Abstract
The bipolar plate is of critical importance to the efficient and long lasting operation of a polymer electrolyte fuel cell (PEMFC) stack. With advances in membrane electrode assembly (MEA) design greater attention has been focused on the bipolar plate and the important role it plays in performance and durability. Although carbon composite plates are a likely candidate for the mass introduction of fuel cells, it is metallic plates made from thin strip materials (typically 0.2 mm thick stainless strip) which could deliver significant advantages in terms of part cost, electrical performance and size. However, there are some disadvantages. Firstly, interfacial stability of the metal interconnect is difficult to achieve leading to migration of ions into the MEA and also an increase in contact resistance. Secondly, and the issue addressed here, is the difficultly and cost in developing new plate designs when there are very significant tooling costs associated with manufacture. The use of selective laser melting (SLM: an additive manufacturing technique) was explored to produce metallic bipolar plates for PEMFC as a route to inexpensively test several plate designs without committing to tooling. Crucial to this was proving that, electrically, bipolar plates fabricated by SLM behave similarly to those produced by conventional manufacturing techniques. This research presents the development of a small stack to compare the short term performance of metallic (316L stainless steel) plates made by machining against those made by SLM. Polarisation curves and impedance experiments were conducted. These demonstrate that the cell performance was unaffected by the manufacturing method used and that the pure resistive content of the impedance spectra, a proportion of which could be attributed to contact resistance between the MEA and plate, was very similar. It is concluded that additive manufacturing could be a very useful tool to aid the rapid development of metallic bipolar plate designs. However, when making direct comparisons with very space efficient designs, some challenges exist in the generation of very thin planar forms which would be most representative of sheet metal parts.
