Nafion 212 membrane

The experimental setup is shown in Figure 9.23. The Pt-black catalyst film also served as the working electrode in a Nafion 117 solid polymer electrolyte cell. The Pt-covered side of the Nafion 117 membrane was exposed to the flowing H2-02 mixture and the other side was in contact with a 0.1 M KOH aqueous solution with an immersed Pt counterelectrode. The Pt catalyst-working electrode potential, Urhe (=Uwr)> was measured with respect to a reversible reference H2 electrode (RHE) via a Luggin capillary in contact with the Pt-free side of the Nafion membrane. 

Du Font s Nafion membranes have been the first truly successful membranes in these applications. They are made of a perfluorinated and sulfonated polyal-kylene ionomer (-CFj- or >CF- throughout). Such a composition leads to... 

Electrolytes for Electrochromic Devices Liquids are generally used as electrolytes in electrochemical research, but they are not well suited for practical devices (such as electrochromic displays, fuel cells, etc.) because of problems with evaporation and leakage. For this reason, solid electrolytes with single-ion conductivity are commonly used (e.g., Nafion membranes with proton conductivity. In contrast to fuel cells in electrochromic devices, current densities are much lower, so for the latter application, a high conductivity value is not a necessary requirement for the electrolyte. 

Dining the last couple of years CdS-containing Nafion membranes have been apphed for the photocleavage of H2S . They are not comparable with the monograin membranes because the CdS particles are at randomly distributed in a rather thick Nafion membrane. This technique is attractive for some applications because the semiconductor particles are immobilized . On the other hand, problems may arise because of diffusion problems in the nafion membrane. Mainly the photoassistol Hj-formation at CdS was investigated in the presence of a Pt-catalyst and with coprecipitated ZnS CdS without a catalyst . 

Systems that contain the photocatalyst as a suspended powder or colloid are not convenient in continuous flow or circulation arrangements in which the photoactive system is held in place and can readily be removed for regeneration. CdS can be produced or immobilized in a Nafion membrane together with finely dispersed platinum... 

Jiang J, Kucernak A. 2004. Investigations of fuel cell reactions at the composite microelectrode solid polymer electrol3de interface. I. Hydrogen oxidation at the nanostructured Pt Nafion membrane interface. J Electroanal Chem 567 123-137. 

Akers NL, Moore CM, Minteer SD. 2005. Development of alcohol/02 biofuel cells using salt-extracted tetrabutylammoiuum bromide/Nafion membranes to immobilize dehydrogenase enzymes. Electrochim Acta 50 2521-2525. 

Run/Nin heteronuclear complexes such as (653), in which a photosensitizer [Ru(bpy)3]2+ or [Ru(phen)3]2+ is covalently attached to the Ni1 cyclam complex, have been synthesized in order to improve the efficiency of electron transfer from the photoexcited photosensitizer to the catalytic site.1 44-1646 However, these complexes did not perform particularly well, either due to unfavorable configuration of the Nin-cyclam subunit and the resulting steric hindrance or due to short lifetime of the excited states of the Ru photosensitizer moieties. A stable catalytic system has been prepared by immobilizing macrocyclic Ni11 complexes and [Ru(bipy)3]2+ in a nafion membrane.164... 

A number of metal porphyrins have been examined as electrocatalysts for H20 reduction to H2. Cobalt complexes of water soluble masri-tetrakis(7V-methylpyridinium-4-yl)porphyrin chloride, meso-tetrakis(4-pyridyl)porphyrin, and mam-tetrakis(A,A,A-trimethylamlinium-4-yl)porphyrin chloride have been shown to catalyze H2 production via controlled potential electrolysis at relatively low overpotential (—0.95 V vs. SCE at Hg pool in 0.1 M in fluoroacetic acid), with nearly 100% current efficiency.12 Since the electrode kinetics appeared to be dominated by porphyrin adsorption at the electrode surface, H2-evolution catalysts have been examined at Co-porphyrin films on electrode surfaces.13,14 These catalytic systems appeared to be limited by slow electron transfer or poor stability.13 However, CoTPP incorporated into a Nafion membrane coated on a Pt electrode shows high activity for H2 production, and the catalysis takes place at the theoretical potential of H+/H2.14... 

Several technical arrangements have been used successfully to immobilize this catalyst on an electrode surface as thin films.80-85 In such arrangements the metal sites in films show a dramatic increase in reactivity and stability toward C02 reduction into CO. Moreover, this kind of modified electrode (for instance [Re(bpy)(CO)3Br] incorporated in Nafion membrane) appeared as a good electrocatalyst in pure aqueous electrolyte.86 However, in such systems both CO and HCOO are also produced, and the total current yield of C02 reduction is lowered by the concurrent H+ reduction into H2. 

Biosensors fabricated on the Nafion and polyion-modified palladium strips are reported by C.-J. Yuan [193], They found that Nafion membrane is capable of eliminating the electrochemical interferences of oxidative species (ascorbic acid and uric acid) on the enzyme electrode. Furthermore, it can restricting the oxidized anionic interferent to adhere on its surface, thereby the fouling of the electrode was avoided. Notably, the stability of the proposed PVA-SbQ/GOD planar electrode is superior to the most commercially available membrane-covered electrodes which have a use life of about ten days only. Compared to the conventional three-dimensional electrodes the proposed planar electrode exhibits a similar... 

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. 

H. Mohan and R. M. Iyer, Photochemical behaviour ofrhodamine 6G in Nafion membrane, J. Chem. Soc. Faraday Trans. 88, 41-45 (1992). 

Platinum chemically deposited on a Nafion membrane was used as a platinum SPE (Solid Polymer Electrolyte) electrode. The electrochemical measurements were performed using the half cell shown in Fig. 2-2. The cell body is made from Teflon (PTFE). The cell is divided into two compartments one for backside gas supply one for the electrolyte. SPE electrodes are placed between them with the deposited side facing the gas compartment. A gold foil with a hole was placed behind the SPE electrode... 

Platinum was deposited on Nafion membrane by the method described earlier. Ibe cyclic voltammogram is shown in Fig. 2-i6 using 3 M H2SO4 as the electrolyte in the solution side of the membrane. The hydrogen adsorption—desorption features are not very well-defined probably because of some impurities. 

Stable performance was demonstrated to 4,000 hours with Nafion membrane cells having 0.13 mg Pt/cm and cell conditions of 2.4/5.1 atmospheres, H2/air, and 80°C (4000 hour performance was 0.5 V at 600 mA/cm ). These results mean that the previous problem of water management is not severe, particularly after thinner membranes of somewhat lower equivalent weight have become available. Some losses may be caused by slow anode catalyst deactivation, but it has been concluded that the platinum catalyst "ripening" phenomenon does not contribute significantly to the long-term performance losses observed in PEFCs (5). 

Nafion absorbs MeOH more selectively than water, and the MeOH diffusion flow is higher than the osmotic water flow in Nafion membranes. Diffusion coefficients of Nafion 117 determined by different techniques have been reported. Ren et al. measured MeOH diffusion coefficients in Nafion 117 membranes exposed to 1.0 M MeOH solutions using pulsed field gradient (PPG) NMR techniques. The MeOH self-diffusion coefficient was 6 x 10 cm S and roughly independent of concentration over the range of 0.5-8.0 M at 30°C. A similar diffusion coefficient was obtained for Nafion 117 at 22°C by Hietala, Maunu, and Sundholm with the same technique. Kauranen and Skou determined the MeOH diffusion coefficient of 4.9 x 10 cm for Nafion... 

Xue, T., Trent, J. S. and Osseo-Asare, K. 1989. Characterization of Nafion membranes by transmission electron microscopy. Journal of Membrane Science 45 261-271. 

Ren, X., Springer, T. E., Zawodzinski, T. A. and Gottesfeld, S. 2000. Methanol transport through Nafion membranes— Electro-osmotic drag effects on potential step measurements. Journal of the Electrochemical Society 147 466-474. 

Ling, J. and Savadogo, O. 2004. Comparison of methanol crossover among four types of Nafion membranes. Journal of the Electrochemical Society 15LA1604-A1610. 

Barragan, V. M., Ruiz-Bauza, C., Villaluenga, J. P. G. and Seoane, B. 2004. Transport of methanol and water through Nafion membranes. Journal of Power Sources 130 22-29. 

Cho, K.-Y, Jung, H.-Y., Choi, N.-S., Sung, S.-H., Park, J.-K., Choi, J.-H. and Sung, Y.-E. 2005. A coated Nafion membrane with a PVdF copolymer/ Nafion blend for direct methanol fuel cells (DMFCs). Solid State Ionics 176 3027-3030. 

Figure 6.4 shows that long-range diff usivities of water in Nafion membranes measured by QENS, Di are equal to self-diff usivities determined by PFG-NMR, Dg, at A > 10. In well-hydrated membranes, the major geometric constraints for water mobility due to the phase-segregated, random network morphology of... 

Elliott et al.i applied classical MD simulations to study the dynamics of small molecules in a model Nafion membrane for A= 1, 3.8, and 9.7. They observed wafer segregafion info "bound" water associated with the sulfonate groups and more loosely attached "free" water. 

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