**2.9. Copper and their coatings**

Copper emerges as the only bipolar plate material with the highest possible electrical and thermal conductivity. Studies have shown that in a stimulated PEMFC environment, copper beryllium alloy Ce17200 has a corrosion rate of approximately 0.28 μm year at 70°C.

Materials such as Al, Cu, Sn, Ni, and Ni-phosphorous are very susceptible to electrochemical corrosion in acidic solutions that are typical of PEMFC operating conditions. However, gold shows very high resistance to electrochemical corrosion, in comparison to graphite, the traditional bipolar plate material.

In order for its multifunctional roles to be actualized, its material requirement has to be one of excellent electrical and thermal conductivity, good gas permeability, high mechanical strength, high corrosion resistance, and low weight. Having all these required properties locked up in a single material has ever been a challenge facing the research and development community on bipolar plates. As a result, different materials suited for different applications for bipolar plates such as metal, coated metal, graphite, flexible graphite, carbon–carbon composite, and carbon–polymer composites have been adopted over the years. None of these has been able to fulfill at once all the performance requirements and targets set by the US Department of Energy for fuel cell.
