Keywords: moulding compounds, environmental degradation, strength, mechanical testing.

The fuel cell is considered to be a promising alternative energy source for the near future. PEM fuel cells are favored especially for use in automobiles due to the high power density, relatively quick start-up, rapid response to varying loads, and low operating temperatures [1,2,3]. A bipolar plate, which is the major component of the fuel cell, is always exposed to moisture during operation, because one of the important functions of the bipolar plate is to facilitate water management within the cell [3]. Various materials are tested for bipolar plates and graphite composite is a promising material for bipolar plates.

In order to use graphite composite materials as a bipolar plate material for PEMFC, the effect of the moisture environment on the mechanical properties of the bipolar plate must be studied. In this study, the bipolar plate samples were constructed and tested to investigate the effect of the moisture and temperature environment on the mechanical properties. Two types of bipolar plate samples, one made of particulate graphite 90%-epoxy 10% composite with woven carbon fabric and the other without carbon fabric, were fabricated. Both types of samples were kept in three different environmental conditions: 1) dry at room temperature 2) immersed in 85°C water for 100 hours and 3) 85°C water for 300 hours. A series of experiments were performed with the samples of the two types: water absorption rate, strength and modulus from the bending and tensile tests.

The results showed that a steep increase in the water absorption rate occurred at the beginning of the test followed by a slow increase afterwards. The total water absorption rate was higher for the samples without fibers since the inserted carbon fibers have a lower porosity and lower water absorption than the particulate graphite - epoxy matrix. The bending strength and modulus were decreased for the two types of specimens. The tensile strength was decreased 35% for the specimen without carbon fiber in the water condition. The tensile strength remained almost the same for the specimens of composite with carbon fiber in the water condition.

1

S. Gottesfeld, T. Zawodzinski, "Polymer electrolyte fuel cells", Advances in Electrochemical Science and Engineering, 5, 195-301, 1997. doi:10.1002/9783527616794.ch4

2

EG & G Services, Fuel cell handbook, Parsons Inc., 2000.

3

V. Mehta, J.S. Cooper, "Review and analysis of PEM fuel cell design and manufacturing", Journal of Power Sources, 114, 32-53, 2003. doi:10.1016/S0378-7753(02)00542-6

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