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Research Papers

In Situ Observation of Deformation Behavior of Membrane Electrode Assembly Under Humidity Cycles

[+] Author and Article Information
Yusuke Kai, Yuki Kitayama

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

Masaki Omiya

Department of Mechanical Engineering,
Keio University,
3-14-1 Hiyoshi, Kohoku-ku, Yokohama,
Kanagawa 223-8522, Japan
e-mail: oomiya@mech.keio.ac.jp

Tomoaki Uchiyama, Hideyuki Kumei

Toyota Motor Corporation,
Mishuku 1200,
Susono, Shizuoka 410-1193, Japan

1Corresponding author.

Contributed by the Advanced Energy Systems Division of ASME for publication in the JOURNAL OF FUEL CELL SCIENCE AND TECHNOLOGY. Manuscript received March 28, 2014; final manuscript received May 23, 2014; published online August 26, 2014. Editor: Nigel M. Sammes.

J. Fuel Cell Sci. Technol 11(5), 051006 (Aug 26, 2014) (7 pages) Paper No: FC-14-1034; doi: 10.1115/1.4028155 History: Received March 28, 2014; Revised May 23, 2014

The mechanical reliability of the membrane electrode assembly (MEA) in polymer electrolyte fuel cells (PEFCs) is a major concern with respect to fuel cell vehicles. When PEFCs generate power, water is generated. The proton exchange membrane (PEM) swells in wet conditions and shrinks in dry conditions. These cyclic conditions induce mechanical stress in the MEA, and cracks are formed. Failure of the MEA can result in leaking of fuel gases and reduced output power. Therefore, it is necessary to determine the mechanical reliability of the MEA under various mechanical and environmental conditions. The purpose of the present paper is to observe the deformation behavior of the MEA under humidity cycles. We have developed a device in which the constrained condition of the GDL is modeled by carbon bars of 100 to 500 μm in diameter. The carbon bars are placed side by side and are pressed against the MEA. The device was placed in a temperature and humidity controlled chamber, and humidity cycles were applied to the specimen. During the tests, cross sections of the specimen were observed by microscope, and the strain was calculated based on the curvature of the specimen. The temperature in the test chamber was varied from 25 to 80 °C, and the relative humidity was varied from 50 to 100%RH, and the wet condition was also investigated. The results revealed that the MEA deformed significantly by swelling and residual deformation was observed under the dry condition, even for one humidity cycle. The crack formation criteria for one humidity cycle corresponded approximately with those of the static tensile tests. The results of the humidity cycle tests followed Coffin–Manson law, and the number of cycles until crack formation corresponded approximately with the results of the mechanical fatigue tests. These results will be valuable in the critical design of durable PEFCs.

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Figures

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Fig. 1

(a) Experimental apparatus used in the humidity cycle tests. (b) Cross-sectional view of the experimental chamber.

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Fig. 2

Clearance between the carbon fibers of the GDL

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Fig. 3

(a) Profile of relative humidity for the humidity change tests. (b) Profile of relative humidity for the humidity cycle tests.

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Fig. 4

Results of the surface observation of the MEA constrained by 500-μm-diameter carbon bars obtained in a humidity change test at humidities ranging from 50%RH to the wet condition

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Fig. 5

Depths of surface cracks on MEA constrained by carbon bars obtained in a humidity change test at humidities ranging from 50%RH to the wet condition

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Fig. 6

Cross-sectional observation of the MEA constrained by 500-μm-diameter carbon bars at 25 °C (a) at 80%RH, (b) at 100%RH, (c) under the wet condition, and (d) after the test

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Fig. 7

Results for strain obtained in the humidity change tests at (a) 25 °C, (b) 40 °C, (c) 60 °C, and (d) 80 °C

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Fig. 8

Surface observation of the MEA during humidity cycle tests using 300-μm-diameter carbon bars at 25 °C (a) after three cycles and (b) after 10 cycles

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Fig. 9

Cross section observation of the MEA constrained by 300-μm-diameter carbon bars at 25 °C, (a) under the wet condition after the first cycle, (b) at the 50%RH condition after the first cycle, and (c) under the wet condition after the second cycle

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Fig. 10

Strain history of the MEA constrained by 300-μm-diameter carbon bars at 25 °C

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Fig. 11

Results of mechanical low-cycle fatigue tests of the MEA and humidity cycle tests

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Fig. 12

Buckling deformation of the constrained MEA due to humidity change

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Fig. 13

Critical distances for the clearance between carbon fibers at (a) 25 °C, (b) 40 °C, (c) 60 °C, and (d) 80 °C

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