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Lu Z.,University of Delaware | Santare M.H.,University of Delaware | Karlsson A.M.,Cleveland State University | Busby F.C.,Gore Fuel Cell Technologies | Walsh P.,Cleveland State University
Journal of Power Sources | Year: 2014

The electrodes used for Proton Exchange Membrane Fuel Cells (PEMFCs) are typically painted or sprayed onto the membrane during manufacturing, making it difficult to directly characterize their mechanical behavior as a stand-alone material. An experimental-numerical hybrid technique is devised to extract the electrode properties from the experimentally measured properties of Nafion® 211 membrane1 and a membrane electrode assembly (MEA) based on Nafion® 211 membrane at various temperatures, humidities, and strain rates. Within the linear regime, the rule-of-mixtures assuming an iso-strain condition is used to calculate the rate-dependent Young's modulus of the electrodes. Beyond the linear regime, reverse analysis is conducted using finite element models of the MEA to determine the non-linear behavior of the electrodes. The mechanical damage mechanisms that occur in the MEA during tensile loading are also investigated through interrupted tension tests and then incorporated into the finite element models for determining the electrode behavior. The results suggest that the electrodes have similar behavior to Nafion® 211 membrane as functions of strain rate, temperature and humidity, but with lower Young's modulus and proportional limit. © 2013 Elsevier Ltd. All rights reserved. Source

Khattra N.S.,University of Delaware | Santare M.H.,University of Delaware | Karlsson A.M.,Cleveland State University | Schmiedel T.,Gore Fuel Cell Technologies | Busby F.C.,Gore Fuel Cell Technologies
Fuel Cells | Year: 2015

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. Copyright © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Khattra N.S.,University of Delaware | Lu Z.,University of Delaware | Karlsson A.M.,University of Delaware | Santare M.H.,University of Delaware | And 2 more authors.
Journal of Power Sources | Year: 2013

The mechanical response of a composite fuel cell membrane, made from layers of reinforced and unreinforced PFSA material, is investigated via both experimental and numerical means. First, the time-dependent mechanical properties for the reinforced layers are measured for a range of environmental and loading conditions. A three-network, viscoelastic-plastic constitutive model is developed to characterize the mechanical response of this reinforced membrane material. This constitutive model is then used in finite element simulations of a fuel cell unit (consisting of composite membrane, electrodes, gas diffusion layer and bipolar plates) where the effect of relative humidity (RH) cycling on the stress response of the composite membrane is investigated. Using numerical simulations, various layering configurations for the composite membrane and different load cases are studied. The investigation provides insight into the stress response of the membrane and suggests possible configurations that may improve the effective membrane life. © 2012 Published by Elsevier B.V. All rights reserved. Source

Kusoglu A.,University of Delaware | Tang Y.,University of Delaware | Lugo M.,University of Delaware | Karlsson A.M.,University of Delaware | And 3 more authors.
Journal of Power Sources | Year: 2010

The mechanical properties and swelling behavior of perfluorosulfonic acid (PFSA) membranes in liquid water have been investigated using a custom-built, temperature-controlled water bath. Interestingly, the theoretical models of Mooney-Rivlin and Ogden for rubber elasticity are shown to reproduce the major features of the experimentally obtained stress-strain relationships. In addition, stress relaxation of the membrane subjected to a fixed strain at room temperature fits time-dependent constitutive models used to describe nonlinear rubber elasticity. Thus, the experimental results suggest that even though PFSA is not an elastomer, the constitutive models developed for rubber-like behavior can be used for describing the ex situ constitutive response of PFSA membranes with high water content. This response is in contrast to the constitutive behavior of PFSA membranes swollen in water vapor (e.g. humid air and consequently lower water absorption in the membrane) where studies have suggested constitutive behavior corresponding to that of semicrystalline polymers, including distinct features such as a linear regime followed by onset of nonlinearity. © 2009 Elsevier B.V. All rights reserved. Source

Kusoglu A.,University of Delaware | Santare M.H.,University of Delaware | Karlsson A.M.,University of Delaware | Cleghorn S.,Gore Fuel Cell Technologies | Johnson W.B.,Gore Fuel Cell Technologies
Journal of the Electrochemical Society | Year: 2010

The relationship between the mechanical behavior and water transport in the membrane electrode assembly (MEA) is numerically investigated. Swelling plays a key role in the mechanical response of the MEA during fuel cell operation because swelling can be directly linked to the development of stresses. Thus, in the model introduced here, the stresses and the water distribution are coupled. Two membranes are studied: unreinforced perfluorosulfonic acid (PFSA) and an experimental reinforced composite membrane. The results suggest that open-circuit voltage operations lead to a uniform distribution of stresses and plastic deformation, whereas under current-load operation, the stresses and the plastic deformation are generally lower and localized at the cathode side of the MEA. For the experimental reinforced membrane investigated, the in-plane swelling and, consequently, the stresses and plastic deformation are lower than in an unreinforced PFSA membrane. This reduction is a favorable outcome for improving durability. The model also suggests that the mechanical constraints due to the clamping of the cell may limit the swelling of the membrane and consequently change the water distribution. © 2010 The Electrochemical Society. Source

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