Nafion has been the workhorse PEM of choice for PEFCs and DMFCs for the past 20 years. Its structure is shown in Figure 9.4. While well-suited for use in PEFCs run on hydrogen and oxygen, Nafion is not well-suited for use in DMFCs in large part due to methanol permeability. Efforts to develop a more appropriate PEM for use in DMFCs continues. The ideal membrane is impermeable to methanol, allows facile proton conduction, has good ionic conductivity, can operate over a wide variety of temperatures (e. g., >100°C), and is mechanically and chemically robust. Efforts to develop PEMs appropriate for DMFCs fall roughly into two categories, one focused with developing entirely new PEM materials, the other focused on tailoring the properties of Nafion [24,55,56].

[(CF2CF2)n-CF2CF-]

(OCF2CF-)m ocf2cf2so3h

CF3

FIGURE 9.4 Chemical structure of Nafion where m is usually 1 and n varies from 6 to 14.