Transport numbers of cations

The rate of product formation can be predicted from a knowledge of the conductivity and transport numbers of cations in the product barrier phase and appropriate thermodynamic data. This interpretation is based on the Wagner model (Sect. 2.3). 

Table 2.2 Transport numbers of cations at various concentrations (mol dm-3). Relative accuracy 0.02 per cent. (According to B. E. 

The conductivity of many metal modified systems is reportedly enhanced due to various factors such as charge transfer between metal ions and the electron-rich heteroatoms, elimination of impurities, and changes in the transport number of cations and anions due to environmental changes in the solid electrolytes. Even interesting cases have been reported where a polymer film can reach the electronically conducting metallic level by cis-trans isomerization. 

Transport Numbers of Cations in Aqueous Solutions at 298 K in 0.1 NSoiutions... 

Figure 3.5 Effect of membrane composition on electrical conductivity and transport number of cation exchange membrane prepared by the paste method. (O, O) transport number ( , ) specific conductivity. DVB divinylbenzene St styrene PVC poly(vinyl chloride). Composition DVB/(St + DVB) — 0.1 (by weight) numbers in the figure are DOP/PVC (DOP dioctyl phthalate -additives) (by weight). The copolymer membrane is sulfonated with concentrated sulfuric acid.

In general, it is found that the transport number of electrons, or electronic defects, is close to unity, compared with which the transport numbers of cations or anions are negligibly small. In these cases. Equations (3.44) and (3.45) reduce to Equations (3.46) and (3.47), respectively ... 

In writing equation (8.18) we assumed that only cations migrate. However, in many oxides, anions also contribute to the ionic flux. Sometimes, they even dominate the growth mechanism. Table 8.8 shows the transport numbers of cations, t+, and anions, t, for a number of oxides. The transport number indicates the fraction of the ionic current carried by a given species. For binary oxides that contain only one type of cations and anions 1+ + = 1. 

Table 8.8 Transport number of cations and anions for different oxides [8].

For example, in a solution with solvent S in which one electrolyte solute A is dissolved, the transport numbers of cation t+ and of anion r are given by... 

They were not been able to quantitatively determine the solvent contribution as it is not possible to evaluate the individual amount of each species involved in the charge compensation process. However, with some hypotheses (e.g. assuming that solvent molecules are associated with the hydration layer of the cations, fs = hfc) they were able to extract information on the transport number of cations with potential and on the relation between the participation of solvent and the oxidation state of the polymer matrix. 

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