Viscoelastic properties of Nafion at elevated temperature and humidity

Satterfield, M. Barclay; Benziger, J.

doi:10.1002/polb.21608

Cited by 131 publications

(162 citation statements)

References 46 publications

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“…Exposing the AEMS to humidity allows the polymer to uptake water, which has a plasticizing effect. 25,28,35 The water plasticizer generally reduces the elastic modulus, increases elongation, and decreases the stress to break. The change in mechanical properties due to humidity is dependent on the amount of water taken up by the polymer.…”

Section: Resultsmentioning

confidence: 99%

“…10 Sorption of water into the polymer can have a plasticizing effect on the membrane, which is quantified by increases in elasticity and elongation as well as a reduction in membrane strength. 18,25 Generally, water uptake is proportional to IEC, and the water uptake can be translated to the number of water molecules associated with each cationic group. Accurately measuring water uptake at different relative humidities is critical to understanding how mechanical properties change under different environmental conditions.…”

Section: Resultsmentioning

confidence: 99%

“…3,18,25 However, because AEM development is still preliminary, basic mechanical testing is not standardized and comparing mechanical properties of AEMs is difficult. In this study, the extensional properties of three well-studied AEMs were investigated under different temperature and humidity conditions.…”

Section: H678mentioning

confidence: 99%

See 2 more Smart Citations

Mechanical Characterization of Anion Exchange Membranes by Extensional Rheology under Controlled Hydration

Vandiver

Caire

Carver

et al. 2014

J. Electrochem. Soc.

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Alkali anion exchange membrane (AEM) based devices have the potential for electrochemical energy conversion using inexpensive catalysts and a variety of fuel types. Membrane stability and anion transport must be improved in AEMs before these devices can be fully realized. Mechanical failure of the membrane can contribute to failure of the device, thus membrane durability is critical to overall system design. Here, a study of the mechanical properties of three well-established AEMs uses a modified extensional rheometer platform to simulate tensile testing using small membrane samples. Mechanical properties were tested at 30 and 60 • C under dry or water saturated gas conditions. Water in the membrane has a plasticizing effect, softening the membrane and reducing strength. PEEK membrane reinforcement limits swelling producing negligible softening and only a 9% decrease in strength from dry to hydrated conditions at 30 • C. Higher cation concentration increases water uptake resulting in significant softening, a 57% reduction in Young's modulus, and a 67% reduction in strength when hydrated at 30 • C. In a working electrochemical device, AEMs must maintain integrity over a range of temperatures and hydrations, making it critical to considering mechanical properties when designing new membranes. Polymer electrolyte membrane fuel cells and electrolyzers are potentially disruptive technologies that will replace traditional heat engines such as internal combustion engines for transportation applications, portable electronics, and are scalable to larger energy storage facilities. Polymer electrolyte membrane fuel cells are suitable for transportation applications due to their low temperature start-up and operation, high power density, and quick refueling.1-3 Proton exchange membranes (PEMs) have dominated polymer electrolyte membrane fuel cell development in the last several decades, resulting in the development of relatively stable, well performing membranes.1-4 Current PEM fuel cells remain cost prohibitive due to high catalysts costs, as well as long-term durability issues. 3,5,6 Anion exchange membranes (AEMs) can also be utilized in polymer electrolyte membrane devices and have several potential benefits over PEMs. AEM fuel cells benefit from increased kinetics in an alkali media allowing more complex fuels then hydrogen and have the potential to utilize non-platinum catalysts to reduce costs. 7-11However, a number of challenges must be overcome before AEMs reach the performance and durability necessary for fuel cells and other electrochemical energy conversion devices. Hydroxide present in the AEM degrades many of the proposed cationic groups and some polymer backbones, making development of chemically stable AEMs difficult. 9,11,12 Additionally, transport of hydroxide in AEMs is inherently slower than protons in PEMs, 13 to compensate, the concentration of ionic groups is often increased in AEMs.8 Increasing ion concentration in AEMs increases water sorption in the polymer and can result in significant dimensional...

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Mechanical Characterization of Anion Exchange Membranes by Extensional Rheology under Controlled Hydration

Vandiver

Caire

Carver

et al. 2014

J. Electrochem. Soc.

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“…[8][9][10][11] The second type of stress encountered in an operating fuel cell is the mechanical stress, which originates due to compression, humidity cycling, and inhomogeneous features of the membrane electrode assembly through the mechanisms of fatigue and creep. [12][13][14][15][16] Thermal stress mainly acts as an accelerator of chemical and mechanical degradation provided that the temperature is kept within the design specifications of the membrane. In order to develop durable fuel cells and operating protocols with mitigated degradation rates, a thorough fundamental understanding of the various degradation mechanisms is essential.…”

mentioning

confidence: 99%

Progression in the Morphology of Fuel Cell Membranes upon Conjoint Chemical and Mechanical Degradation

Venkatesan

Lim

Holdcroft

et al. 2016

J. Electrochem. Soc.

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Ionomer membranes used to separate the electrodes in polymer electrolyte fuel cells are known to degrade both chemically and mechanically during regular fuel cell operation and may ultimately result in lifetime-limiting failure. The objective of the present work is to understand the effects of combined chemical and mechanical stresses on the mesoscale morphology of the membrane and its role in the overall degradation process. The mesoscale effects of sulfonic acid group loss and fluoride release on the phase segregated morphology of the membrane are analyzed using contrast-enhanced transmission electron microscopy and energy dispersive X-ray spectroscopy. The end-of-life ionic domain size of the ionomer is shown to be substantially enlarged compared to the pristine membrane state. Elemental mapping overlayed with the binary ionic and non-ionic morphology reveals mesoscopic void regions in the degraded material that are depleted of ionomer fluorine and carbon and considered susceptible to micro-crack initiation. A larger, severely degraded void region is also identified which contains evidence of hygrothermal stress induced localized ionomer crazing as a potential nucleation site for macroscopic fracture development. The synergetic effects of chemical and mechanical degradation on the progressive changes in the observed mesoscale morphology are discussed. Cost effectiveness, durability, and efficient performance are the essential requirements to be met for the commercialization of fuel cells. The properties of all key components comprising the fuel cell stack such as bipolar plates, gas diffusion layers, catalyst layers, and ion conducting membrane play a vital role in building the efficient and durable fuel cell system.2 One of the susceptible components responsible for the failure of polymer electrolyte fuel cells (PEFCs) is the ionomer membrane which conducts protons and separates the electrodes. The essential requirements of a standard fuel cell membrane are high proton conduction, good mechanical, chemical, and thermal stabilities, and low gas permeability. The most widely used electrolyte in PEFCs is the perfluorosulfonic acid (PFSA) ionomer membrane. The structure of the PFSA ionomer consists of hydrophobic tetrafluoroethylene main chains with periodic side chains terminated with hydrophilic sulfonic acid groups. When hydrated, the PFSA membrane exhibits a phase segregated network of ionic, water-filled hydrophilic domains which are necessary for enhanced proton conduction and non-ionic backbone dominated hydrophobic domains which are critical for the structural integrity of the material. The morphology of PFSA membranes can be studied using transmission electron microscopy (TEM), which is a direct imaging technique. The dehydrated morphology of a Pb 2+ ion-exchanged membrane viewed under the electron column has revealed phase-separated, dark hydrophilic ion-rich domains and bright polytetrafluoroethylene (PTFE)-like backbone domains.3 Recently, 2D and 3D images of PFSA ionomer were also reported using cry...

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“…When evaluating elastic modulus from a stress-strain curve by extending the hydrated membranes, the cells were deformed by 5% with a speed of 0.0176 m/s along one direction while keeping the cell volume constant under the deformation. To save the calculation cost the deformation rate used here is almost twenty times higher as the deformation rate in the experiment [29]. The general coarse graining molecular dynamics simulator OCTA/COGNAC [30] was used for the calculation.…”

Section: Mechanical Strengthmentioning

confidence: 99%

Modeling and Simulation for Fuel Cell Polymer Electrolyte Membrane

Morohoshi

Hayashi

2013

Polymers

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Abstract:We have established methods to evaluate key properties that are needed to commercialize polyelectrolyte membranes for fuel cell electric vehicles such as water diffusion, gas permeability, and mechanical strength. These methods are based on coarse-graining models. For calculating water diffusion and gas permeability through the membranes, the dissipative particle dynamics-Monte Carlo approach was applied, while mechanical strength of the hydrated membrane was simulated by coarse-grained molecular dynamics. As a result of our systematic search and analysis, we can now grasp the direction necessary to improve water diffusion, gas permeability, and mechanical strength. For water diffusion, a map that reveals the relationship between many kinds of molecular structures and diffusion constants was obtained, in which the direction to enhance the diffusivity by improving membrane structure can be clearly seen. In order to achieve high mechanical strength, the molecular structure should be such that the hydrated membrane contains narrow water channels, but these might decrease the proton conductivity. Therefore, an optimal design of the polymer structure is needed, and the developed models reviewed here make it possible to optimize these molecular structures.

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Viscoelastic properties of Nafion at elevated temperature and humidity

Cited by 131 publications

References 46 publications

Mechanical Characterization of Anion Exchange Membranes by Extensional Rheology under Controlled Hydration

Mechanical Characterization of Anion Exchange Membranes by Extensional Rheology under Controlled Hydration

Progression in the Morphology of Fuel Cell Membranes upon Conjoint Chemical and Mechanical Degradation

Modeling and Simulation for Fuel Cell Polymer Electrolyte Membrane

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