Flow Field and Current Collector

In large commercial PEMFCs, these flow field plates are made either from graphite/graphite composites or from formed sheet metal. However, forming or even milling solid metal is a little out of reach for low cost hobby applications. Milling graphite composite can be quite messy and the base material is not easy to come by. For our cell, we are not aiming for the high current densities of up to 2 A/cm² of commercial active cells. We want a low cost, easy to manufacture, functional and very robust design. So the material of choice is epoxy-based (FR4) circuit boards with 35 µm copper cladding on one side, available from almost any electronics supplier. As you can imagine, copper is prone to corrosion, or verdigris. This has a detrimental effect on the performance of the fuel cell. The direct effect is that the electrical conductivity of the verdigris is quite poor compared to that of clean copper and therefore significant electrical power losses will occur. The indirect effect is that the copper ions released during the corrosion process poison both the catalyst layer and the ionomer. To prevent this, the copper layer has to be plated with nickel and then gold. While gold is known for its high corrosion resistance and good electrical conductivity, it also tends to sink into the copper. It is therefore necessary to apply a nickel-based barrier layer between the copper and gold layers. Both layers can be applied by electroplating.