Proton conductivity results

Though no spectroscopic data are available for Ca(OH)2 and Al(OH)3, the larger activation energy for the former and the smaller activation 

If the conductivity mechanism proposed here is correct, the number of excess protons that carry the current in region II must be very small. It would therefore be of interest to determine independently the charge carrier concentration. 

The appearance of the large inverted TSDp maximum at 115-120K coincides with region II, i.e. the temperature interval of positive U(T values where H charge carriers dominate. Its maximum intensity is reached at the same temperature at which the proton conductivity passes through its maximum in Fig. 9.5. To determine the concentration of excess protons [H ] contributing to the 115-120 K inverted maximum we apply Fermi-Dirac statistics 

for the intrinsic case, we obtain an expression for the charge carrier densities in terms of (N N ) and T 

Assuming that the protonic space charges which give rise to the negative TSDp maxima are thermally generated, the transport of the charge carriers as a function of time t along the spatial coordinate x leads to the 

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As mentioned in Sect. 6.3.6., PVA-based membranes were the focus of abundant studies during the last years, and the review by Maiti et al. [180] summarized the conductivity and methanol permeability of most of the PVA-based membranes, whose preparation procedures are described in detail in that work. Figure 6.28 shows the relative selectivity plot for PVA-based membranes. Pure PVA have a low relative methanol permeability but also low proton conductivity resulting in / r 1,... 

Carbon nanotubes (CNTs) have been added to a polymeric matrix to improve their mechanical and other properties [69]. The use of CNTs in PEM must be carried out with caution because the well-known high electrical conductivity may cause short circuiting in proton exchange membrane fuel cells. The jt-n interaction between PBI and the side walls of CNT makes these two different materials compatible. Despite CNT-PBI composite membranes have shown enhancement in mechanical strength, the proton conductivity resulted in some cases compromised [70, 71]. Hence, different authors functionalized the CNTS in order to increase both the proton conductivity and the mechanical properties for hydrogen fed PBI-based HT-PEMFC [72, 73]. In this context,... 

On the other hand, for a predominantly hydrophobic Pt/C surface, depicted on the right-hand side of Figure 3.41, hydrophobic ionomer backbones will be preferentially oriented toward the Pt/C surface. This unfavorable scenario exerts a negative impact on (i) proton conductivity resulting from the relatively low density of sulfonic acid head groups at the ionomer surface, (ii) electrocatalytic activity due to the low concentration of protons in the dehydrated region between Pt surface... 

Perovskite oxides offer in almost all respects a wide variety of properties because of the structure s ability to host varying cations, substitutions, nonstoichiometry, and defects of many kinds. Proton conduction, resulting from oxide ability to dissolve protons from water vapor or hydrogen, is no exception Some perovskites contain virtually no protons at all and are thus barriers to protons, hydrogen, and water vapor. Other perovskites are dominated by proton defects to high temperatures and are predominantly proton conductors. 

HC1 in ethyl alcohol causes a marked drop in the electrical conductivity, which is ascribed to the partial suppression of proton jumps resulting from the capture of protons from the (C2H5OH2)+ ions, thus ... 

But when the contents of Nafion ionomer was increased from 30 to 45 % to find out the better electrode structures, the Pt-Ru/SRaw, which had showed the lowest single cell performance, became the best electro-catalyst. By this result one can conclude that as long as the structure of the electrode can be optimized for the each of new electro-catalysts, the active metal size is a more important design parameter rather than inter-metal distances. Furthermore, when the electro-catalysts are designed, the principal parameters should be determined in the consideration of the electrode structures which affect on the electron conduction, gas permeability, proton conductivity, and so on. 

Thus, measurement of the total conductivity together with the cell voltage allows the transport numbers of the ions to be determined (Fig. 8.17). The results show that at lower temperatures proton conductivity is of greatest importance, at middle temperatures oxygen ion conductivity becomes dominant, and at high temperatures the material is predominantly a hole conductor. Between these temperatures, at approximately 350°C the solid is a mixed H+ and O2- conductor while at approximately 650°C it is a mixed hole and O2- conductor. 

Alberti et al. investigated the influence of relative humidity on proton conductivity and the thermal stability of Nafion 117 and compared their results with data they obtained for sulfonated poly(ether ether ketone) membranes over the broad, high temperature range 80—160 °C and RHs from 35 to 100%. The authors constructed a special cell used in conjunction with an impedance analyzer for this purpose. Data were collected at high temperatures within the context of reducing Pt catalyst CO poison-... 

The last comprehensive review covering proton conductivity and proton conducting materials was written by one of the authors (dating back to 1996) since then, there have been several other review articles of similar scope (e.g., see Colomban ). There are also many reviews available on separator materials used for fuel cells (see articles in refs 3 and 4 and references therein, recent review-type articles, " and a literature survey ), which, more or less, address all properties that are relevant for their functioning in a fuel cell. The transport properties are usually described in these articles however, the treatments are frequently restricted to macroscopic approaches and handwaving arguments about the transport mechanisms. The purpose of the present review is to combine a few recently published results in the context of a discussion of transport phenomena in proton-conducting separator materials, which have some relevance in fuel cell applications (for a more complete list of the comprehensive literature in the field, the interested reader is referred to the aforementioned references). 

Hence, the two main foci of this review are (i) the current understanding of the underlying elementary processes and (ii) a phenomenological description of the resulting macroscopic transport phenomena. Because the first aspect comprises proton conduction mechanisms other than the mechanisms of parasitic transport , this review may also be considered an... 

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