Nafion membranes basis

While detection of cations via porphyrin-ba.sed materials has been explored less than anion sensing, the ability of a porphyrin to coordinate different metals and the unique spectral signatures that result form the basis for metal ion detection. Use of free-base porphyrins in polymer matrices has allowed for the detection of heavy metal ions by Ache et Immobilization of 5,10,15,20-tetrakis(4-N-methylpyridyOporphyrin on Nafion membranes pennitted detection of cadmium and mercury in solution with detection limits of 5 X 10 M and 2 x 10 M, respectively over a 20-minute measuring period. The method is subject to interferences from other metal ions, but the researchers were able to detect several ions simultaneously using pattern-recognition techniques such as principal component analysis. Sol-gel films doped with 5,l0,l5,20-tetra(p-sulfonatophenyDporphyrin have also been used by Ache and coworkers for the fluorimetric determination of mercury in solution, with a detection limit of approximately 7 X 10... 

In principle, using the DPD results [20], it was possible to mimic SAXS and SANS experiments to discriminate the structural models used for interpretation of the experimental data [20]. Also, Hyodo [21] proposed a hierarchical procedure for calculating the electronic states of a hydronium ion in a hydrated Nafion membrane via the mesoscopic structure predicted by DPD [20]. A mixed basis function method was introduced for electronic state calculations in inhomogeneous fields as a combination of Gaussian basis functions and shape functions of the finite element method for expressing electronic wave functions. 

Concentration Method. The concentration procedure that was developed and evaluated was a RO-Donnan dialysis system (4). The initial objective during method development was to conduct membranescreening tests to evaluate the suitability of various RO and ion-exchange membranes. The four membranes considered for final evaluation on the basis of solute rejection, chlorine stability, and artifact production were the cellulose acetate and FT-30 (Film Tec) RO membranes, the Nafion cation-exchange membrane, and the ION AC MA 3475 anion-exchange membrane. 

As a base of proton conducting membrane polyvinyl alcohol (PVS) and phenolsulfonic acid (PSA) was synthesized [9]. Membrane is rendered on a surface of a catalytic layer and dries up at room temperature. As shown in [9], at ratio PVS PSA=4 1 the membrane surpasses widely used in PEMFC membranes on the Nafion basis. Besides, experimental data testily that the solution can successfully be used as a connecting element for the anode and the cathode bonding at FC assembly. 

Experiments were carried out with Ionac MC 3470 to determine the self-diffusion coefficient values for H+ and Al + in the coupled transport. Data points were used from the experiment involving 2N acid sweep solution in Figure 34.24b, presented later. These values formed the basis for aluminum transport rate or flux (7ai) calculation at different time intervals. The equilibrium data generated in Figure 34.20b were used in conjunction with Equation 34.25 to determine the interdiffusion coefficient values. Local equilibrium was assumed at the membrane-water interface. Eigure 34.24a shows computed Dai,h values for this membrane. When compared with Dai,h values for Nafion 117, it was noticed that the drop in interdiffusion coefficient values was not so steep, indicative of slow kinetics. The model discussed earlier was applied to determine the self-diffusion coefficient values of aluminum and hydrogen ions in Ionac MC 3470 membrane. A notable point was that the osmosis effect was not taken into account in this case, as no significant osmosis was observed in a separate experiment. 

Differences in conductivity data of modified perfluorosulfonate membranes can be related to structural differences on the basis of the pore structure models. Smaller equivalent weights (e.g., for Nafion 105, Dow, Membrane C), that is, higher specific ion content, lead to superior performance compared to Nafion 117 due to narrower psds and, thus, more homogeneous water distributions. 

In the previous section it was suggested that the parent polymer structure considerably influence the physical properties of the derived polysulfonates, imparting to them some of the mechanical and thermal properties of the precursors. This trend is particularly evident in the case of the perfluorinated hydrocarbon polymers. Polymers of this kind, such as e.g., poly(tetrafluoroethylene) (PTFE) are exceptional in their inertness to offensive environment, solvent resistance and high-temperature stability. These considerations led in the sixties to the development of unique sulfonic-acid derivatives of fluorocarbon copolymers by the DuPont Company. While several compositions were disclosed in the patent literature51, the preferred composition, which is the basis for the commercial Nafion ion-exchange membrane, is a copolymer of tetrafluoroethylene with a perfluorinated vinyl ether/sulfonyl fluoride52 ... 

Various simulation techniques, as applied to PEFCs, differing in the degree of coarseness and the basie equations solved have been reviewed [10-14]. In contrast to these reviews, in which the transport phenomena in ionomer membranes are discussed in detail, we will consider the problems related to the modeling of Nafion morphology, with the emphasis on the role of water content. 

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