Protonic conductivities, of composite membranes

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.)...

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...

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. 

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. 

The composite membranes exhibit a low heteropolyacid extraction after treatment with water at 60 °C for 24 h. The proton conductivity of the membranes increases with increasing content of silicotungstic acid. 

The proton conductivity of SPEEK membrane can be improved by incorporating a fast proton conductor in the polymer matrix as studied by Silva et al. (2005). They utilized zirconium phosphate (ZrPh) pretreated with -propylamine and then with PBI. The pretreatment was to improve the compatibility between ZrPh and SPEEK. Even though the compatibility of the inorganic was good, the proton conductivity and water uptake of the composite membrane were reduced, consequently reducing the methanol permeability. 

The simplest way to improve the proton conductivity of ionomer membranes is to increase lEC, either by using monomers with short side chains or by increasing copolymer composition of sulfonic acid-containing units. The former approach... 

Repeated attempts have been made to modify Nafion-type membranes so as to prevent their drying out at temperatures above 100°C by introducing inorganic materials that have hydrophilic properties. In such composite membranes, the polymer base secures protonic conduction of the membrane, while the inorganic filler raises the membrane s affinity for water. Metal oxides such as Si02, Ti02, and Zr02 can be used. 

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. 

One option is to use Naflon and PTFE composite membrane that is reinforced with microporous medium. Here, the transmission channel is provided by Naflon. This composition can improve the mechanical strength and stability of the membrane. It can also minimize the membrane thickness to save the material cost. At the same time, this structure can improve the distribution of water and the proton conductivity of the membrane [42-44], Gore and Associates Company has developed such product named Gore-Select , The shrinkage of Gore-Select is a quarter of Naflon 117 to better establish dimensional stability. Comparing to Naflon 117, its mechanical strength enhancement is obvious [45-48],... 

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). 

All acidic proton conductors discussed so far in this review have relied on the presence of large amounts of water (A = 10—30) as a mobile phase for the conduction of protons. Current targets for automotive use of hydrogen/air fuel cells are 120 °C and 50% or lower relative humidity. Under these conditions, the conductivity of the membrane decreases due to low water uptake at 50% relative humidity and thus creates large resistive losses in the cell. To meet the needs of advanced fuel cell systems, membranes will have to function without large amounts of absorbed water. Organic—inorganic composites are one preferred approach. ... 

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...

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. 

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