Bipolar plate trends

The major function of a bipolar plate, or simply called "plate," is to connect each cell electrically and to regulate the reactant gas (typically, hydrogen and air in a hydrogen fuel cell) or reactant liquid (typically, methanol in a DMFC) and liquid or gas coolant supply as well as reaction product removal in desired patterns. This plate must be at least electrically conductive and gas and/or liquid tightened. Considering these important functions and the larger fraction of volume, weight, and cost of the plate in a fuel cell, it is worthwhile to construct this chapter with emphasis on the current status and future trend in bipolar plate research and development, mainly for the plate materials and fabrication process. 

Similarly, research conducted on materials and fabrication methods for GDL and bipolar plates aim to tune their properties in order to improve the fuel cell performance. It is clear that the current trend is the integration of the MEA components in order to improve the architecture of the triple phase boundary region and, consequently, the mass and charge transport. 

Stainless steels, as well as A1-, Ni-, and Ti-based alloys have been studied extensively as possible candidates for bipolar plates. One of the most well-studied materials for bipolar plates is SS 316/316L (16-18% Cr, 10-14% Ni, 2% Mo, rest Fe) other candidates are 310,904L, 446, and 2205. Bare stainless steel plates form a passive 2-A nm chromium oxide surface layer under PEMFC conditiOTs that leads to unacceptably high ICRs. A similar trend is observed for the other alloys and therefore surface modification or surface coatings on selected substrate material has to be considered as a pathway to meet the technical targets of low ICR and high corrosion resistance. 

Trends in short- and lOTiger-term directions for key fuel cell components including electrocatalysts/supports, membranes, and bipolar plates have been elaborated in this section improvement of the performance and durability of these components will directly impact the entire automotive fuel cell system requirements, complexity, and cost. Durable catalysts with enhanced ORR activity, durable membranes that perform at very low humidity and durable bipolar plates that have low contact resistance will not only increase the power density and cost of the fuel cell stack but also simplify and lower/eliminate system component costs of the air compressor, humidification systems, recycle pumps, radiator, start-up/shutdown and freeze-start-related components, etc. A combination of advances in all the fuel cell components discussed above, system simplification, governmental policies that are sensitive to sustainable clean energy, and development of a hydrogen infrastructure will enable achieving the projected technical and cost targets needed for automotive fuel cell commercialization. 

SOFC interconnect could be either ceramic or metals/alloys. Ceramic interconnects are normally used between 800°C and 1000°C, whereas metallic interconnects are preferred for 750°C and below. While doped LaCrOs is used as ceramic interconnects, the Cr-based alloys and ferritic steels are the choice for metallic interconnects. In a recent review article, Sakai et al. (2004) has summarized the trend of research activities in the area of SOFC interconnects (Fig. 21). Very recently possibility of using stainless steel has also been examined by Ishihara et al. (2003) and Bance (2004). For the Siemens-Westinghouse tubular SOFC, the interconnection is deposited in the form of a 85 pm thick, 9 mm wide strip along the air electrode tube length by plasma spraying. On the other hand, bipolar plates having channels on both sides are used for planar geometry. Several materials have been tested for SOFC interconnects, details of which are now available in the literature (Quadakkers 2003). 

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