Modified Nafion membranes

Lead-Ruthenate Pyrochlore Modified Nafion Membrane for Tunable Heterogeneous Catalytic Oxidation... 

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. 

Lead-Ruthenate Pyrochlore Modified Nafion Membrane. 

Several reviews on membranes for DMFC fuel cells have been published in the last decade [1-9], starting with that by Kreuer [1], discussing the differences between Nafion and sulfonated polyether ketone membranes. According to Fig. 6.1, reviews published till 2006 [1 ] cover only one third of the ionomeric membranes currently developed for DAFC. More recent reviews deal with polyimide ionomer membranes [5], composite membranes for high temperature DMFC [6], non-perfluorated sulfonic acid membranes [7], modified Nafion membranes [8], and hybrid membranes [9-11]. 

Si02 surface modified Nafion membranes could be prepared by in situ surfactant-templated sol-gel reaction [38] or by plasma enhanced chemical vapor deposition [45]. Ti02-coated Nafion membranes were prepared by dip coating from a titania sol [85]. 

Organidlnorganic, Grafted, Layer-by-Layer Assembly, and Modified Nafion Membranes... 

Some authors superficially modified Nafion membranes in order to reduce methanol crossover. For instance, hydrocarbon films have been deposited on Nafion membranes by plasma deposition [163], and trilayer membranes were prepared by casting Nafion layers on a central Nafion/PVdF composite layer [164]. Nafion treated with supercritical CO2 seems to increase crystallinity, as well as proton conductivity and DMFC performance [165, 166]. 

Lin Y, Li H, Liu C, Xing W, Ji X (2008) Surface-modified Nafion membranes with mesoporous Si02 layers via a facile dip-coating approach for direct methanol fuel cells. J... 

Barbora L, Singh R, Shroti N, Verma A (2010) Synthesis and characterization of neodymium oxide modified Nafion membrane for direct alcohol fuel cells. Mater Chem Phys 122 211-216... 

Li L, Drillet JF, Macova Z, Dittmeyer R, Jtittner K (2006) Poly(3,4-ethylenedioxy thiophene)-modified Nafion membrane for direct methanol fuel cells. Russ J Electrochem 42 1193-1201... 

Cui ZM, Li NW, Zhou XC, Liu CP, Liao JH, Zhang SB, Xing W (2007) Stuface modified Nafion membrane by casting proton-conducting polyelectrolyte complexes for direct methanol fuel cells. J Power Sources 173 162-165... 

Chapter 6 deals with the description of different membranes used in direct alcohol fuel cells. Firstly, the properties of Nafion and its inorganic and organic composites are analyzed, focused on the proton cmiductivity and alcohol permeability, which determine the alcohol selectivity of the modified Nafion membranes. Then, a number of alternative non-fluorinated proton conducting membranes, including sulfonated polyimides, poly(arylene ether)s, polysulfones, poly(vinyl alcohol), polystyrenes, and acid-doped polybenzimidazoles, are described in relation to their selectivity in comparison to Nafion. The chapter includes a comprehensive summary of the relative selectivity of these membranes and their performance in direct alcohol fuel cells. Anion exchange membranes for alkaline direct alcohol fuel cells are also reviewed. 

Modified Nation membranes, prepared by charging Nafion 117 membranes with different long-chained counterions were used for PV of acetic acid-water mixture (Kusumochyo and Sudoh 1999). It was noticed that the selectivity of the Nafion membranes was enhanced by charging with long-chained counterions. Among the modified Nafion membranes, Naflon(CgHi7)4 was the most suitable membrane with a flux of 0.18 kg/m h and a selectivity of 243 for a feed concentration of 90% acetic acid. 

Yoon et al. used Palladium (Pd) to modify Nafion membranes by coating them with a different thickness of Pd film, using as puttering method (Yoon et al. 2002). The scanning electron microscopy (SEM) micrographs showed that the 10 and 30 nm Pd films were dense and appeared to be well attached to the membrane. However, some cracks were found on the surface of the 100 nm Pd film. It was believed that the cracks were caused by the difference between the Nafion membrane and the Pd film in the expansion that took place when the composite membrane was immersed in water. The Nafion membrane swells more than the Pd film, which eventually develops cracks in the Pd film. Therefore, the sputtering procedures for a membrane thicker than 100 nm apparently need to be improved. From this research, a trade-off between proton conductivity and methanol crossover was noted similar to the results... 

E.A., Ocampo, A.L., Espinosa-Medina, M.A. and Sebastian, P.J. 2003. A modified Nafion membrane with in situ polymerized polypyrrole for the direct methanol fuel cell. LPower Soj. 124 59-64. 

In the Z-scheme MR, one of the key components is the modified Nafion membrane that allows not only the transport of H2 ions, but also the exchange of the electron... 

There was no comprehensive comparison smdy to illustrate the advantages and disadvantages of MR systems with respect to TR. Therefore, as a case study, the generation of H2 and O2 via H2O decomposition reaction was investigated in both conventional Z-scheme reactor and Z-scheme MR systems (Lo et al., 2010). In conventional Z-scheme reactor, H2 and O2 gases were evolved simultaneously in the form of a mixture in a single reactor and in the Z-scheme MR, modified Nafion membrane with Fe -form was used to separate the two compartments of a linked twin reactor and the results are presented in Figure 7.11 and Table 7.4. 

C.F. Martins, L. Neves, I.M. Coelhoso, F. Vaca Chavez, J.G. Crespo, P.J. Sebastiao, Temperature effects on the molecular dynamics of modified NAFION membranes incorporating ionic liquids cations a NMRD study, Fuel Cells 13 (2013) 1166-1176. 

Zeng J, Jiang CP, Wang YH, Chen JW, Zhu SF, Zhao BJ, et al. Studies on polypyrrole modified nafion membrane for vanadium redox flow battery. Electrochem Commun 2008 10 372-5. 

Nafion-112, and Nafion-212, use the thicker membrane Nafion-117 in DMFCs. The use of crosslinked PVA electrospun nano-fiber film supported Nafion composite membranes (Nafion/ PVA-fiber, thickness 50 pm) in DMFCs has been reported to exhibit a much better DMFC performance than Nafion-117 and Nafion/PVA blended PEMs [26-31]. Several researchers blended the Nafion PEMs with low methanol compatible PVA to reduce the methanol crossover in the PEMs [32-35]. However, these modified Nafion membranes had thicknesses greater than 175 pm, which were similar to (or higher than) that of the neat Nafion-117 membrane. Although there was a decrease in the methanol crossover from these Nafion/PVA blended membranes, the proton transfer resistance of these membranes increased, resulting in a lower DMFC performance. The advantage of applying the thin Nafion/PVA-fiber PEMs to the DMFCs is that the methanol crossover can be reduced without increasing the area specific resistance (i.e., Lla) because of low membrane thickness. Table 12.1 summarizes the thickness, proton conductivity, and Lja of the fiber reinforced Nafion composite membranes obtained from literature reports. The mechanical properties of the composite membranes reported in literature are also listed in Table 12.2. 

Z. Floijanczyk, E. Wielgus-Barry and Z. Poltarzewski, Radiation-modified Nafion membranes for methanol fuel cells. Solid State Ionics 145, 119 (2001). 

For the purposes of this discussion, PEMs are classified in modified Nafion , membranes based on functionalized non-fluorinated backbones and acid-base polymer systems. The prior approaches adopted by researchers and some characteristics of the resultant membranes under each classification are presented in this section. 

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