Protonic conductivities, of composite

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.)...

P. Staiti, M. Minutoli, Influence of composition and acid treatment on proton conduction of composite polybenzimidazole membranes. Journal of Power Sources 94 (2001) 9-13. 

Fig. 7.11 Effect of different HPAs on the proton conductivity of composite membranes as a function of temperature. The sulfonation degree for the SPEEK was 70%. Reprinted with permission from Ref. [24] S. M. J. Zaidi, et al., Proton conducting composite membranes from polyether ether ketone and heteropolyacids for fuel cell applications, J. Membn Scl 173,17-34 (2000). Copyright Elsevier...

E., and Pica, M. (2004) Preparation and proton conductivity of composite ionomeric membranes obtained from gels of amorphous zirconium phosphate sulfophenylenphosphonates in organic solvents./. Mater. Chem., 14,1910-1914. 

Alternatively, electrospun functionalized nanofibers with high proton conductivity could also be incorporated into polymer matrices, in which perfluorosulfonated polymers, such as Nation , were selected as the matrix polymers. With the filled proton-conducting component fibers, the proton conductivity of composite membranes could be greatly enhanced. The relative reports are shown in Table 2.4. 

Proton conductivity of composites, obtained by this method, was measured by impedance spectrometry over frequency range of 1010 Hz. In Figure 6 one can see the dependence of real and imaginary impedance constituents on current frequency as well as Nyquist plot for the sample PC SGS = 50 50 (% v.) at catalyst concentration in SGS of 20% V. 

Proton conductivity of composites, obtained by photoinitiated polymerization, was 10 Sm/cm. This value is by two orders smaller than the values of proton conductivity of nanocomposites on the basis of PVDF. It was also found to be depended on catalyst concentration (Table 4). 

The effect of annealing temperatures (65 - 250 °C) and blend composition of Nafion 117, solution-cast Nafion , poly(vinyl alcohol) (PVA) and Nafion /PVAblend membranes for application to the direct methanol fuel cell is reported in [148], These authors have found that a Nafion /PVAblend membrane at 5 wt% PVA (annealed at 230 °C) show a similar proton conductivity of that found to Nafion 117, but with a three times lower methanol permeability compared to Nafion 117. They also found that for Nafion /PVA (50 wt% PVA) blend membranes, the methanol permeability decreases by approximately one order of magnitude, whilst the proton conductivity remained relatively constant, with increasing annealing temperature. The Nafion /PVA blend membrane at 5 wt% PVA and 230 °C annealing temperature had a similar proton conductivity, but three times lower methanol permeability compared to unannealed Nafion 117 (benchmark in PEM fuel cells). 

Microstructures of CLs vary depending on applicable solvenf, particle sizes of primary carbon powders, ionomer cluster size, temperafure, wetting properties of carbon materials, and composition of the CL ink. These factors determine the complex interactions between Pt/carbon particles, ionomer molecules, and solvent molecules, which control the catalyst layer formation process. The choice of a dispersion medium determines whefher fhe ionomer is to be found in solubilized, colloidal, or precipitated forms. This influences fhe microsfrucfure and fhe pore size disfribution of the CL. i It is vital to understand the conditions under which the ionomer is able to penetrate into primary pores inside agglomerates. Another challenge is to characterize the structure of the ionomer phase in the secondary void spaces between agglomerates and obtain the effective proton conductivity of the layer. 

Figure 18 shows the temperature dependence of the proton conductivity of Nafion and one variety of a sulfonated poly(arylene ether ketone) (unpublished data from the laboratory of one of the authors). The transport properties of the two materials are typical for these classes of membrane materials, based on perfluorinated and hydrocarbon polymers. This is clear from a compilation of Do, Ch 20, and q data for a variety of membrane materials, including Dow membranes of different equivalent weights, Nafion/Si02 composites ° ° (including unpublished data from the laboratory of one of the authors), cross-linked poly ary lenes, and sulfonated poly-(phenoxyphosphazenes) (Figure 19). The data points all center around the curves for Nafion and S—PEK, indicating essentially universal transport behavior for the two classes of membrane materials (only for S—POP are the transport coefficients somewhat lower, suggesting a more reduced percolation in this particular material). This correlation is also true for the electro-osmotic drag coefficients 7 20 and Amcoh...

More recently, H. Iwahara et al. [20] reported that some compounds having the perovskite structure (see Section 2.7.3) become proton conductors if hydrogen is introduced into the crystal, and the solubility of water and proton mobility in perovskites are now actively researched topics [21]. The perovskites which can be tailored to exhibit high protonic conductivity have compositions of the type... 

R.H. He, Q.F. Li, G. Xiao, and N.J. Bjerrum. Proton conductivity of phosphoric acid doped polybenzimidazole and its composites with inorganic proton conductors. Journal of Membrane Science 226, 169-184 2003. 

Matos et al. 60] developed Nafion-titanate nanotube composites as the PEMFC electrolyte operating at elevated temperatures. The addition of 5-15 wt% nanotubes to the ionomer allowed the PEMFC performance essentially to be sustained up to 130 °C. The polarization curves of PEMFCs using composite electrolytes reflected a competing effect between an increase in water uptake due to the extremely large surface area of the nanotubes, and a decrease in the proton conductivity of the composites. 

The membrane shown in Fig. 4.10 was prepared using this three-dimensionally ordered macroporous polyimide obtained according to the above process with AMPS polymer. The proton conductivity and methanol permeability of the composite membrane are summarized in Table 4.2. The proton conductivity of the composite membrane was higher than that of Nafion and the methanol permeability of the composite membrane was slightly lower than that of Nafion . Both tendencies are good for membrane for direct methanol fuel cell. In this way, three-dimensionally ordered macroporous materials are suitable for matrix of soft proton conductive polymer with higher proton conductivity. 

A variety of dopants were evaluated to study their effects on the conductivity of the perovskite material. The measured protonic conductivity of the doped BaCeOs perovskite is compared to standard Y-doped BaCeOs and SrCeOs compositions. As can be seen in Fig. 4.1, the new composition exhibits a conductivity nearly three times that of baseline perovskites. 

Fig. 4.1 Comparison of proton conductivity of modified perovskite to baseline compositions...

Zirconium phosphate, besides the traditional intercalation processes, has been used to produce pillared compounds, such as those involving mixed Fe-Cr oxides [3]. Furthermore, it has been shown [4] that the protonic conductivity of a-zirconium phosphate can be enhanced by the formation of a composite with alumina or silica, an example of synergic cooperation between the oxides and phosphates which are the main classes of compounds highhghted in the book. 

The importance of the choice of casting solvent on membrane properties is also evident in studies of proton conductivity of sulfonated poly-styrene-foZock-(ethylene-co-butylene)-fc/ock-sulfonated polystyrene (SSEBS) (Scheme 2c) membranes prepared from different compositions of mixed casting solvents (MeOH/THF) (Fig. 25). For example, the conductivity of SSEBS membranes possessing a degree of sulfonation (DS) of 27 mol % increases with an increasing fraction of methanol in the solvent mixture. For membranes with a DS of 42 mol %, the proton conductivity increases with concentration of methanol fraction and levels off at higher volume fraction. 

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