Nafion ionomers

Kamarajugadda and Mazumder [123] used numerical modeling and investigated the effects of ionomer (Nafion) loading, cafalyst (Pt)... 

Figure 14. Distribution of hydrated hydronium complexes for the ionomers, Nafion and SSC PFSA membrane at the intermediate water contents (a) X = 6.4, (b)>. = 9.6.

Industrial production of perfluorinated ionomers, Nafion membranes, and all perfluorinated membranes is costly due to several factors first, the monomers used are expensive to manufacture, since the synthesis requires a large number of steps and the monomers are dangerous to handle. The precautions for safe handling are considerable and costly. Secondly, the PSEPVE monomer is not used for other applications, which limits the volume of production. The most significant cost driver is the scale of production. Today, the volume of the Nafion market for chlor-aUcali electrolysis (150,000 m year ) and fuel cells (150,000 m year ) is about 300,000 m year resulting in a production capacity of 65,000 kg year. When compared to large-scale production of polymers like Nylon (1.2 x 10 m year ), the perfluorinated ionomer membrane is a specialty polymer produced in small volumes. 

At MAS speeds above 5 kHz, two major fluorine-19 resonances can be resolved in the acid form of the perfluorosulfonate ionomer Nafion (DuPont trademark). Xenon-129 NMR is used as an alternative probe of morphologically based sorption environments in Nafion. The xenon-129 spectrum of xenon sorbed into Nafion under a pressure of 12 atm shows two resonances corresponding to two sorption environments. ... 

It should be acknowledged that Risen utilized the concept of the ionic domains in ionomers (Nafion sulfonates, sulfonated linear polystyrene) as microreactors within which transition metal partides can be grown and utilized as catalysts (23-25). Transition metal (e.g. Rh, Ru, Pt, Ag) cations were sorbed by these ionomers from aqueous solutions and preferentially aggregated within the pre-existing clusters of fixed anions. Then, the ionomers were dehydrated, heated and reduced to the metallic state with Hg. Risen discussed the idea of utilizing ionomeric heterophasic morphology to tailor the size and size distributions of the incorporated metal particles. The affected particle sizes in Nafion were observed, by electron microscopy, to be in the range of 25-40 A, which indeed is of the established order of cluster sizes in the pre-modified ionomer. 

As for ASAXS, we are currently using this technique to separate the crystallite and ionic "peak" scattering in the semicrystalline ionomers Nafion and Surlyn. Since these two scattering sources overlap in q-space, it has in the past proved difficult to separate and model these scattering sources, but with ASAXS this task becomes possible. Also, we are investigating the hlgh-q shoulder we have observed in the SAXS patterns of sulfonated polyurethane ionomers[45], which may be evidence of structural order within the ionic aggregates. 

Perfluorosulfonate Ionomers Nafion Dupont Multiple membrane uses... 

Martin et have evaluated the concentration and diffusion coefficients of O2 in commercial perfluorosulfonate ionomer (Nafion ) materials to assess... 

Special post-functionalizable copolymers have also been used to derive acid ionomers by hydrolysis, thus avoiding the difficulties of copolymerizing ionic and nonionic monomers. To this end there are many examples where carboxylic acid polymers are formed by hydrolyzing copolymers containing acrylate esters, acrylonitrile, or maleic anhydride. As described later, a sulfonic acid ionomer, Nafion, is formed by hydrolysis of tetrafluoroethylene copolymerized with a sulfonyl fluoride. 

The sensitivity to hydrolysis is a key issue in many applications. The ester bond in 4GT-PTMO copolymers is sensitive to hydrolysis however, it is fairly protected since most of the ester is contained in a crystalline structure. The addition of a small amount (1-2%) of a hindered aromatic polycarbodiimide substantially increases the lifetime of this material in the presence of hot water or steam [160]. Polyurethanes are susceptible to hydrolytic attack, especially those with polyester soft segments. However, polyester soft segment polyurethanes are generally more resistant to oils, organic solvents, and thermal degradation. lonomers will swell when exposed to water in fact, a commercial hydrated perfluorosulfonic ionomer (Nafion) is used as a membrane separator in chlor-alkali cells. Styrene-diene copolymers and polyolefin TPEs are insensitive to water. 

As discussed in the previous sections, the hydrated cation migration under an applied electric field directly results in the deformation of the material. In fact, when ionomer (Nafion, Flemion) is dry, the interaction between the side chain groups and the cations is very strong and the ionic conductivity of the membrane is very small [Takeji et al. (1982)]. Conversely, when the membrane is hydrated, the interaction between the cations and the anions in the side chains is weakened and it results in bet-... 

Nowadays, the main type of H2 electrodes used in AFCs is a PTFE-bonded electrode with a Pt load of about 0.3 mg cm [12-14]. PAFCs employ H2-difiusion PTFE-bonded electrodes with Pt supported on carbon as catalyst for low loadings of O.l-l.O mg cm [15]. In contrast, PEFCs utilize H2 electrodes in which the catalyst (Pt/C) and the ionomer (Nafion ) are... 

Structures of surfactants suitable for insoluble films containing proteins are shown in Fig. 2. The films can be cast onto solid surfaces from aqueous vesicle dispersions prepared by sonication [24,25] or from solutions in organic solvents [11,19]. Films containing proteins have also been prepared from composites of bilayer-forming ionic surfactants with ionic polymers of opposite charge (Fig. 2). Examples include polystyrene sulfonate [24] or the ionomer Nafion with DDAB (cf. Fig. 2) [27]. 

J.H. Han, K.W. Lee, G.W. Jeon, C.E. Lee, W.K. Park, E.H. Choi, H nuclear magnetic resonance study of hydrated water dynamics in perfluorosulfonic acid ionomer NAFION, Appl. Phys. Lett. 106 (2015) 023104. 

Fig. 11.3 Measured proton conductivity for various materials as a function of temperature. In the temperature regime of interest (80-120° C) for PEM fuel cells, the only presently available conductors are the hydrated ionomers (Nafion , etc.) and display a significant decrease in conductivity as the temperature is increased (due to a decrease in water content)...

In addition to the effect of support on the catalyst dispersion, the interaction with the ionomer (Nafion ) is crucial for the electrochemical performance of the catalyst layer in the fuel cell. Catalyst nanoparticles that are isolated from the ionomer network are electrochemically inactive. Furthermore, the distribution of the ionomer will affect the ohmic resistance and the mass transport of the reactants and/or products in the catalyst layer. Hence, the interface between the catalyst/support/ionomer will influence the overall polarization behavior of the anode. 

The F and NMR resonances of the perfluorinated ionomer, Nafion, are assigned to their corresponding chemical groups using 2D C- F... 

Heat-treated perfluorosulfonic acid ionomer (Nafion N117). Estimated value from the selectivity of CO2 over CH4. f Estimated value from the selectivity of CO2 over CO. 

To illustrate this point, eonsider the membrane plated for 60 minutes. The tubules in this membrane average —9.4 nm in inside radius. At low eoncentrations of salt, the eleetrieal double should be thicker than this tubule radius. Anions are exeluded from the tubes, and ideal cation permselectivity is observed. At high salt concentrations, the electrical double layer is thin relative to the tubule radius. Anions can now enter the tubules, and ideal cation permselectivity is lost (Fig. 11). Finally, the membrane plated for 180 minute shows cation permselectivity almost identical to that of the ionomer Nafion [92], which is a highly cation-permselective polymer used in industrial electrolytic processes [93],... 

In his 1995 patent, Wilson and co-workers desalbed the thin-film technique for fabricating catalyst layers for PEM fuel cells with catalyst loadings <0.35 mg cm. In this method the hydrophobic PTFE employed to bind the catalyst layer is replaced with hydrophilic perfluorosulfonate ionomer (Nafion ). As a result, the binding material in the catalyst layer is composed of the same material as the membrane. Thin-film catalyst layers have been found to operate at almost twice the power density of PTFE-bound catalyst layers. This corresponds to an inaease in active area utilization from 22% to 45.4% when a Nafion -impregnated and PTFE-bound catalyst layer is replaced with a thin-fihn catalyst layer [128]. Moreover, thin-fihn MEA manufacturing techniques are more established and apphcable to stack fabrication [130]. However, utilization of 45% suggests that there is still significant potential for improvement. 

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