Time-dependent mechanical response of a composite PFSA membrane

Khattra, Narinder Singh; Lu, Zongwen; Karlsson, Anette M.; Santare, Michael H.; Busby, F. Colin; Schmiedel, T.

doi:10.1016/j.jpowsour.2012.11.116

Cited by 43 publications

(36 citation statements)

References 35 publications

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“…Distinct from the isotropic swelling of Nafion 212 membrane, Nafion XL membrane exhibits significant swelling anisotropy, both in the plane and thickness directions. The high thickness/in-plane swelling ratio of ~14 is comparable to, but slightly higher than 10, the value estimated for other ePTFE reinforced PFSA membranes [28][29][30]. Overall, Nafion XL swells less in plane; 1% in the machine direction (MD), and 5% in the transverse direction (TD), which are very close to the values reported by DuPont [35].…”

Section: Swelling and Water Uptakesupporting

confidence: 82%

“…Gore & Associates, Inc., which is a composite ionomer membrane reinforced by a thin microporous expanded polytetrafluorothylene (ePTFE) layer [21,22]. [25,28,29] Such swelling anisotropy was shown to be critical in reducing the swelling-induced mechanical stresses during cell operation, especially under cycling conditions [7,28,30]. The pores in the ePTFE matrix are also filled with ionomer to enable a continuous transport pathway across its thickness.…”

Section: Introductionmentioning

confidence: 99%

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Structure/property relationship of Nafion XL composite membranes

Shi

Weber

Kusoglu

2016

Journal of Membrane Science

145

138

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Perfluorosulfonic-acid (PFSA) ionomer membranes (most commonly Nafion ® ) are currently the prototypical proton-exchange-membrane in polymer-electrolyte fuel cells (PEFCs), for which durability still represents a technical barrier to their commercialization. In an effort to address the durability demands, PFSA membranes with reinforcement and/or stabilizers have become of great interest as they have demonstrated superior durability in PEFCs compared to their unreinforced analogues. One such particular membrane that is tailored for enhanced durability and commonly employed in PEFCs is Nafion XL, a Nafion-based ionomer membrane with mechanical reinforcement and chemical stabilizers. Despite an increasing number of recent studies demonstrating its improved lifetime in accelerated stress testing (AST), its structure and transport properties have not been investigated in a systematic fashion. In this paper, we report water uptake, dimensional change, conductivity, and mechanical properties of Nafion XL membrane, as well as its strong anisotropy, in comparison to (unreinforced) Nafion 212 membrane.Moreover, water-domain spacing and crystallinity of Nafion XL membrane, determined from small-and wide-angle X-ray scattering (SAXS/WAXS) experiments, are correlated with the measured properties to establish a structure/property relationship, and discussed within the context of composite materials. It is also found that (pre)conditioning of the membrane by heating in water at different temperatures could have significant impacts on its structure/property relationship, in particular, the mechanical stability and conductivity, which were related to morphological changes observed from microscopy 2 studies. The findings reported here not only provide a new dataset that can be used for PEFC performance and durability modeling but also benefit the efforts on developing composite ionconductive membranes. 1.Highlights  The composite Nafion XL membrane's structure/property relationship is investigated  Impact of pretreatment on membrane's transport and mechanical properties are shown  Membrane's composite morphology are revealed through TEM, SEM and SAXS/WAXS

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Section: Swelling and Water Uptakesupporting

confidence: 82%

Section: Introductionmentioning

confidence: 99%

Structure/property relationship of Nafion XL composite membranes

Shi

Weber

Kusoglu

2016

Journal of Membrane Science

145

138

View full text Add to dashboard Cite

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“…Such a phenomenon is in agreement with the observation made by Tang et al. who found that the break stresses of GORE‐SELECT ® membrane in MD and TD were similar. As the Nafion™ XL composite membrane is anisotropic in‐plane, the similar break stresses seem counter‐intuitive at a first glance.…”

Section: Resultsmentioning

confidence: 47%

“…Thus, more load is required for PB membranes to deform to the same extent as AsR membranes, accounting for the higher strain‐hardening modulus and lower break strain of PB membranes in Figure . Even though higher strength of reinforcement composite membranes has been reported in literature, this study delineates the deformation mechanisms and therefore accounting for their improved mechanical durability.…”

Section: Resultsmentioning

confidence: 99%

“…The relatively stiff porous reinforcement layer not only reduces in-plane swelling which induces mechanical stress during humidity cycling, but also increases the mechanical strength [12]. Higher strength [13][14][15], toughness [16,17] and improved resistance to creep and fatigue [18,19] of the reinforced composite membrane were observed. While the high toughness of the reinforced membrane was attributed to the blunting effect of the reinforcement layer [16], the improved -[ * ] Corresponding author, swshi@tju.edu.cn { These authors contributed equally to this work fatigue crack propagation resistance was ascribed to the fiber bridging effect that reduced the stress actually experienced at the crack tip [19].…”

Section: Introductionmentioning

confidence: 99%

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Effect of Pretreatment on Microstructure and Mechanical Properties of Nafion™ XL Composite Membrane

et al. 2019

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As an ion‐conductive polymer electrolyte, Nafion™ XL composite membrane is used to meet the requirement for cost reduction, performance and durability improvement in polymer electrolyte fuel cells. While significant durability is observed for Nafion™ XL membrane, the mechanisms of improved mechanical durability, especially the impact induced by pretreatment, is still left unexplored. In this paper, ex situ mechanical tests of pretreated membranes are carried out, including tensile, fracture and fatigue crack propagation tests, to unravel the complex interplay between strength, fracture toughness and cyclic hygrothermal stress that controls the mechanical durability. Pretreatment increases strain‐hardening modulus at the expense of reduced ductility, while the break stress is not affected. Results from in situ SEM tensile tests reveal that pretreatment increases the orientation resistance during tension, leading to increased stress responses. In addition, the fracture resistance and fatigue crack propagation resistance increase after pretreatment, which is ascribed to increased membrane stiffness and reinforcement fiber reorientation, respectively. From a microscopic point of view, fibers along the cross‐sectional reinforcement layer collapse, corresponding to fiber reorientation at a smaller size scale and accounting for the above increased resistance. The findings reported here will provide more insights into the mechanical durability of composite ion‐conductive membranes.

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Effect of Water Transport on Swelling and Stresses in PFSA Membranes

et al. 2014

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The mechanical durability of membranes used in proton exchange membrane fuel cells (PEMFC) is directly linked to the stresses that evolve in the membrane during fuel cell operation. The stresses are primarily induced due to the swelling of the membrane as it absorbs water, within the mechanical constraints in the fuel cell assembly. Thus, in order to predict the membrane stresses, the water content in the perfluorosulphonic acid (PFSA) membranes is determined numerically via three different absorption models based on experimentally determined water uptake data from the literature. Two models are based on a single, humidity-dependent Fickian transport coefficient for the bulk PFSA membrane. In the third, two transport properties are modeled to account for a possible difference in transport resistance between the bulk membrane and the outer surface. The membrane sorption behaviors characterized from these three models are then independently incorporated in a representative fuel cell finite element model and subjected to a standard relative humidity (RH) protocol designed for measuring mechanical durability of PEMFCs. The results show that the sorption behavior has a significant effect on the membrane stresses and therefore, may impact the lifetime of the membrane.

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Time-dependent mechanical response of a composite PFSA membrane

Cited by 43 publications

References 35 publications

Structure/property relationship of Nafion XL composite membranes

Structure/property relationship of Nafion XL composite membranes

Effect of Pretreatment on Microstructure and Mechanical Properties of Nafion™ XL Composite Membrane

Effect of Water Transport on Swelling and Stresses in PFSA Membranes

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