Stainless steel for cost-competitive bipolar plates in PEMFCs

Bipolar plate materials for the PEM fuel cell (also known as the solid polymer fuel cell, SPFC) need to fulfil the following requirements in order to be applicable as an alternative to the presently used graphite: low in cost, easy to machine or to shape, lightweight and low volume, mechanically and sufficiently chemically stable, and with a low contact resistance. Stainless steel is a low-cost material, it is easy to shape and thin sheets can be used, yielding a low volume and weight. Several stainless steels have been tested here for their applicability. The compaction pressure has a significant influence on the contact resistance. The pre-treatment of the surface is another influence; this is a permanent effect. Stainless steel constituents slowly dissolve into the membrane electrode assembly (MEA). It has been found that the anode-side stainless steel flow plate is the main source of the contaminants. Direct contact between the stainless steel and the membrane greatly enhances the contaminant level. By using a proper pretreatment and a coating or gasket to prevent direct contact between the stainless steel and the membrane, we found one alloy that satisfies the requirements for use as a low-cost material for the flow plate of a PEMFC.