THE ROLE OF THE

170 The Role of the Chemist in Automotive Design
Graphite nanofibers are stacked sheets of graphite that can store up to three times
their own weight in hydrogen under pressure at room temperature. A 0.34-nm gap
exists between the graphite layers. Because hydrogen molecules are 0.26 nm, they
fit perfectly into these gaps. At this time, however, much work needs to be done to
perfect storage, manufacture, and control of this technology. The chemist’s role in
this challenge is paramount.
11.6 membrane electrode assembly
Membrane electrode assemblies (MEAs) are typically five-layer structures, as shown
in Figure 10.1. The membrane is located in the center of the assembly and is sandwiched
by two catalyst layers. The membrane thickness can be from 25 to 50 µm
and, as mentioned in Chapter 10, made of perfluorosulfonic acid (Figure 11.3). The
catalyst-coated membranes are platinum on a carbon matrix that is approximately
0.4 mg of platinum per square centimeter; the catalyst layer can be as thick as 25
µm [12]. The carbon/graphite gas diffusion layers are around 300 µm. Opportunities
exist for chemists to improve the design of the gas diffusion layer (GDL) as well as
the membrane materials. The gas diffusion layer’s ability to control its hydrophobic
and hydrophilic characteristics is controlled by chemically treating the material.
Typically, these GDLs are made by paper processing techniques [12].
The cost imperative comes into play greatly with fuel cell membrane assemblies.
It is up to the automotive chemist to design ways to improve the cost structure of
these assemblies. For instance, the perfluorosulfonic membrane (Nafion) by DuPont
is a very expensive component [13]. Other companies, such as Arkema and PolyFuel,
are proposing other films as a cost alternative to the Nafion product [14,15]. The precious
metal catalyst used in membrane assemblies is applied to carbon using batch
methods; if other deposition methods (such as vapor deposition) can be developed,
cost can be reduced [12].
For sealing, there is approximately 1 mile of sealant for an 80-kW fuel-cell stack
[12]. Development of a high-speed application will greatly reduce the cost of manufacturing
these seals. One avenue of cost reduction could be the use of a thin film
manufacturing process, spray coatings, or screen printing [12]. The manufacture of
bipolar plates, which eliminates secondary machining operations, is another cost
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FIgure 11.3 Structure of perfluorosulfonic membrane.
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