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Research Papers

Crack Formation in Membrane Electrode Assembly Under Static and Cyclic Loadings

[+] Author and Article Information
Masaki Omiya

Department of Mechanical Engineering,
Keio University,
3-14-1, Hiyoshi, Kohoku-ku,
Yokohama, Kanagawa 223-8522, Japan

Toyota Motor Corporation,
Susono,
Shizuoka, Japan

1Corresponding author: oomiya@mech.keio.ac.jp

Contributed by the Advanced Energy Systems Division of ASME for publication in the Journal of Fuel Cell Science and Technology. Manuscript received December 20, 2012; final manuscript received January 18, 2013; published online March 25, 2013. Editor: Nigel M. Sammes.

J. Fuel Cell Sci. Technol 10(2), 021007 (Mar 25, 2013) (8 pages) Paper No: FC-12-1129; doi: 10.1115/1.4023878 History: Received December 20, 2012; Revised January 18, 2013

The mechanical reliability of membrane electrode assemblies (MEAs) in polymer electrolyte fuel cells (PEFCs) is a major concern for fuel cell vehicles. Hygrothermal cyclic conditions induce mechanical stress in MEAs and cracks form under operating conditions. This paper investigates the failure mechanism of MEAs under several mechanical and environmental conditions with the aim of designing durable PEFCs. We performed static tensile tests and low-cycle fatigue tests on MEAs. During the tensile tests, the temperature and humidity of the test chamber were controlled and surface crack formation of MEAs was observed in situ by a video microscope. Low-cycle fatigue tests were performed at ambient conditions and the number of cycles to crack formation was measured. The results reveal that the temperature and the humidity affect the mechanical properties of MEA. Observations of MEAs during tensile tests reveal that cracks form on the surface of catalyst layers immediately after the MEAs yield. These results indicate that reducing the deformation mismatch between the catalyst layer and the proton exchange membrane is important for suppressing crack formation in MEAs. The results of low-cycle fatigue tests reveal that the fatigue strength of a MEA follows the Coffin–Manson law so that fatigue design of MEAs based on the Coffin–Manson law is possible. This result is valuable for designing durable PEFCs.

Copyright © 2013 by ASME
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Figures

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Fig. 1

Experimental equipment. (a) Tensile testing machine, (b) tensile testing machine whose temperature and relative humidity can be controlled, and (c) cross section of experimental chamber.

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Fig. 2

Stress–strain curve of MEA in 25 °C and 50%RH

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Fig. 3

Effect of temperature and relative humidity on Young's modulus

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Fig. 4

Effect of temperature and humidity rate on yield stress

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Fig. 5

Effect of temperature and relative humidity on maximum stress

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Fig. 6

Effect of temperature and relative humidity on rupture strain

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Fig. 7

Surface observation results for ambient conditions (25 °C and 50%RH): (a) ε = 0.07, (b) ε = 0.1, (c) ε = 0.5, and (d) ε = 1.0

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Fig. 8

Relation between stress–strain curve and surface observation results at 25 °C and 50%RH

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Fig. 9

Surface observation results at 25 °C and 80%RH: (a) ε = 0.06, (b) ε = 0.1, (c) ε = 0.3, and (d) ε = 0.7

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Fig. 10

Relation between stress–strain curve and surface observations at 25 °C and 80%RH

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Fig. 11

Surface observation results at 80 °C and 50%RH: (a) ε = 0.03, (b) ε = 0.04, (c) ε = 0.08, and (d) ε = 0.3

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Fig. 12

Relation between stress–strain curve and surface observation results at 80 °C and 50%RH

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Fig. 13

Effect of temperature and relative humidity on crack initiation strain

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Fig. 14

Surface observations during fatigue test for a plastic strain range of 0.03 and a strain rate of 0.0025 s–1 at 25 °C and 50%RH

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Fig. 15

Relation between plastic strain range and number of cycles to crack initiation at 25 °C and 50%RH

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