No abstract

No abstract

No abstract

No abstract

The bipolar plate is a multifunctional component of the fuel cell; its primary roles are to evenly distribute reactant gases whilst removing water from the cell. It must also transfer the heat of reaction away from the cell, provide electrical conductivity between adjacent cells and prevent mixing of the fuel and oxidant. An optimized bipolar plate must satisfy a number of materials and construction requirements, have good electrical and thermal conductivity, gas impermeability and corrosion resistance. It should also have minimal volume and weight and be inexpensive. Historically, graphite has been chosen as a compromise between these requirements, it has good electronic conductivity, excellent corrosion resistance and a low density. However, it is expensive, porous in nature, lacks mechanical strength and is not viable for volume production. Two basic types of bipolar plates have emerged as probable replacements for graphite, including composites fabricated from graphite or carbon powder and a polymer resin and metallic. Composite plates are lower cost, lower weight and mechanically stronger than graphite, and they can be fabricated using cost‐effective moulding techniques. Composites are less conductive than graphite, but recent developments have seen conductivities improve to levels approaching that of graphite. Metals, such as stainless steels and titanium, have high mechanical strength and are gas impermeable. Thus, thin bipolar plates can be manufactured using techniques amenable to mass production. The bulk resistivities of most metals are at least an order of magnitude lower than graphite; however, this can be more than offset by contact resistance due to surface oxide layers or corrosion products. The successful utilization of metallic bipolar plates in proton exchange fuel cells depends upon either the identification of metals or alloys with low contact resistance but good corrosion resistance, or the development of low‐cost conductive and protective coatings.