Bipolar plates requirements

Thinner, lighter, cheaper bipolar plates required... 

Table 6.1 shows a lack of homogeneity in the definition of bipolar plate requirements. Nevertheless, there has been a differentiation between graphitic and metallic bipolar plates for PEMFC since 2006, as the ways of fabrication and feasible geometries are widely different and stationary, portable and automotive applications are distinct. 

One emerging market for thermally and electrically conductive resins is for bipolar plates for use in fiiel cells. Bipolar plates require high thermal and electrical conductivity. In this study, carbon black and synthetic graphite were added to a liquid crystal polymer and the resulting composites were tested for thermal and electrical conductivity. Single filler composites containing 2.5 to 15 wt% carbon black and 10 to 75 wt% synthetic graphite were tested. 

Functions, Structures, and Performance Requirements of Bipolar Plates... 

Although it is difficult to determine the quantitative requirements of plate and plate materials appropriately for various fuel cells and different applications in a development phase, such a target would be helpful to direct the development effort and make necessary trade-offs. The cascaded performance requirement targets in 2010 and 2015 for bipolar plates of fuel cells in transportation applications were set by the U.S. DoE (Department of Energy) according to functions of the plate mentioned before and overall requirements of performance, reliability, manufacturability, and cost of a stack, as shown in Table 5.1 [7]. The technical target in the DoE s multiyear research, development, and demonstration plan has been popularly and worldwide... 

Thus, the heat release is directly related to the amount of product water. The next consideration is the amount of heat needed to raise fuel cell temperature from, for example, -30 to 0°C (AT = 30 K). The thermal mass of the fuel cell components comes in large part from the bipolar plates (BPPs), neglecting the end plates. With graphite bipolar plates of 1 mm thickness each, and assuming an adiabatic system, the required heat is... 

Fuel cell assembly requires that considerable compression be applied to the stack to ensure tight gas seals and good electrical conductivity at the GDM-bipolar plate interface. This compression leads to reduced porosity, smaller average pore size, and possibly other microstructure changes in the GDM. Since capillary properties... 

For the HTE process, the electrochemical cell consists of a tri-layer ceramic, well known for its brittleness, which limits applied loads. In addition, the relatively low ionic conduction properties of the electrolyte materials (3% yttrium-stabilised zirconia) requires an operating temperature above 700°C to reduce ohmic losses. This creates difficulties for the involved metallic materials, including bipolar plates and seals. 

Carbon meets many of these requirements and has been used by fuel cell makers over many years. Nevertheless, the development of low-cost, nonporous, carbon materials continues to be a challenge and the bipolar plate remains one of the most costly components in a PEMFC system. 

Water management can be most simply achieved by providing the gas feed humidification level required to maintain the conductivity of the fuel-cell membrane and of the ionomers in the catalyst layers. Gas feed humidification has been achieved by a variety of methods including, for example, enthalpy exchangers [6] and porous bipolar plates [62]. The two latter approaches rely on utilization of stack-produced water, thereby eliminating the need of frequent water refill . The system in Fig. 29a, can use a condenser to... 

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