Bipolar plate development

Polymer Electrolyte Membrane (PEM) fuel cell bipolar plates, discussion of the difficulties associated with confronting bipolar plate development... 

As can be seen from the illustrations (b) and (d) in Table 6.1 many targets like corrosion resistance electrical conductivity respectively resistivity and flexural strength are easily reached by current composite bipolar plates. Consequently, these requirements are not addressed in composite bipolar plate development (DOE, 2006). However, current composite bipolar plates are too heavy compared to the DOE targets for transportation applications. Therefore, composite bipolar plates in most instances are developed for stationary applications where there is a fewer issue of mass reduction but a target of 40,000 h of lifetime (DOE, 2009) going with composite bipolar plates being insusceptible for corrosion. 

Often the metal bipolar plate develops a passive film layer, which can increase the contact resistance. This resistance can be measured using the contact electric resistance technique (Kim et al., 2002). In this technique, the two sample surfaces are broughf info contact and then separated repeatedly with a chosen frequency as depicfed in Figure 8.15. The passive... 

The bipolar plates are made from either Type 310 or Type 316 stainless steel, which is coated on the fuel side with nickel and aluminized in the seal area around the edge of the plates. Both internally and externally manifolded stacks have been developed. 

Fuel cell technology continues to advance with materials research. The catalyst material has been one of the major expenses in fuel cell design. An anode with about 40% less catalyst has been developed at Forsc-hungszentrum Julich GmbH in Julich, Germany. It has a bipolar plate with areas of different catalytic activity levels. The anode substrate has one phase that does not act as catalyst to methane-vapor reforming reactions, and another phase where it acts as a catalyst. 

There has been an accelerated interest in polymer electrolyte fuel cells within the last few years, which has led to improvements in both cost and performance. Development has reached the point where motive power applications appear achievable at an acceptable cost for commercial markets. Noticeable accomplishments in the technology, which have been published, have been made at Ballard Power Systems. PEFC operation at ambient pressure has been validated for over 25,000 hours with a six-cell stack without forced air flow, humidification, or active cooling (17). Complete fuel cell systems have been demonstrated for a number of transportation applications including public transit buses and passenger automobiles. Recent development has focused on cost reduction and high volume manufacture for the catalyst, membranes, and bipolar plates. 

Several designs for the bipolar plate and ancillary stack components are used by fuel cell developers, and these are described in detail (9, 10, 11, and 12). A typical PAFC stack contains... 

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. 

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... 

Source U.S. Department of Energy. 2007. Technical targets Bipolar plates. Multiyear research, development and demonstration plan, http //wwwl.eere.energy.gov/hydrogenand-fuelcells/mypp/pdfs/fuel cells.pdf (accessed Dec. 2008). 

Progress and Challenges in the Development of Bipolar Plate Materials... 

Section 5.2.2 include composites and metals. From a cost reduction point of view, it is estimated, according to the cost model, that the cost percentage of the plate in a stack can be reduced from -60 to 15-29% if the graphite plate were replaced by the composite plate or metal plate [15]. However, many uncertain factors are involved in the estimation. The progress and major challenges in development of bipolar plates fabricated by these candidate materials will be introduced in the following parf of this section. 

Cunningham, B., and D. G. Baird. 2006. The development of economical bipolar plates for fuel cells. Journal of Materials Chemistry 16 4385-4388. 

In PEMFCs working at low temperatures (20-90 °C), several problems need to be solved before the technological development of fuel cell stacks for different applications. This concerns the properties of the components of the elementary cell, that is, the proton exchange membrane, the electrode (anode and cathode) catalysts, the membrane-electrode assemblies and the bipolar plates [19, 20]. This also concerns the overall system vdth its control and management equipment (circulation of reactants and water, heat exhaust, membrane humidification, etc.). 

PEM fuel cells - continue work on components (electrolyte, electrodes, bipolar plates), systems (modelling and design) and phenomenology (thermohydraulics). Study and development of micro-cells for portable applications. 

Plansee AC is developing chrome-based alloys for SOFC fuel cell bipolar plates deployed in residential applications. 

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. 

An additional component in a fuel cell is the interconnects or bipolar plates. This is a vital component in SOFC development, since it forms the connection between the anode of one cell and the cathode of the next in a stacked arrangement. That is, these components operate as connections between individual fuel cells in a fuel cell stack [128], Then, the interconnects have to be electronically conductive and also possess good impermeability, chemical stability, and good mechanical properties since these components seal the gas chambers for the oxygen and fuel gas feed at either the anode or the cathode [66,137],... 

The reliability/durability of these fuel cells is another major barrier hindering commercialization. Developing durable catalysts, membranes, gas diffusion layers, and bipolar plates are currently the major areas of concentration in the search for technical breakthroughs. 

A special stainless steel was developed in Australia and patented (Jaffray, 1999). Production costs and endurance of the resulting flat plate design (Foger etal, 2000) were improved relative to that of the firm s initial all-ceramic design. The bipolar plates and interconnects were stainless steel. The cell had operational difficulties, and has been discontinued. The firm has just established a UK division, to compete in Europe. 

Alternative materials for bipolar plates include graphite, stainless steels, titanium and aluminium, all with a developed fabrication technique, and coating technique if needed. Major competitors UTC Fuel Cells has an active fuel cell bus programme, but give sparse details of its flow plate and other technology. (See UTC web site.)... 

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