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

Spatially resolved degradation during startup and shutdown in polymer electrolyte membrane fuel cell operation

International audience• Degradation due air/air operation due to startup and shutdown in fuel cell studied. • The effect of platinum loading, and carbon support material is studied. • A segmented cathode hardware is utilized to study the effect along the flow field. • In-situ and ex-situ characterization were correlated to elucidate the degradation. • Limiting the anode's ability to reduce oxygen to water is key to mitigating loss. A B S T R A C T Polymer electrolyte membrane fuel cells have durability limitations associated with the startup and shutdown of the fuel cell, which is critical for real-world vehicle commercialization. During startup or shutdown, there exists an active region (hydrogen/air) and a passive region (air/air) between the cell inlet and outlet. Internal currents are generated in the passive region causing high-potential excursion in the cathode leading to accelerated carbon corrosion. In this study, a segmented cathode hardware is used to evaluate the effect of platinum loading on both cathode and anode, and carbon support material on degradation due to repeated series of startups or shutdowns. In situ losses in the performance and electrochemical surface area were measured spatially, and ex situ analysis of the catalyst layer thickness and platinum particle size was performed to understand the effect of startup or shutdown on different membrane electrode assembly materials. Startup degrades the region near anode outlet more, while shutdown degrades the region near anode inlet more compared to the rest of the electrode. While various system mitigation strategies have been reported in the literature to limit this degradation, one materials mitigation strategy is to limit the anode's ability to reduce oxygen to water through increasing the ratio of platinum loading in the cathode to the anode, or by using a bi-functional catalyst

Phase-Change-Related Degradation of Catalyst Layers in Proton-Exchange-Membrane Fuel Cells

Understanding and optimizing water and thermal management in the catalyst layer of proton-exchange-membrane fuel cells is crucial for performance and durability improvements. This is especially the case at low temperatures, where liquid water and even ice may exist. In this article, the durability of a traditional Pt/C dispersed and a nanostructure thin film (NSTF) membrane-electrode assembly (MEA) are examined under wet/dry and freeze/thaw cycles using both in situ and ex situ experiments. Multiple isothermal cold starts result in a performance degradation for the dispersed MEA, while no such a degradation is found in the NSTF. The results are consistent with stand-alone MEA tests, wherein the dispersed catalyst layer results in an exponential increase in the number and size of cracks until it delaminates from the membrane due to the impact of the freeze/thaw process within the catalyst-layer pores. The NSTF catalyst layer shows minimal crack generation without delamination since the ice forms on top of the layer. The results are useful for understanding degradation due to phase-change containing cycles. (c) 2013 Elsevier Ltd. All rights reserved.X111514sciescopu

Internal Currents, CO2 Emissions and Decrease of the Pt Electrochemical Surface Area during Fuel Cell Start-Up and Shut-Down

International audienceThis work explores the links between internal currents measured during fuel cell start-up (SU) and shut-down (SD) and the CO2 emissions in the cathode exhaust gases associated with the oxidation of the electrode carbon support. The total charge exchanged between the active and passive regions of a cell appears to be a function of the common residence time of air (or nitrogen) and hydrogen in the anode compartment during SU/SD operation. Both the CO2 emissions and the charges exchanged between the active and passive regions of the cell increase with this residence time. However, the complete oxidation of carbon to CO2 does not seem to be the main contribution to the reverse currents

Transparent PEM Fuel Cells for Direct Visualization Experiments

This paper reviews some of the previous research works on direct visualization of water behavior inside proton exchange membrane (PEM) fuel cells using a transparent single cell. Several papers which have employed the method have been selected and summarized, and a comparison between the design of the cell, materials, methods, and visual results are presented. The important aspects, advantages of the method, and a summary on the previous investigations are discussed. Some initial works on transparent PEM fuel cell design using a single serpentine flow-field pattern are described. The results show that the direct visualization via transparent PEM fuel cells could be one potential technique for investigating the water behavior inside the channels and a very promising way forward to provide useful data for validation in PEM fuel cell modeling and simulation

Anode-Design Strategies for Improved Performance of Polymer-Electrolyte Fuel Cells with Ultra-Thin Electrodes

We report results of systematic, holistic, diagnostic, and cell studies to elucidate the mechanistic role of the experimentally determined influence of the anode gas-diffusion layer (GDL) on the performance of ultra-thin electrode polymer-electrolyte fuel cells, which can further enable fuel-cell market penetration. Measurements of product water balance and in situ neutron imaging of operational membrane-electrode-assembly water profiles demonstrate how improved performance is due to a novel anode GDL fiber-density modulated structure at the micrometer scale that removes water preferentially out of the anode, a key strategy to manage water in these cells. The banded structure results in low transport-resistance pathways, which affect water-droplet removal from the GDL surface. This interfacial effect is unexpectedly shown to be critical for decreasing overall water holdup throughout the cell. These studies demonstrate a new material paradigm for understanding and controlling fuel-cell water management and related high-power technologies or electrodes where multiphase flow occurs. Very thin electrodes enable high power density in electrochemical technologies, yet their thinness engenders issues related to buildup of products (e.g., water in polymer-electrolyte fuel cells [PEFCs]). The article explores an unexpected materials solution to the problem, which highlights the need to study such complicated systems in a holistic manner of a complete cell due to the nonlinearities existent in the highly coupled physical phenomena. The improved performance is due to an inherent unintentional manufacturing heterogeneity in the cell backing layer, which mainly affects its surface properties. With this knowledge, one can now engineer and optimize these critical heterogeneities for different architectures. The findings are relevant to those working on materials for electrochemical energy conversion and represent new key knowledge that can have significant impact in PEFCs and related electrochemical cells, especially where multiphase flow occurs. High-power electrodes in electrochemical technologies (e.g., fuel cells) typically require ultra-thin catalyst layers, which, especially when multiphase flow exists, exhibit mass-transport limitations. These have been mitigated through new backing layer structures and nontraditional removal of water out of the anode side of the cell for a new design and operation paradigm