Preparation, electrical, mechanical and thermal properties of composite bipolar plate for a fuel cell

A novel composite bipolar plate for a polymer electrolyte fuel cell has been prepared by a bulk-moulding compound (BMC) process. The electrical resistance of the composite material decreases from 20 000 to 5.8 mOmega as the graphite content is increased from 60 to 80 wt.%. Meanwhile, the electrical resistance of composite increases from 6.5 to 25.2 mOmega as the graphite size is decreased from 1000 to 177 mum to less than 53 mum. The thermal decomposition of 5% weight loss of composite bipolar plate is higher than 250degreesC. The oxygen permeability of the composite bipolar plate is 5.82 x 10(-8) (cm(3)/cm(2) s) when the graphite content is 75 wt.%, and increases from 6.76 x 10(-8) to 3.28 x 10(-5) (cm(3)/cm(2) s) as the graphite size is longer or smaller than 75 wt.%. The flexibility of the plate decreases with increasing graphite content. The flexural strength of the plate decreases with decrease in graphite size from 31.25 MPa (1000-177 mum) to 15.96 MPa (53 mum). The flexural modulus decreases with decrease of graphite size from 6923 MPa (1000-177 mum) to 4585 MPa (53 mum). The corrosion currents for plates containing different graphite contents and graphite sizes are all less than 10(-7) A cm(-2). The composite bipolar plates with different graphite contents and graphite sizes meet UL-94V-0 tests, and the limiting oxygen contents are higher than 50. Testing show that composite bipolar plates with optimum composition are very similar to that of the graphite bipolar plate. (C) 2004 Elsevier B.V. All rights reserved.