Metallic bipolar plates for proton exchange membrane (PEM) fuel cells

With escalating oil prices and increasing environmental concerns, increasing attention is being paid to the development of proton exchange membrane fuel cells (PEMFCs). A significant part of the PEMFC stack is the bipolar plates (BPs), which account for about 80% of the total weight and 45% of the stack cost. Bipolar plates have traditionally been made of non-porous graphite, which suffers from high cost, heavy weight, low mechanical strength and the need to machine the flow channels. Metallic bipolar plates have many potential advantages, but in the operating environment of the fuel cell they are prone to corrosion or dissolution. To overcome these difficulties, six metals, including SS316L, SS347, SS410, A36 steel, A16061 and Grade 2 Ti, were investigated as potential bipolar plate materials in the simulated PEMFC working conditions. Based on the corrosion and interfacial contact resistance results and price, SS316L was chosen as the candidate bipolar plate material. TiN was coated on SS316L using a Plasma Assisted Physical Vapor Deposition (PAPVD) coating technology and the coatings were about 15μm thick. The TiN-coating increased the polarization resistance by a factor of 30 and reduced the corrosion current density by a factor of 40. Polypyrrole, a conductive polymer, has been coated on SS316L using electrochemical methods. Potentiodynamic tests showed that the corrosion current density is decreased by a factor of 17 and polarization resistance was increased by a factor of 10.5 by coating with polypyrrole. The nucleation and growth of polypyrrole can be divided into three stages. The first stage is the incubation period. The second stage is a combination of instantaneous nucleation with 2-D (IN2D) or 3-D growth (IN3D). The third stage is a combination of instantaneous nucleation or progressive nucleation and 3D growth (IN3D and PN3D). A Taguchi DOE method was then used to optimize the polypyrrole-coating parameters for SS316L for metallic bipolar plate application. In order to further improve the characteristics of polypyrrole coating, an Au interlayer was coated on SS316L before coating polypyrrole