Conductivity membrane swelling

Earlier, Gavach et al. studied the superselectivity of Nafion 125 sulfonate membranes in contact with aqueous NaCl solutions using the methods of zero-current membrane potential, electrolyte desorption kinetics into pure water, co-ion and counterion selfdiffusion fluxes, co-ion fluxes under a constant current, and membrane electrical conductance. Superselectivity refers to a condition where anion transport is very small relative to cation transport. The exclusion of the anions in these systems is much greater than that as predicted by simple Donnan equilibrium theory that involves the equality of chemical potentials of cations and anions across the membrane—electrolyte interface as well as the principle of electroneutrality. The results showed the importance of membrane swelling there is a loss of superselectivity, in that there is a decrease in the counterion/co-ion mobility, with greater swelling. 

Several models of the random pore space and its evolution upon membrane swelling are suggested in Refs. 39, 40 to bridge the gap between the conductivity of a single pore and the conductance of a membrane. Combined with experimental data on psds they reveal the features that cause good or bad membrane performance. 

Relation between Membrane Swelling and Conductivity. The membrane conductivity of Nafion in various solvents has been measured in a very recent study (12). For high < 1 solvents, the transport of ions, like Li+, in the Nafion membrane is related to the swelling of the membrane in the solvent, as shown in Figure 7. In contrast to this, for solvents of less than 12 Hb,... 

Bacterial cellulose has several unique properties that potentially make it a valuable material for the development of PEM fuel cells (Reference 1) (1) it is an inexpensive and non-toxic natural resource (2) it has good chemical and mechanical stability (3) it is very hydrophilic and (4) it doesn t re-swell after drying. Additionally, its thermal stability and gas crossover characteristics are superior to Nation 117 , a material currently widely used as a proton conductive membrane in PEM fuel cells. 

Saarinen V, Kreuer KD, Schuster M, Merkle R, Maier J (2007) On the swelling properties of proton conducting membranes for direct methanol fuel cells. Solid State Itm 178 533-537... 

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... 

Blending of sulfonated PEEK with other polymers sueh as PPSU in sulfonated form or with inorganie eomponent such as SiCU and inorganic oxides like zirconia, as well as with solid heteropolyacids as HPA, TPA and Na-TPA or with BPO4, it is possible significantly to improve the membrane swelling behaviours, the mechanical properties and the proton conductivity. Other efforts have been earried to reaeh the same results following different... 

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