Proton conduction behavior

The built-in and operation stresses are the consequences of the large swelling and shrinkage of the ionomer membrane when it uptakes and loses water. This is frequently referred to as dimensional instability in the literature. Water in the PFSA membrane is an essential ingredient of its proton conduction behavior. Water affects the morphology13,14 of the ionic clusters (at nanoscale) which... 

Figure 2.6 (a) Arrhenius-type, temperature-dependant proton conductivity behavior of PAQSH-XX membranes, (b) Proton conductivity of PAQSH-XX membranes as a function of lEC. Reproduced with permission from Ref. [ 156],... 

Tanaka R, Yamamoto H, Shono A et al (20(X)) Proton conducting behavior in non-crosslinked and... 

Tanaka, R., Yamamoto, H., Shono, A., Kubo, K., and Sakurai, M., 2000, Proton conducting behavior in non-crosslinked and crossUnked polyethylenimine with excess phosphoric acid, Electrochim. Acta 45 1385-1389. 

Ceramic powders of BaCeo.9Yo.1O2.95 (BCYIO) have been prepared by the sol-gel method [115]. Barium and yttriimi acetate and cerium nitrate were used as ceramic precursors in a water solution. The reaction process studied by DTA-TG and XRD showed that calcination of the precursor powder at r>1000°C produces a single perovskite phase. The densification behavior of green compacts studied by constant heating rate dilatometry revealed that the shrinkage rate was maximal at 1430 °C. Sintered densities higher than 95% of the theoretical one were thus obtained below 1500 °C. The bulk and additional blocking effects were characterized by impedance spectroscopy in an wet atmosphere between 150 and 600 °C. Proton conduction behavior was clearly identified. 

Acid-base and blend membranes are alternative candidates for hybrid/composite polyelectrolytes. " Fully aromatic polymers are currently widely used polymer blenders except for Nation itself. The purpose for acid-base blending is to find an optimal compromise between enhancement of proton conductivity by sulfonation and improvement of thermal and morphological stability by composition. In blend composite membranes, the majority partner should ensure good proton-conducting behavior, and the minority partner should improve the mechanical properties and... 

Figure 15. Extent of methanol crossover through different ETFE proton-conducting membranes. Comparison with the behavior ofNafion 117 ( ).

A number of factors must be taken into account when the diagrammatic representation of mixed proton conductivity is attempted. The behavior of the solid depends upon the temperature, the dopant concentration, the partial pressure of oxygen, and the partial pressure of hydrogen or water vapor. Schematic representation of defect concentrations in mixed proton conductors on a Brouwer diagram therefore requires a four-dimensional depiction. A three-dimensional plot can be constructed if two variables, often temperature and dopant concentration, are fixed (Fig. 8.18a). It is often clearer to use two-dimensional sections of such a plot, constructed with three variables fixed (Fig. 8.18h-8.18<7). 

The study of the dynamical behavior of water molecules and protons as a function of the state of hydration is of great importance for understanding the mechanisms of proton and water transport and their coupling. Such studies can rationalize the influence of the random self-organized polymer morphology and water uptake on effective physicochemical properties (i.e., proton conductivity, water permeation rates, and electro-osmotic drag coefficients). 

Cation—sulfonate interactions, as well as proton mobility, are also expressed in the electrical conductance behavior of these membranes. Many studies of this property have been reported, and there is no attempt in this review to cite and describe them all. Rather, a few notable examples are chosen. Most testing is done using alternating current of low voltage to avoid complications in the form of chemical... 

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...

Development of compact fuel cells, created by combining proton conductive perovskite-type oxide ceramics with metal-hydride materials, has been already proposed [1], Our group expects that the compact fuel cells can be utilized under radiation environments such as fission and fusion reactors or cosmic [2], Therefore, it is very important to understand behaviors of electron and proton conductions under radiation environments. 

Figure 2 Properties in polyphosphazenes are determined hy (1) the backbone bonds that control the inherent flexibility of the polymer via their influence on bond torsional freedom, and also provide photo-and thermo-oxidative stahihty (2) the side groups control polymer solubility, reactivity, thermal stability, crystallinity, cross-linking, and (indirectly) polymer flexibility (3) free volume between the side groups affects polymer motion, solvent penetration, membrane behavior, and density (4) functional groups (usually introduced hy secondary reactions) affect soluhihty, biological behavior, proton conduction, cross-hnking, and many other properties...

In the present stndy, as part of an ongoing program to develop new electrolytes with fnrther higher proton conductivity at lower operating temperatnre near room temperature and nnderstand the proton behavior on the decomposed chains in the polymer, garmna-ray irradiation to the membranes was examined in air at room temperatnre and the radiation effects on the protonic condnction process were investigated by proton conductivity, optical absorption and ion-exchange capacity measnrements. 

At the same time it is interesting to understand why the intracellular 756 cm 1 mode influences the proton conductivity. As we mentioned above, the polarized optical 99-cm 1 mode activates the proton mobility in the range Tc < T < To, where Tc= 120K and 7o = 213 K. However, the intracellular 756-cm 1 mode is not polarized nevertheless, it is responsible for the proton mobility for T > To. With T > Tc = 120 K, these two modes demonstrate an anomalous temperature behavior and the intracellular mode begins to intensify [47], It is the intensification of the cellular mode with T, which leads to its strong coupling with charge carriers in the crystal studied. A detailed theory of the mixture of the two modes is posed in Appendix D. 

The effect of "residual water" on either protein stability or enzyme activity continues to be a topic of great interest. For example, several properties of lysozyme (e.g., heat capacity, diamagnetic susceptibility (Hageman, 1988), and dielectric behavior (Bone and Pethig, 1985 Bone, 1996)) show an inflection point at the hydration limit. Detailed studies on the direct current protonic conductivity of lysozyme powders at various levels of hydration have suggested that the onset of hydration-induced protonic conduction (and quite possibly for the onset of enzymatic activity) occurs at the hydration limit. It was hypothesized that this threshold corresponds to the formation of a percolation network of absorbed water molecules on the surface of the protein (Careri et al., 1988). More recently. Smith et al., (2002) have shown that, beyond the hydration limit, the heat of interaction of water with the amorphous solid approaches the heat of condensation of water, as we have shown to be the case for amorphous sugars. 

---