Polymer bipolar plates

Table 9 Opportunities and risks of injection-molded polymer bipolar plates compared to metal plates...

Effect of High Mold temperature and Layout of Gate Position on Conductivity of Composite Polymer Bipolar Plate... 

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. 

Figure 4.1 shows a schematic of a typical polymer electrolyte membrane fuel cell (PEMFC). A typical membrane electrode assembly (MEA) consists of a proton exchange membrane that is in contact with a cathode catalyst layer (CL) on one side and an anode CL on the other side they are sandwiched together between two diffusion layers (DLs). These layers are usually treated (coated) with a hydrophobic agent such as polytetrafluoroethylene (PTFE) in order to improve the water removal within the DL and the fuel cell. It is also common to have a catalyst-backing layer or microporous layer (MPL) between the CL and DL. Usually, bipolar plates with flow field (FF) channels are located on each side of the MFA in order to transport reactants to the... 

Injection molded thermoplastic bipolar plates made of Vectra LCP (liquid crystal polymer) and Fortron PPS fabricated by Ticona Engineering Polymers, (http //www.ticona.com/redesign/ index/markets/innovation/fuel cell.htm Ticona Engineering Polymers. 2008 accessed March 2008.)... 

Cho, E. A., U. S. Jeon, H. Y. Ha, et al. 2004. Gharacteristics of composite bipolar plate for polymer electrolyte membrane fuel cells. Journal of Power Sources 125 178-182. 

Wang, H., and J. A. Turner. 2004. Investigation of a duplex stainless steel as polymer electrolyte membrane fuel cell bipolar plate material. Journal of Power Sources. 128 193-200. 

The electrolyte is a perfluorosulfonic acid ionomer, commercially available under the trade name of Nafion . It is in the form of a membrane about 0.17 mm (0.007 in) thick, and the electrodes are bonded directly onto the surface. The electrodes contain very finely divided platinum or platinum alloys supported on carbon powder or fibers. The bipolar plates are made of graphite-filled polymer or metal. 

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

Bipolar plates are currently made from milled graphite or gold-coated stainless steel. Ongoing research is aiming to replace these materials with polymers or low-cost steel alloys, which will allow the use of low-cost production techniques. Even today, bipolar plates can be produced at 200 /kW, if the production volume... 

Wolf, H. and Willert-Porada, M., Electrically conductive LCP-carbon composite with low carbon content for bipolar plate application in polymer electrolyte membrane fuel cell, J. Power Sources, 153, 41, 2006. 

Wu, M. and Shaw, L.L., A novel concept of carbon-filled polymer blends for applications in PEM fuel cell bipolar plates, Int. J. Hydrogen Energy, 30, 373, 2005. 

Wang, H., Sweikart, M.A., and Turner, J.A., Stainless steel as bipolar plate material for polymer electrolyte membrane fuel cells, J. Power Sources, 115, 243, 2003. 

Silva, R.R et al., Surface conductivity and stability of metallic bipolar plate materials for polymer electrolyte fuel cells, Electrochim. Acta, 51, 3592, 2006. 

The effect of these impacts can be greatly reduced if Pt is recovered and reused, as all heavy metals should be. A strategy for supply of Pt to the fuel cell industry is discussed by Jaffray and Hards (2003). In terms of weight, the stack breakdown on components is shown in Fig. 6.6 for two conventional material choices for the bipolar plates, graphite or aluminium. Recently, bipolar plates made of conducting polymers have been developed (Middleman et al., 2003), with thickness and weight reduction as a consequence. 

Fig. 2. Components of a single polymer electrolyte fuel cell used for laboratory investigations. In a stack, relatively thinner current collectors will become bipolar plates with the flow fields machined on both sides.

Abo El, Enin SA, Abdel-Salam OE, El-Abd H, Amin AM (2008) New electroplated aluminum bipolar plate for PEM fuel cells. J Power Sources 177 131-136 Feng K, Shen Y, Sun H, Liu D, An Q, Cai X, Chu PK (2009) Conductive amorphous carbon-coated 316L stainless steel as bipolar plates in polymer electrolyte membrane fuel cells. Int J Hydrogen Energ 34 6771-6777... 

A component of a fuel cell that consists of a polymer membrane electrolyte coated with (or sandwiched between) positive and negative electrodes and then placed between bipolar plates. 

Thermoplastic carbon composite materials are a favonrable material combination for bipolar plates becanse they can be mannfactnred by the mass production process of injection monlding [102]. Electrical condnctivity of a carbon composite requires a high content of carbon, nsnally a mixtnre of graphite and active coal. The percolation limit of the graphite in the polymer binder has to be exceeded, leading to direct contact between graphite particles. Additionally, a basic condnctivity of the polymer matrix by the smaller active carbon particles is achieved. The injection... 

A polymer electrolyte fuel cell stack with 100 cells and graphite-based bipolar plates is shown in a partly expanded view in Fig. 8.9. 

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