Membrane Nafion/PTFE

Yu, T. L., Lin, H., Shen, K., Huang, L., Chang, Y., Jung, G. and Huang, J. C. 2004. Nafion/PTFE composite membranes for fuel cell applications. Journal of Polymer Research Taiwan 11 217-224. 

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. 

Chen LC, Yu TL, Lin HL, Yeh SH (2008) Nafion/PTFE and zirconium phosphate modified Nafion/PTFE composite membranes for direct methanol fuel cells. J Membr Sci 307 10-20... 

Figure 19.9. Polarization curves and the corresponding power density curves of fuel cells with a Pt/C/Nafion-PTFE/C eatalyst cathode and a Pt/C/Nafion membrane-based cathode, respectively. Measured at 80 °C. The hydrogen and air reactant gases were externally humidified at 90 °C and 85 °C, respectively. The flow rates were 50 mL min for hydrogen and 200 mL min for air [49]. (Reprinted from Eleetroehemistry Communications, 8(7), Tian ZQ, Wang XL, Zhang HM, Yi BL, Jiang SP, Microwave-assisted sjmthesis of PTFE/C nanocomposite for polymer electrol)4e fuel cells, 1158-62, 2006, with permission from Elsevier.)...

Table 12.1 Membrane thickness (L), conductivity (tr), and resistance (L/cr) of Nafion and Nafion/PTFE composite membranes...

The main advantage of Nafion/PTFE composite membranes is their low fuel gas crossover and high mechanical strength despite the low thickness L, and thus a low Lla as summarized in Table 12.1. Nafion/PTFE composite membranes can thus be made considerably thinner (<25 pm) than the commercially available Nafion-117,... 

Nafion-115, Nafion-112, and Nafion-212 which have thickness of 175 pm, 125 pm, 50 pm, and 50 pm, respectively. These thiimer composite PEMs contain significantly less amounts of the expensive Nafion resin than the thicker neat Nafion membranes. Thus, another advantage of Nafion/PTFE composite PEMs is the fact that they are inexpensive. Besides porous PTFE films, porous films such as polyethylene (PE) [21, 22] and electro-sptm polymer nanofiber films such as those of poly(vinyhdene fluoride) (PVdF) [23, 24], poly(vinyhdene fluoride-co-hexafluoropropylene) (PVdF-co-HFP) [25], and poly(vinyl alcohol) (PVA) [26-31] have also been used as supporting films for impregnating Nafion ionomer solutions to prepare Nafion/fiber composite PEMs for PEMFC and DMFC applications. 

Table 12.2 Tensile stress of Nation and Nafion/PTFE composite membranes...

Yu TL, Lin HL, Shen KS et al (2004) Nafion/PTFE composite membranes for fuel cell applications. J PolymRes 11 217-224... 

Lin HL, Yu TL, Huang LN (2005) Nafion/PTFE ccun-posite membranes for direct methanol fuel cell applications. J Power Sources 150 11-19... 

Wang L, Xing DM, Liu YH et al (2006) Pt/SiOz catalyst as an addition to Nafion/PTFE self-humidifying composite membrane. J Power Sources 161 61-67... 

Jung GB, Weng FB, Su A et al (2008) Nafion/PTFE/ silicate membranes for high-temperature proton exchange membrane fuel cells. Int J Hydrogtai Energy 33 2413-2417... 

Kawano et al. [8] compared the performance of PTFE fihn at different temperatures with Nafion membrane. As PTFE has almost 100% crystallinity as compared... 

Nafion/PTFE composite membranes were fabricated [17] by impregnation of a porons PI LE film with a solution of Nafion in a 2-propanol/water mixture. After solvent evaporation, the impregnated film was annealed at 120°C for 1 h. The resultant membrane was 20 pm in thickness, with a proton conductivity of 0.033 S cm at 25°C (30% that of Nafion 117), while the methanol flux was 4.43x10 mol cm s (as compared with 1.62x10 mol cm s for Nafion 117 and 6.20x10 mol cm s for Nafion 112). DMEC performance of the composite membrane, measured at 70 C with 2.0 M methanol feed and pure oxygen, was superior to that of both Nafion 112 and 117. 

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