Nafion®-bonded

Then apply a Nafion-bonded hydrophilic ink onto the top surface of the above hydrophobic layer as a hydrophilic layer, and at the same time can also ionize the hydrophobic layer. 

Wei ZD, Chan SH, Li LL, Cai HF, Xia ZT, Sun CX. Electrodepositing Pt on a Nafion-bonded carbon electrode as a catalyzed electrode for oxygen reduction reaction. Electrochim Acta 2005 50(11) 2279-87. 

Aside from being sprayed on the GDL, the catalyst ink can also be applied to the membrane to make a Nafion-bonded hydrophilic CL. To efficiently extend the three-phase reaction zone and reduce the Pt loading, Wilson et al. [37,39,41] developed a thin-fihn electrode using Nafion ionomer as the bonder. Their preparation process uses a decal method, the details of which are as follows [39] ... 

The result is a thin-film, Nafion -bonded hydrophilic electrode in which the catalyst and ionomer are thoroughly mixed, but which lacks the passage for gas and water transport because it has no hydrophobic agent. So, this electrode is usually made very thin (5-10 pm) to avoid water flooding Fig. 2.14 shows the fuel cell performance of a thin-film electrode prepared by the above method. It can seen that the electrode exhibited a good performance with a Pt loading of just 0.13 mg cm. ... 

In addition to the electrode-bonded and Nafion-bonded catalyst layers, which involve only surface reaction, a design with Nafion impregnated into the electrode catalyst layer or impregnation of electrode within a thin layer of electrolyte membrane is also used to increase the active surface area as shown in Figure 9.7. 

The working electrode was modified by pipetting a controlled amount of BiFePc/MWCNT and Nafion ink onto the electrode surface, resulting in a formation of a thin layer comprising of Nafion bonded catalyst (BiFePc/MWCNT/Nafion ). The pipetted solution is then prepared by ultrasoni-cally mixing the BiFePc/MWCNT in a Nafion ionomer solution. 

Interfacial degradation is especially common in DMFC systems operating with membranes that are alternatives to Nafion . The main reason for the enhanced probability of an interfacial failure in such systems is poor compatibility between the non-Nafion polymer in the membrane and Nafion -bonded electrodes (Kim et al. 2004). 

The electrolyte is a perfluorosulfonic acid ionomer, commercially available under the trade name of Nafion . It is in the form of a membrane about 0.17 mm (0.007 in) thick, and the electrodes are bonded directly onto the surface. The elec trodes contain veiy finely divided platinum or platinum alloys supported on carbon powder or fibers. The bipolar plates are made of graphite or metal. 

The hydration of triple bonds is generally carried out with mercuric ion salts (often the sulfate or acetate) as catalysts. Mercuric oxide in the presence of an acid is also a common reagent. Since the addition follows Markovnikov s rule, only acetylene gives an aldehyde. All other triple-bond compounds give ketones (for a method of reversing the orientation for terminal alkynes, see 15-16). With allqmes of the form RC=CH methyl ketones are formed almost exclusively, but with RC=CR both possible products are usually obtained. The reaction can be conveniently carried out with a catalyst prepared by impregnating mercuric oxide onto Nafion-H (a superacidic perfluorinated resinsulfonic acid). ... 

Implementation of Pt/C catalysts in PEFC technology using recast Nafion as a proton conducting and bonding agent [Raistrick, 1986 Wilson and Gottesfeld, 1992]. 

An alternative approach to the use of partially fluorinated systems to reduce the cost of fluorinated PEMs has been developed by DeSimone et al. a perfluo-rinated vinyl ether is copolymerized with a hydrocarbon monomer (styrene), sulfonated, and then subsequently fluorinated to replace existing C-H bonds with C-E bonds (Eigure 3.18). Thus yields the perfluorinated, cross-linked sul-fonyl fluoride membrane that can then be hydrolyzed to give the PEM (7). Because the membranes are cross-linked, considerably higher acid contents (up to 1.82 meq/g) are possible for these materials in comparison to Nafion, leading also to higher proton conductivity values. 

The situation for hydrated Nafion in the acid form, or as containing aqueous acids or strong bases, is more complex because protons and defect protons (i.e., OH ions), migrate according to a somewhat different mechanism. Proton transfer in either case occurs throughout and between clusters of hydrogen bonded water molecules to a degree that depends on the relative water content. 

Ostrowska and Narebska noted an infrared continuous absorption in hydrated acid form Nafion 120 membranes that began at 3400 cm and extended toward low wavenumbers. This feature was not present in dry membranes and, based on the work of Zundel et al., was proposed to be due to the existence of Hs02 and Hg04 groups, in which there are easily polarizable hydrogen bonds. This paper by Ostrowska and Narebska is also useful, as it contains a number of band assignments for Nafion. 

At first thought, it might be considered that the steric restrictions posed by the large fluorine atoms would cause conformational rigidity due to restricted bond rotations. Hsu, however, showed that the conformations of the TFE chains in the crystalline regions in Nafion are in fact dynamic in that they can undergo helix reversals that is, the handedness of the helix is easily reversed.These helix reversals are also seen in PTFE.2 o This disorder phenomenon causes considerable conformational entropy and is... 

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