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Research Papers

The Effect of Mechanical Fatigue on the Lifetimes of Membrane Electrode Assemblies

[+] Author and Article Information
Michael Pestrak

Department of Macromolecular Science and Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061

Yongqiang Li, Scott W. Case, David A. Dillard

Department of Engineering Science and Mechanics, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061

Michael W. Ellis

Department of Mechanical Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061

Yeh-Hung Lai, Craig S. Gittleman

Fuel Cell Research Laboratories, GM R&D General Motors Corporation, 10 Carriage Street, Honeoye Falls, NY 14472

J. Fuel Cell Sci. Technol 7(4), 041009 (Apr 07, 2010) (10 pages) doi:10.1115/1.4000629 History: Received July 10, 2008; Revised August 25, 2009; Published April 07, 2010; Online April 07, 2010

Long-term durability of the membrane electrode assembly (MEA) in proton exchange membrane (PEM) fuel cells is one of the major technological barriers to the commercialization of fuel cell vehicles. The cracks in the electrode layers of the MEA, referred to as mud-cracks, are potential contributors to the failure in the PEM. To investigate how these mud-cracks affect the mechanical durability of the MEA, pressure-loaded blister tests are performed at 90°C to determine the biaxial fatigue strength of Gore-Primea® series 57 MEA. In these volume-controlled tests, leaking rate is determined as a function of fatigue cycles. The failure is defined to occur when the leaking rate exceeds a specified threshold. Postmortem characterization using bubble point testing and field emission scanning electron microscopy (FESEM) was conducted to provide visual documentation of leaking failure sites. The analysis of the experimental leaking data indicates that the MEA has much shorter lifetimes at the same nominal stress levels than membrane samples without the electrode layers. FESEM photomicrographs of leaking locations identified via the bubble point testing show cracks in the membrane that are concentrated within the mud-cracks of the electrode layer. These two pieces of information indicate that the mud-cracks within the electrode layers contribute to the leaking failures of the MEA assembly. For the fuel cell industry, this study suggests there is an opportunity to reduce the likelihood of membrane pinhole failures by reducing the size and occurrence of the mud-cracks formed during the MEA processing or by increasing the fatigue resistance (including the notch sensitivity) of the membrane material within the MEA.

Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Cross section of mechanical fatigue apparatus

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Figure 2

View of plate and block of mechanical fatigue apparatus

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Figure 3

Diagram of bubble point testing apparatus

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Figure 4

Gore MEA at 90°C under 20-4 s cycling in the blister fixture

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Figure 5

Results from four Gore MEA samples tested at 90°C under 20-4 s cycling in the blister fixture

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Figure 6

Results from four Gore MEA samples tested at 90°C under 4-20 s cycling in the blister fixture

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Figure 7

Leaking rate model validation plot

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Figure 8

The reciprocal relaxation time results for the 20-4 s cycling data of Fig. 5

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Figure 9

The reciprocal relaxation time results for the 4-20 s cycling data of Fig. 6

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Figure 10

Comparison between Gore PEM and MEA at 90°C under various cycling

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Figure 11

Comparison between Gore PEM and MEA at 90°C under various cycling

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Figure 12

Comparison of various cycling ratios using leaking rate failure criteria

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Figure 13

Plot of the times that the various duty cycles

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Figure 14

A characteristic bubble point test image of MEA at 90°C

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Figure 15

A characteristic bubble point test image of MEA at 90°C

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Figure 16

A characteristic bubble point test image of MEA at 90°C

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Figure 17

Image of mud-crack in as-received MEA sample

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Figure 18

Image of damage within mud-crack in MEA sample tested at 90°C under 20-20 s cycling

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Figure 19

Image of damage within mud-crack in MEA sample tested at 90°C under 20-20 s cycling

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