolonged blockage by stagnant large bubbles. In addition, the bubble distribution across the active area is not uniform due to combined effects of buoyancy and proximity to the inlet. The effects of operating parameters such as current density, temperature and water flow rate on the two-phase distribution are investigated. Higher water accumulation is detected in the cathode chamber at higher current density, even though the cathode is purged with a high flow rate of N-2. The temperature is found to affect the volume of water; higher temperature yields less water and more gas volume in the anode chamber. Higher temperature also enhanced the water transport in the cathode chamber. Finally, water transported through the membrane to the cathode reduced the cell performance by limiting the hydrogen mass transport. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.Scientific and Research Council of Turkey (TUBITAK); National Science Foundation [CBET-0748063]; U.S. Department of Commerce; NIST Radiation and Biomolecular Physics Division; Director's Office of NIST; NIST Center for Neutron Research; Department of Energy [DEAI01-01EE50660]Omer F. Selamet would like to thank the Scientific and Research Council of Turkey (TUBITAK) for financial support for this research. Financial support for this work from the National Science Foundation (CBET-0748063) is gratefully acknowledged. This work was supported by the U.S. Department of Commerce, the NIST Radiation and Biomolecular Physics Division, the Director's Office of NIST, the NIST Center for Neutron Research, and the Department of Energy through Interagency Agreement No. DEAI01-01EE50660. We thank professors Ajay K. Prasad and Suresh G. Advani of the University of Delaware for their assistance with the experimental setup and equipment loan, Eli Baltic of the NIST for his help during the experiments in the NIST, and Richard S. Fu for his help with data analysis