Nafion membranes structure

Hora, C.J. Maloney, D.E. "Nafion Membranes Structured for High Efficiency Chlor-Alkali Cells", presented at the 152nd National Meeting of The Electrochemical Society, Inc., Atlanta, Ga., October 10-14, 1977. 

Repeated membrane failures during the early part of the 12-kW plant 500-hour DMMP run prevented effective control of water balance and levels of silver and organic material in the catholyte system. After laboratory-scale testing from October 11 to October 21,2001, AEA concluded that the failures resulted from foaming or pockmarks in the lattice structure of the PTFE support in the Nafion membrane and that the pockmarks formed only if the membrane came into contact with the cathode. 

The concepts and techniques discussed by Cirkel and Okada are relevant with a view toward modifying the structure of solution cast Nafion membranes by manipulating counterion type, solvent, temperature, and other variables. 

SECM is a useful electrochemical technique for imaging the smface topographical structure at solid/liquid interfaces. " " Briefly, the electrochemical system consists of a 10 pm Pt-ultramicroelectrode (UME) with Ag/AgCl (3 M KCl) as the reference and Pt as the coimter electrode. The unmodified- and Pyc modified-Nafion membranes (side-1) are carefully moimted on a homemade plastic plate on the bottom of the SECM cell. 

Ab initio methods provide elegant solutions to the problem of simulating proton diffusion and conduction with the vehicular and Grotthuss mechanism. Modeling of water and representative Nation clusters has been readily performed. Notable findings include the formation of a defect structure in the ordered liquid water cluster. The activation energy for the defect formation is similar to that for conduction of proton in Nafion membrane. Classical MD methods can only account for physical diffusion of proton but can create very realistic model... 

Figure 3.3.5 (A) Chemical structure of sulfonated perfluorinated polyethylene (Nafion ). (B) Schematic illustration of the microscopic structure of hydrated Nafion membrane perfluorinated polyethylene backbone chains form spherical hydrophobic clusters. Sulfonic end groups interface with water-filled channels and mediate the migration and diffusion of protons. The channels are filled with water and hydronium ions. Figure adapted from [4].

In a H2/air fuel cell, the protons produced at the anode side need to be transferred to the cathode side to react with 02. This requires a proton transport electrolyte. Nafion membranes, composed of a perfluorosulfonated polymer, are the most commonly used polymer electrolyte membranes to conduct protons. The structure of the Nafion membrane is shown in Figure 1.5. Nafion can take on a... 

As shown in Figure 1.6, the optimized cathode and anode structures in PEMFCs include carbon paper or carbon cloth coated with a carbon-PTFE (polytetrafluoroethylene) sub-layer (or diffusion layer) and a catalyst layer containing carbon-supported catalyst and Nafion ionomer. The two electrodes are hot pressed with the Nafion membrane in between to form a membrane electrode assembly (MEA), which is the core of the PEMFC. Other methods, such as catalyst coated membranes, have also been used in the preparation of MEAs. 

Fig. 22. Chemical structure of Nafion11 and schematic illustration for microphase separation in Nafion " membrane.

Spectroscopic studies of the structure of Nafion membranes suggest the presence of nodules of diameter 1-10 run (the lighter parts in Fig. 3.43). The nodules are fairly regularly distributed and have been explained as spherical... 

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