Constitutive response and mechanical properties of PFSA membranes in liquid water

Kusoglu, Ahmet; Tang, Yaliang; Lugo, Melissa; Karlsson, Anette M.; Santare, Michael H.; Cleghorn, Simon; Johnson, W.B.

doi:10.1016/j.jpowsour.2009.08.010

Cited by 65 publications

(107 citation statements)

References 75 publications

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“…12 and 14). We have observed a similar phenom ® enon while studying the time-independent behavior of the Nafion 112 membrane [22]. As we did in that study, we attribute this abrupt change in properties to a significant increase in water absorption when the membrane is taken from fully saturated humid air to a liquid water environment [23e25].…”

Section: Characteristic Mechanical Propertiessupporting

confidence: 58%

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An experimental investigation of strain rate, temperature and humidity effects on the mechanical behavior of a perfluorosulfonic acid membrane

Lugo

Santare

et al. 2012

Journal of Power Sources

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Section: Characteristic Mechanical Propertiessupporting

confidence: 58%

“…These measured in-plane dimensional changes along with an assumption of swelling isotropy, which is supported by our previous work [13,22], are used to calculate the true stress and true strain values in the following results. Fig.…”

Section: Swelling Behaviormentioning

confidence: 85%

An experimental investigation of strain rate, temperature and humidity effects on the mechanical behavior of a perfluorosulfonic acid membrane

Lugo

Santare

et al. 2012

Journal of Power Sources

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“…However, the observed increase in chemical decomposition after 1 MPa is likely to be due to the mechanical loads, not the change in contact resistance or exposure area (including the minor thickness changes of ∼5% with compression (Figure 3)). It should also be noted that, in water, pressures greater than 3 MPa could induce plastic deformation, 4,25,27 which may dissipate the mechanical energy differently and impact the effect of stresses on chemical degradation. Another phenomenon that could be responsible for the non-monotonic pressure dependence is the change in membrane's stress-strain response due to degradation (Figure 3), which would gradually increase the strain in the degrading membrane, even at the same pressure.…”

Section: Resultsmentioning

confidence: 99%

Effect of Mechanical Compression on Chemical Degradation of Nafion Membranes

Kusoglu

Calabrese

Weber

2014

ECS Electrochemistry Letters

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The effect of compression on the chemical degradation of Nafion is investigated. Results indicate a nonlinear dependence of chemical degradation on compression level, with a slight decrease at 1 MPa and then increase up to 10 MPa. The results confirm the synergistic nature of mechanical effects on chemical fuel-cell membrane degradation, which are expected to occur in operando. The impact of compression is also shown to change the nano-domain structure, consistent with the increase in chemical decomposition. Thus, deformation energy accumulated in the membrane due to mechanical loads seemingly accelerates the chemical reactions driving the decomposition of the polymer membrane. © 2014 The Electrochemical Society. [DOI: 10.1149/2.008405eel] All rights reserved. Perfluorinated sulfonic-acid (PFSA) membranes are the most widely studied class of ionomer membrane for polymer-electrolyte fuel-cell (PEFC) applications, with Nafion being the prototypical PFSA. Membrane degradation in PEFCs due to chemical and mechanical stressors represents a barrier to realizing the necessary fuelcell lifetimes for commercialization.1 During cell operation, chemical decomposition of the membrane can occur due to attack of polymer moieties by radicals produced during operation.1-3 These radicals are produced under chemical stressors, such as high potentials (i.e., open-circuit voltage (OCV) conditions). In addition to chemical degradation, membranes can fail due to loss of mechanical integrity caused by mechanical stressors. These latter stressors originate from the deformation of the membrane due to cell assembly (constraint) and subsequent operational stresses driven by the hydration/dehydration of the constrained membrane. [1][2][3][4][5][6][7] To understand the impact of various stressors, accelerated stress tests (ASTs) are typically conducted with the aim of enhancing a single failure mode, 1,2,8 with Fenton's tests accelerating chemical degradation 7,9-14 and relative-humidity (RH) cycling used for mechanical degradation. [1][2][3]6,8,15 However, failure mechanisms in operando are controlled by combination of chemical and mechanical stressors, which makes understanding any synergistic chemical/mechanical interactions of great importance.Chemical degradation is believed to occur when the polymer is attacked by radicals. 1,[9][10][11][12][13][14]16 Fenton's Test is commonly employed to study the chemical-decomposition behavior of a membrane by monitoring the release of fluoride ions from the PFSA membrane's fluorocarbon chains. 1,7,[9][10][11][12][13][14] While it is known that chemical degradation changes the membrane's mechanical and other properties, 7,17,18 it is unknown as to whether concurrent mechanical and chemical stressors act independently or in concert to alter membrane degradation rates. Such combined stresses are expected to occur under actual operation due to simultaneous load and humidity changes. Thus, it is worthwhile to explore chemical degradation in the presence of mechanical loads to gain an increased understa...

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“…37 Interestingly, when the membrane is in liquid water as com pared to a 90-95% RH environment, the fracture energy of the membrane decreases significantly such that a smooth humid-to-wet transition of the data and the corresponding hygrothermal master curve could not be obtained in the work presented by Patankar et al 22 This rapid transition in the fracture energy of the membrane upon immersion in water is consistent with earlier observations on the stressstrain behavior of PFSA membranes. 38,39 The membrane's deformation behavior in humid air was found to exhibit characteristic features of semicrystalline polymers with dis tinctive features such as the onset of plasticity, 38,39 whereas in liquid water, an elastomeric stress-strain response with very low yield strength is observed. 38 When the environment changes from saturated air to liquid water, almost a twofold increase is observed in the water content in the membrane.…”

Section: Introductionmentioning

confidence: 99%

“…38,39 The membrane's deformation behavior in humid air was found to exhibit characteristic features of semicrystalline polymers with dis tinctive features such as the onset of plasticity, 38,39 whereas in liquid water, an elastomeric stress-strain response with very low yield strength is observed. 38 When the environment changes from saturated air to liquid water, almost a twofold increase is observed in the water content in the membrane. Higher swelling, combined with the possibility of morpholog ical changes in water, [40][41][42] might alter the structure of the membrane to such an extent that an entirely different hy pothesis is needed to understand the origins of the changes in properties during vapor-to-liquid transition.…”

Section: Introductionmentioning

confidence: 99%

Aspects of fatigue failure mechanisms in polymer fuel cell membranes

Kusoglu

Santare

Karlsson

2011

J Polym Sci B Polym Phys

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The swelling‐driven fatigue behavior of polymer fuel cell membranes during relative humidity (RH) cycling is investigated. In particular, swelling‐induced membrane stresses are obtained from a numerical model simulating fuel cell RH cycle tests, and compared to the lifetimes obtained experimentally from tests conducted in the absence of electrochemical effects. A strong correlation between the lifetimes of the membranes in the actual tests and model results is obtained. In general, higher RH (or swelling) amplitude results in larger stress amplitudes and shorter lifetime, that is, fewer cycles to failure. Tensile stresses are needed for forming local cavities in the membrane, which may eventually lead to craze formation. Cavitation is less likely to occur in compressed membrane at high humidities. The stress–lifetime plots for polymer fuel cell membranes exhibit similar features to those observed for other polymers. The crazing criterion for polymers suggests that craze initiation during RH cycling is more likely to occur in the low compression regions, such as under the channels, which is in agreement with experimental observations. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1506–1517, 2011

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Constitutive response and mechanical properties of PFSA membranes in liquid water

Abstract: • Depanment ofM~hanical fnginl'<'rlng. Univf'rsily a/De/awarf'. Newark. Of 19716. United SImes ~Core fuel Cell Ttchnologies.

Cited by 65 publications

References 75 publications

An experimental investigation of strain rate, temperature and humidity effects on the mechanical behavior of a perfluorosulfonic acid membrane

An experimental investigation of strain rate, temperature and humidity effects on the mechanical behavior of a perfluorosulfonic acid membrane

Effect of Mechanical Compression on Chemical Degradation of Nafion Membranes

Aspects of fatigue failure mechanisms in polymer fuel cell membranes

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