Application of coupled thermal analysis techniques to thermodynamic studies of water interactions with a compressible ionic polymer matrix

Escoubes, M.; Pinéri, M.; Robens, E.

doi:10.1016/0040-6031(84)87283-4

Cited by 24 publications

(30 citation statements)

References 27 publications

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“…[8] suggests that for a highly swollen membrane ( w   0.25), the swelling pressure is between 20 and 25 MPa, which is higher than the cell assembly pressures (1 to 3 MPa), but within the same order of magnitude with the measured values in this work and in the literature. [21][22][23] The consistency between the measured and calculated pressure values also lend credence to the modeling approach taken.…”

Section: Resultsmentioning

confidence: 99%

“…[18][19][20] There are a limited number of studies focused on measuring the swelling pressure in the membrane using custom-made fixtures and reported pressures between 30-100 MPa. [21][22][23] Moreover, except for a few studies investigating the constraints in PEFCs, 1,3,24 mathematical models generally assume that membranes are unconstrained (although with a given thickness, i.e., swelling is ignored). In fact, there has been only minimal research into swelling of constrained polymers in general with notable exceptions of gels and elastomers, for which Flory-Rehner theory 25,26 is commonly employed to develop models.…”

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confidence: 99%

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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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Section: Resultsmentioning

confidence: 99%

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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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“…For example, clamping pressure was shown to change the cell polarization and power density [51]. The change in the water-uptake behavior of the membrane with compression has been observed experimentally using in situ neutron imaging of an operating fuel cell [52,53] and in compression tests [46,54,55], and predicted using a multi-parameter model based on nanostructural deformation [46]. The model determined the compression effect on membrane's water content using changes in chemical-potential equilibrium by accounting for microscopic deformation of the matrix surrounding the swollen water (hydropilic) domains [46].…”

Section: Introductionmentioning

confidence: 98%

Effect of compression on PFSA-ionomer morphology and predicted conductivity changes

Kusoglu

Hexemer

Jiang

et al. 2012

Journal of Membrane Science

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“…(2,14) subject to the boundary condition in Eq. (15) and to continuity with the coating model in Section 2.1.4; Eq.…”

Section: Original Research Papermentioning

confidence: 99%

“…A mole of water absorbed in the membrane occupies the same volume as a mole of liquid water and each mole of membrane can accommodate 22 moles of water. This causes the membrane to swell up to 70% larger than its dry volume [1][2][3][4][5][6][7][8][9][10]. This swelling makes the application of wet coatings to Nafion, even by hand, difficult ( Figure 1) [6,[11][12][13][14].…”

Section: Introductionmentioning

confidence: 99%

Dynamic Thermal, Transport and Mechanical Model of Fuel Cell Membrane Swelling

2011

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When polymer electrolyte membrane materials are exposed to liquid water, they swell and distort. This frustrates the process of depositing liquid catalyst ink directly onto the membrane. We present a model predicting the transient compositional, thermal, and mechanical response of a membrane undergoing changes in water content. The model describes coupled heat and mass transfer and solid mechanics and is capable of describing the large changes in size and shape exhibited by a swelling membrane. Simulation results are presented for sorption and desorption and for the process of drying a saturated piece of membrane with an aqueous coating applied. We suggest that the well‐established discrepancy in the rate of sorption and desorption may be partially due to pressure‐driven diffusion effects absent in other models but present in ours. We also demonstrate that the model can represent the transient curling behavior of a membrane undergoing nonuniform changes in water content. The model will later be used to predict manufacturing defects caused by swelling‐induced wrinkling.

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Application of coupled thermal analysis techniques to thermodynamic studies of water interactions with a compressible ionic polymer matrix

Cited by 24 publications

References 27 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

Effect of compression on PFSA-ionomer morphology and predicted conductivity changes

Dynamic Thermal, Transport and Mechanical Model of Fuel Cell Membrane Swelling

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