Membrane PFSA/PTFE

One activity at DuPont s Fuel Cells Business Center is the development of a thinner membrane with sufficient mechanical stabdity. Thinner membranes translate into higher current density, which in turn means a higher electrical efficiency. The tradeoff is a less mechanically robust membrane. Nafion membranes are nonreinforced films based on Nafion resin, a PFSA/PTFE copolymer in the acid (H+) form. DuPont is especially marketing Nafion PFSA NR-111 and NR-112 membranes as nonreinforced dispersion-cast films for that purpose. These membranes are dehvered as a composite with the membrane positioned between a backing film and a coversheet. This composite is wound on a 6 in. i.d plastic core, with the backing film facing out, as shown in Figure 27.21. 

Figure 10.4 Scanning electron microscopy images of cross-sections ofthe PFSA/PTFE composite membrane.

Recently, DuPont has introduced a new membrane that is an improvement in comparison to earlier versions NR-111, NR-112, and NR-211. DuPont Nation XL membrane is an extended-lifetime reinforced membrane based on chemically stabilized PFSA/PTFE copolymer in the acid (H-f) form. The reinforcement improves the handling of the membrane and its physical properties. When the reinforcement is combined with the chemically stabilized polymer, the membrane... 

PFSA lonomer in Expanded Porous PTFE, Gore-Select Membranes.786... 

PFSA lonomer and PTFE Reinforcement at Asahi Kasei Aciplex Membranes.794... 

PFSA membranes possess high proton conductivity in the range of 0.1 S cm" at 80°C and good chemical as well as mechanical stability. The superior stability of Nafion is a consequence of the PTFE-based structure that is chemically... 

The molecular structure of a conventional polymer used for a PFSA membrane is shown in Fig. 1. Membranes registered as Nafion (DuPont), Flemion , (Asahi Glass), and Aciplex (Asahi Chemical) have been commercialized for brine electrolysis and they are used in the form of alkali metal salt. Figure 4 shows a schematic illustration of a membrane for chlor-alkali electrolysis. The PFSA layer is laminated with a thin perfluorocarboxylic acid layer, and both sides of the composite membrane are hydrophilized to avoid the sticking of evolved hydrogen and chlorine. The membrane is reinforced with PTFE cloth. The technology was applied to PEFC membranes with thickness of over 50 xm [14]. 

The membrane development for PEFCs comprises many steps, as shown in Fig. 7. The multiple steps in monomer synthesis for PFSA preparation is often said to be one of the major factors in the high cost of the PFSA membranes. In fact, PTFE and ethylene-tetrafiuoroethylene copolymer (ETFE), whose synthetic scheme is very simple, are available at comparably low price. As a matter of fact, a considerably large quantity of the ETFE sheet was used... 

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