Nafion properties

The dependence of water uptake from the liquid phase on membrane thermal pretreatment was mentioned in the earliest descriptions of Nafion properties. As Grot et al. have pointed out [57], Nafion membranes take up dramatically more water from liquid water at very high temperatures-up to 100% of the polymer diy weight in the case of Nafion 120 when the membrane is in contact with liquid water at 180 °C. Such expanded ( E-form ) membranes maintain a constant, high water content when in contact with liquid water at temperatures at or below the pretreatment temperature. In contrast, S -form (S for shrunken) membranes are prepared by drying the membranes completely at elevated temperatures. Such membranes imbibe less water than as-received ( normal , N-form) membranes. 

Today, the term solid electrolyte or fast ionic conductor or, sometimes, superionic conductor is used to describe solid materials whose conductivity is wholly due to ionic displacement. Mixed conductors exhibit both ionic and electronic conductivity. Solid electrolytes range from hard, refractory materials, such as 8 mol% Y2C>3-stabilized Zr02(YSZ) or sodium fT-AbCb (NaAluOn), to soft proton-exchange polymeric membranes such as Du Pont s Nafion and include compounds that are stoichiometric (Agl), non-stoichiometric (sodium J3"-A12C>3) or doped (YSZ). The preparation, properties, and some applications of solid electrolytes have been discussed in a number of books2 5 and reviews.6,7 The main commercial application of solid electrolytes is in gas sensors.8,9 Another emerging application is in solid oxide fuel cells.4,5,1, n... 

Klotzbach T, WattM, Ansari Y, Minteer SD. 2006. Effects of hydrophobic modification of chit-osan and Nafion on transport properties, ion-exchange capacities, and enzyme immobilization. J Membrane Sci 282 276-283. 

Nafion, a perfluorinated sulfonated polymer, is a typical example of an ion-exchangeable resin with high promise as a catalyst support. Its properties are significantly different from those of common polymers (stability towards strong bases, and strong oxidizing and reducing acids and thermal stability up to at least 120 °C if the counter ion is a proton, and up to 200-235 °C if it is a... 

A.V. Kashevskii, J. Lei, A.Y. Safronov, and O. Ikeda, Electrocatalytic properties of meso-tetraphenylporphyrin cobalt for nitric oxide oxidation in methanolic solution and in Nafion film. J. 

With the exception of Elder et. al., who used EXAFS to look at redox properties of copper complexes diffused in Nafion film modified electrodes (21), no in-situ studies have been reported on modified electrodes using EXAFS. 

Catalytic properties of the active acid form of the composites obtained in comparison with random copolymers of tetrafluoroethylene and PFAVESF (Nafion-type) were investigated in esterification, oligomerization, and aromatic compounds alkylation reactions. 

The reason for Nafion LB-film fabrication was the wish to obtain the highly ordered systems from perfluorinated ion exchange polymer with multilayered structure, where the ionic layers (conductors) would alternate with fluorocarbon polymer layers (insulators), and to investigate the properties of such films.74 This polymer contains a hydrophobic fluorocarbon polymeric chain and hydrophilic ionic groups, so it is sufficiently amphiphilic it has a comblike structure that makes it a suitable polymer for LB-film deposition. 

The catalyst layer is composed of multiple components, primarily Nafion ion-omer and carbon-supported catalyst particles. The composition governs the macro- and mesostructures of the CL, which in turn have a significant influence on the effective properties of the CL and consequently the overall fuel cell performance. There is a trade-off between ionomer and catalyst loadings for optimum performance. For example, increased Nafion ionomer confenf can improve proton conduction, but the porous channels for reactanf gas fransfer and water removal are reduced. On the other hand, increased Pt loading can enhance the electrochemical reaction rate, and also increase the catalyst layer thickness. 

Porosity and thickness of the porous PTFE substrate have also been found to affect the properties of the reinforced Nafion PEM. Under H2/O2 PC operation at 80°C and a gas pressure of 0.2 MPa, the current densities at 0.6 V were found to increase with increasing pore size 500-850 mA cm for 0.3-0.5 pm pore sizes. Under the same conditions, Nafion 115, Nafion/ PTFE-45 pm, and Nafion/PTFE-25 pm were found to be 800, 800, and 950 mA cm 2, respectively. 

Kim, Y. S., Dong, L., Hickner, M. A., Glass, T. E., Webb, V. and McGrath, J. E. 2003. State of water in disulfonated poly(arylene ether sulfone) copolymers and a perfluorosulfonic acid copolymer (Nafion) and its effect on physical and electrochemical properties. Macromolecules 36 6281-6285. 

Lee, K., Ishihara, A., Mitsushima, S., Kamiya, N. and Ota, K. 2004. Effect of recast temperature on diffusion and dissolution of oxygen and morphological properties in recast Nafion. Journal of the Electrochemical Society 151 A639-A645. Vebrugge, M. R. 1989. Journal of the Electrochemical Society 136 417. 

Bauer, F., Denneler, S. and Wilert-Porada, M. 2005. Influence of temperature and humidity on the mechanical properties of Nafion 117 polymer electrolyte membrane. Journal of Polymer Science Part B Polymer Physics 43 786-795. 

Yang, C., Srinivasan, S., Bocarsly, A. B., Tulyani, S. and Benziger, J. B. 2004. A comparison of physical properties and fuel cell performance of Nafion and zirconium phosphate/Nafion composite membranes. Journal of Membrane Science 237 145-161. 

Figure 6.16 shows a snapshot of the carbon-Nafion-water-solvent (CNWS) blend. The final micro structure was analyzed in terms of density map profiles, RDFs, pore size distributions, and pore shapes. The interaction parameters of the carbon particles were selected to mimic the properties of VULCAN-type C/Pt particles. 

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