Zeolite-Nafion composite membrane

Tricoli V and Nannetti F. Zeolite-Nafion composites as ion conducting membrane materials. Electrochim Acta 2003 48 2625-2633. Libby B, Smyrl WH, and Cussler EL. Polymer-zeolite composite membranes for direct methanol fuel ceUs. AIChE J 2003 49 991-1001. 

Tricoli V, Nannetti F (2003) Zeolite-Nafion composites as ion conducting membrane materials. Electrochim Acta 48 2625-2633... 

Li X, Roberts EPL, Holmes SM, Zholobenko V (2007) Functionalized zeolite A-Nafion composite membranes for direct methanol fuel cells. Solid State Ion 178 1248-1255... 

Fig. 6 Illustration of Nafion-acid functionalized zeolite Beta nanocomposite membranes helping to increase the proton conductivity and decrease the methanol crossover (A) H2O and CH3OH diffusion reduced by zeolite flow resistance (B) sulphonic acid functionalized zeolite nanoparticles increases proton conductivity of composite membranes. (View this art in color at www. dekker. com.)...

Polymer-zeolite composite membranes are also studied in rectors, either as interphase contactors in liquid phase oxidation processes [65] or for improving the properties of Nafion in fuel cells applications [66],... 

Most of the zeolite and montmorillonite fillers used as methanol barrier in Nafion composites decrease the membrane conductivity, except in the case of a sulfonated montmorillonite [67] which exhibit a conductivity increase of 25 % when a composite with Nafion containing 5 wt% of organoclay is prepared. Mesoporous aluminosilicates [73] in concentration as low as 0.5 wt% are reported to increase the conductivity of Nafion by a factor higher than three between 30 °C and 80 °C. 

Supercritical CO2 activation of a Naflon membrane prior to zeolite deposition was used to modify its structure. The resultant Nafion-zeolite composite membranes showed a dramatic decrease in methanol permeability (if the colloidal rather than the suspended Fe-silicalite-1 particles were used for the deposition) and a 19-fold higher selectivity compared with either the composite membranes prepared without previous supercritical treatment or the pure commercial Nafion-115 membrane. The method of the in situ synthesis of a zeolite inside the membrane pores was found to be very effective for preparing the composites, giving a sixfold higher selectivity for the composite manbrane compared with the pure Nation membranes (Gribov et al. 2007). 

Tricoli and Nanetti [17] prepared a novel zeolite-Naflon composite manbrane by embedding zeolite fillers in Nafion. The zeolites used in this study were chabazite and clinoptilolite. The presence of zeolites in the membranes caused notable changes in conductivity, methanol permeability, and selectivity with respect to pure Nafion. In another interesting study, Holmberg et al. synthesized and characterized zeolite-Y nanocrystals for Nafion-zeolite-Y composite proton exchange membranes. The composite membranes were found to be more hydrophilic and proton conductive than the base-unmodified membranes at high temperatures [18]. 

B. Holmberg, H. Wang, J. Norbeck and Y. Yan, Synthesis and characterization of Zeolite Y Nanocrystals for Nafion Zeolite Y composite proton exchange membranes, AIChE, Spring National Meeting, New Orleans, Los Angeles, USA, March 10-14 (2002). 

Polyaniline (PANI) nanocomposite membranes are also prepared by a sol-gel process, embedding silica in the hydrophilic clusters (Nafion) followed by its deposition by redox polymerization [51]. PANI modified the membrane structure and reduced the methanol crossover, while silica Incorporation improved the conductivity and stability. Zeolite has been incorporated as potential filler for PEMs, either by blending or by infiltration in swelled membrane, to reduce the methanol permeability and enhance the thermal stabihty [52,53]. Although the fuel cell performance of these membranes was Inferior compared with pristine Nafion membrane, incorporation of semipermeable particles is an effective method to engineer the transport properties of composite membranes. Chen et al [54] reported nanocomposite membranes by in situ hydrothermal crystallization method, with similar proton conductivity, but low methanol permeability (40% less) in comparison with Nafion membrane. These membranes showed higher OCV (3%) and power density (21%) than Nafion. 

High intensity irradiation of dibenzyl ketone in hexane/isopropanol mixtures yields 1,2-diphenyl ethane and toluene as the sole products. A study of the photochemical behaviour of dibenzyl ketone adsorbed on zeolites has been carried out and the results found to be dependent upon the Sl/Al composition of the zeolite. A laser flash examination of the behaviour of dibenzyl ketone in Nafion membranes has demonstrated that a modest yield of benzyl cations is formed. A study of the physical photochemistry of the ketone (1) has shown that the excited state is a carbonyl localized singlet state. This ultimately decays to afford a naphthalene localized triplet state. Norrish Type I cleavage does occur from the singlet state to afford products derived from the radicals (2) and (3). The authors report also that the 1-naphthyl methyl radical is formed from the triplet state. A study of the modification of the photochemical behaviour of the a-alkyldibenzyl ketones (4) by complexation in... 

Chen et al. [30] reported fabrication of Nafion/zeolite nanocomposite man-branes by hydrothermal growth of acid-functionalized zeolite nanocrystals into commercial Nafion membranes for DMFCs. The presence of zeolite nanocrystals in the composite is confirmed by X-ray diffraction techniques. The tensile strength and water uptake were studied and the performance was compared with that of the... 

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