Hygrothermal aging of Nafion®

Collette, Floraine; Lorentz, Chantal; Gebel, Gérard; Thominette, F.

doi:10.1016/j.memsci.2008.11.048

Cited by 112 publications

(125 citation statements)

References 29 publications

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“…We note that T  could also be related to the thermal history and pretreatment of the membrane, which are known to affect the water-uptake behavior of the membrane. 30,63,68,70,71 Therefore, using the above expressions in Eq.[1], an implicit equation can be written to determine the water uptake of a PFSA membrane,13 Swelling pressureTo solve Eq.[6], one needs to know the swelling pressure function,approaches exist in literature to correlate the swelling pressure to the water volume fraction. [18][19][20]62 In this work, we adopt and modify the geometry-dependent pressure model in reference…”

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confidence: 99%

Understanding the Effects of Compression and Constraints on Water Uptake of Fuel-Cell Membranes

Kusoglu

Kienitz

Weber

2011

J. Electrochem. Soc.

118

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Accurate characterization of polymer-electrolyte fuel cells (PEFCs) requires understanding the impact of mechanical and electrochemical loads on cell components. An essential aspect of this relationship is the effect of compression on the polymer membrane's water-uptake behavior and transport properties. However, there is limited information on the impact of physical constraints on membrane properties. In this paper, we investigate both theoretically and experimentally how the water uptake of Nafion membrane changes under external compression loads. The swelling of a compressed membrane is modeled by modifying the swelling pressure in the polymer backbone which relies on the changes in the microscopic volume of the polymer. The model successfully predicts the water content of the compressed membrane measured through in-situ swelling-compression tests and neutron imaging. The results show that external mechanical loads could reduce the water content and conductivity of the membrane, especially at lower temperatures, higher humidities, and in liquid water. The modeling framework and experimental data provide valuable insight for the swelling and conductivity of constrained and compressed membranes, which are of interest in electrochemical devices such as batteries and fuel cells. † Current Address: W.L. Gore and Associates, 201 Airport Road, Elkton, MD USA ‡ Corresponding author. E-mail address: azweber@lbl.gov Tel: (510) 486-6308. * ECS Member. IntroductionIonomer membranes used in polymer-electrolyte-fuel-cell (PEFC) applications are always subjected to mechanical constraints to some extent due to cell design and clamping loads to reduce contact resistances and seal cells using compression seals. Furthermore, swelling of the membranes due to water uptake results in compressive stresses during cell operation. [1][2][3] Compression in the cell is known to influence membrane stresses, [2][3][4][5][6] transport in gas-diffusion layers (GDL), [7][8][9] and cell resistance. 10 However, the effect of the constraints and mechanical loads on the membrane's water-uptake behavior is yet to be determined due to the difficulty of such measurement. Moreover, due to the lack of the experimental data on the swelling behavior of constrained membranes, mathematical models on water uptake cannot be fully validated. In this work, we aim to investigate how the constraints on the membrane affect its water-uptake behavior and other water-dependent transport properties such as conductivity.In a PEFC, the extent to which the membrane is deformed depends on a number of factors including, but not limited to, geometry of the cell (e.g. land/channel ratio), thickness and stiffness of the cell components (e.g. bipolar plates, gas-diffusion layers (GDLs)), and operating conditions (e.g., humidity). Thus, stresses and pressures in the membrane are not uniform; they depend on location, time, and component material properties. In addition, the membrane itself is subjected to a combination of constraints and mechanical loads: (i) interfacial con...

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confidence: 99%

Understanding the Effects of Compression and Constraints on Water Uptake of Fuel-Cell Membranes

Kusoglu

Kienitz

Weber

2011

J. Electrochem. Soc.

118

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“…It was postulated that this reaction occurs via the formation of aromatic sulfonic anhydrides that evolve to the electrophilic species by heat treatment [44]. The anhydride was several times reported to be present in polymer electrolyte membranes like Nafion [45]. The formation of the anhydride should be favored by the presence of DMSO that enhances the anion reactivity (Scheme 2c).…”

Section: Original Research Papermentioning

confidence: 99%

“…In the frequency region corresponding to hydrogen bond vibrations, apart from a broad band at 3,400 cm -1 from water absorbed, peaks due to methyl groups, belonging to DMSO and derivatives, are observed in the spectrum before the regeneration. The lack in both spectra of a peak at 1,440 cm -1 , typical of condensation products [25,45], indicates the absence in the final material of sulfonic anhydrides (Figure 6b). The characteristic vibrations are reported in Table 3.…”

Section: What Are the Best Treatments To Achieve The Major Quantity Omentioning

confidence: 99%

Cross‐Linking of Sulfonated Poly(ether ether ketone) by Thermal Treatment: How Does the Reaction Occur?

et al. 2013

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The cross-link reaction between macromolecular chains of sulfonated poly(ether ether ketone) (SPEEK) by thermal treatment above 150 degrees C in presence of dimethylsulfoxide (DMSO) is investigated by various techniques, including elemental analysis, acid-base titration, infrared spectroscopy, water uptake (WU) measurements, and thermogravimetry. The conditions of thermal treatment are analyzed. The cross-linking reaction occurs in at least three more or less activated and deactivated positions with different activation energies, leading to different time dependencies of the cross-link reaction. The role of residual solvent DMSO is studied particularly: the cross-linking depends significantly on the amount of solvent in the membranes. Implications on WU and thermal stability are of particular importance for the development of high performance proton-conducting membranes

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“…Among commercial perfluorosulfonate ionomer (PFSI) electrolytes, Nafion shows the best performance in terms of durability, high proton conductance, and stability [Collette 2009;. Results from previous work directly suggest that the ionic conductivity of a Nafion membrane is proportional to the concentration of free proton sites ].…”

Section: Motivationmentioning

confidence: 99%

Final Technical Report: Effects of Impurities on Fuel Cell Performance and Durability

Goodwin¹,

Colón-Mercado²,

Hongsirikarn³

et al. 2011

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EXECUTIVE SUMMARYThe main objectives of this project were to investigate the effect of a series of potential impurities on fuel cell operation and on the particular components of the fuel cell MEA, to propose (where possible) mechanism(s) by which these impurities affected fuel cell performance, and to suggest strategies for minimizing these impurity effects. This project was carried out primarily at Clemson University and the Savannah River National Lab. Fuel cell investigations were done at SRNL while all investigations of the MEA components were carried out at Clemson. Meetings took place weekly at Clemson University and at SRNL with the respective project participants. Joint meetings between researchers at Clemson and SRNL took place quarterly, on average. In addition, frequent communications among project participants took place via e-mail and telephone discussions. On other occasions the researchers met with the technical staff of John Deere for discussions. At least one member of our team routinely participated in the DOE-Sponsored Joint Hydrogen Quality Task Force Meetings (usually conducted monthly).The nature and concentrations of impurities investigated and their impact on fuel cell performance and individual components are given in the table below. The negative effect on Pt/C was to decrease hydrogen surface coverage and hydrogen activation at fuel cell conditions. The negative effect on Nafion components was to decrease proton conductivity, primarily by replacing/reacting with the protons on the Bronsted acid sites of the Nafion.Even though already well known as fuel cell poisons, the effects of CO and NH 3 were studied in great detail early on in the project in order to develop methodology for evaluating poisoning effects in general, to help establish reproducibility of results among a number of laboratories in the U.S. investigating impurity effects, and to help establish lower limit standards for impurities during hydrogen production for fuel cell utilization.New methodologies developed included (1) a means to measure hydrogen surface concentration on the Pt catalyst (HDSAP) before and after exposure to impurities, (2) a way to predict conductivity of a Nafion membranes exposed to impurities using a characteristic acid catalyzed reaction (methanol esterification of acetic acid), and, more importantly, (3) application of the latter technique to predict conductivity on Nafion in the catalyst layer of the MEA. H 2 -D 2 exchange was found to be suitable for predicting hydrogen activation of Pt catalysts.Using a combination of standard catalyst characterization techniques, a structure sensitive catalytic reaction technique (cyclopropane hydrogenolysis), and reaction and transport modeling led to the finding that in the catalyst layer (essentially Nafion/Pt/C) the following best describes the structure. Pt is highly dispersed on the C support, but primarily in the meso-and macropores. The Nafion (ca. 30 wt%) resides primarily on the external surface of the C support where it blocks significant numbers ...

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Hygrothermal aging of Nafion®

Cited by 112 publications

References 29 publications

Understanding the Effects of Compression and Constraints on Water Uptake of Fuel-Cell Membranes

Understanding the Effects of Compression and Constraints on Water Uptake of Fuel-Cell Membranes

Cross‐Linking of Sulfonated Poly(ether ether ketone) by Thermal Treatment: How Does the Reaction Occur?

Final Technical Report: Effects of Impurities on Fuel Cell Performance and Durability

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