Nafion membranes, operational stability

Finally, to favor the commercial issue of DMFC, new low cost components have to be developed, including catalysts with a lower amount of PGM or even with no noble metal, and high-temperature-resistant membranes of lower cost than sulfonated perfiuorinated membrane (Nafion ) and of higher protonic conductivity and stability to operate the DMFC at higher temperatures (150-200 °C) which may increase the power density through thermal activation of the reaction kinetics. 

Nafion membrane is a nonreinforced film based on Nafion ionomers in acid (H" ") form. Under PEM fuel cell operating conditions, the Nafion membrane is the most practical solid electrolyte due to its unique structure, excellent thermal and mechanical stability, and high proton conductivity (but it is also an isolator for electronic conduction). According to the cluster network model [63-66] of Nafion membrane, Nafion contains some sulfonic ion clusters with a diameter of approximately 4nm. The clusters are equally distributed within a continuous fluorocarbon lattice, and are interconnected by narrow channels with a diameter of about 1 nm this provides passages for the transport of protons. Figure 1.8 shows this cluster network model. Proton... 

The most commercially successful are membranes Nafion (Du Pont, USA). Nafion is perfluorosulfonic ionomer with high proton conductivity and chemical and mechanical stability [6]. However, limited operation temperature, low water uptake, and high cost are disadvantages of the perfluorosulfonic polymer. 

V. Ramani, H.R. Kunz, and J.M. Fenton, Stabilized Heteropolyacid/Nafion Composite Membranes for Elevated Temperature/Low Relative Humidity PEFC Operation, Electrochimica Acta, 50, 1181-87 (2005). 

Ramani, V. Kunz, H. R. Fenton, J. M., Stabilized heteropolyacid/Nafion [trademark] composite membranes for elevated temperature/low relative humidity PEFC operation. Electrochimica Acta 2005, 50, (5), 1181-1187. 

The membrane in a membrane fuel cell fulfils several important functions as stated in the introduction. Nafion was the first commercially available membrane, which lead to a breakthrough in fuel cell technology. Today, various companies are engaged in membrane development especially for this purpose, aiming at improved material properties. The goals are less sensitivity towards elevated temperature and dry operation, better chemical and mechanical stability and reduced methanol crossover for DMFC operation. A significant improvement of the mechanical stability was achieved by incorporation of a PTFE porous sheet as mechanical support for the membrane material [13,14]. 

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