Ionic transport properties

In general, PEO-salt complexes, including those containing multivalent cations, present one of three types of behaviour regarding the dependence of conductivity on temperature  

The conductivity behaviour of an electrolyte according to temperature ascribes it to one of the classes described above, and depends significantly on factors such as presence or absence of solvent and/or water traces, and on the thermal history of the compound, namely the recrystallisation kinetics of the complexes and of the pure PEO, which often exist simultaneously. 

A great number of multivalent polymer electrolytes are semicrystalline in nature and belong to type II or III. One example of type II behaviour is shown by the PEO -Znl2 system, with the variation of ionic conductivity with temperature behaving differently below and above the transition temperature T. For T Tt, the data gave a linear variation due to the existence of crystalline compounds below T, and the Arrhenius law was applied. For T Tt, the data produced a convex variation, in accordance with the amorphous regime observed above T, and the VTF law was applied. 

Examples of type I PEO-MX (M = multivalent cation, X = anion) include complexes of PEO-based calcium and barium salts, PEO-based zinc chloride (in composition O/Zn = 4 and 8), PE0-Cu(C104)2 (certain compositions) and PE0-Tm(S03CF3)3. When the polymeric system is predominantly amorphous, conductivity-temperature behaviour is sometimes better described by the VTF law, for instance for the gel polymer electrolyte studied by Pandey et a/., where the addition of liquid electrolyte provokes substantial conformational changes in the crystalline texture of the host polymer due to immobilisation of the liquid electrolyte in the gel system. The polymer crystallinity almost disappears and the VTF equation applies to the a-T relationship. 

Some polymer electrolytes show conductivity temperature dependence that falls outside the three types described above, with neither the Arrhenius law nor the VTF (or WLF) law being followed in the temperature ranges studied. Here, if there are no phase changes, effects associated with ionic aggregate equilibria are likely, superimposed on the simple variation in ionic mobility. In all cases, it is important to consider not only this parameter, but also the number and types of charge carriers, which are influenced by the ionic association that probably exists in ionic transport.  

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Figure 10.3.2 shows the crystal structure of a-Agl and the possible positions of the Ag+ ions, the mobility of which accounts for the prominent ionic transport properties of a-Agl as a solid electrolyte. 

The ionic transport properties of fluorite-type oxide phases (see Chapter 2), another important family of solid electrolytes, are also discussed in subsequent chapters. Briefly, for the well-known zirconia electrolytes, Zr itself is too small to sustain the fluorite structure at moderate temperatures doping with divalent (Ca + ) or trivalent (e.g., Y " ", St " ", Yb " ") cations stabilizes the high-temperature polymorph with the cubic fluorite-type structure. Due to the electroneutrahty condition, anion vacancies are formed ... 

Royce, B.S.H. (1973) The effect of structure and ionic transport properties of calcium apatite. /. Rhys. Suppl., 34, 327-332. 

Such information as the energy of an unspecified excited state, the spatial distribution of radiative energy absorbed, or ionic transport properties can be crucial to developing connections between fundamental properties and detailed mechanisms. Chapters 7 and 9 contain several examples of the role of electronic structure in photodecomposition and initiation processes involving electric fields and radiation. 

Structure of PFSA Cation Exchange Membranes. In the early 1970s a perfluorosulfonlc acid lonomer was developed for use in electrochemical applications, especially the chloralkall process for the production of chlorine and caustic (1 3). The structure of these lonomers Is shown In Figure 2. The acid form of the lonomer can be easily neutralized to cationic form by reaction with appropriate base such as NaOH. The mechanical, chemical, and Ionic transport properties of these membranes have been extensively studied (11)-16). Mathematical models of the transport of electrolytes through lEMs have been developed (17-18). 

Silicate apatites present several limitations for their potential use as SOFC electrolyte. One of the main drawbacks of apatite-type materials resides in the difficulty in preparing dense ceramic materials, which are needed for SOFC operation. On the other hand, degradation of the ionic transport properties with time in reducing atmospheres at high temperatures has been reported for these materials, which was ascribed to silica migration and volatilisation in the ceramic surface (Yaremchenko et al, 2004).The apatite structure allows a large number of cation substitutions. Among them, the partial substitution of Sb+ by AP+ seems to enhance the ionic conductivity and partially suppress silicon volatilisation (Shaula et a/., 2005,2006). 

The absorption of KOH electrolyte by the SPE membrane is very crucial, because the higher KOH electrolyte content is beneficial for higher ionic conductivity. It would be necessary to have higher concentration of hydroxyl ions (OH ) in polymer matrix. After PVA was blended with PAA, the typical (101) crystalline peak of PVA at 26=19° was significantly reduced [50,51]. The XRD spectra for the PVA/PAA membranes were shown in Fig. 6. This is very helpful to enhance the ionic transport property since there is more amorphous domain available for ion transport. It also improves the absorbility of KOH solution in PVA/PAA membrane due to the higher hydrophilicity property of PAA. 

Experimental results indicate that the ionic transport property for the PVA-based SPE is highly dependent on both the alkali salt and the solution concentration. All the values of anionic transport numbers for different PVA-based SPEs with KOH solution are much higher than those with alkaline NaOH and LiOH solutions. This trend is consistent with literature results [58] that ion movement in polymer is related to polymer segmental motion, and the order of ionic conductivity has been K >Na >Lr. 

Equation 3 is a very important link between the respective limiting values 2 and Z)°° that are characteristic ionic transport properties without disturbance by ionic interaction (infinite dilution). Examples in different solvents [3] are given in Table 1. 

Ionic transport properties like ion mobilities and the related conductivities and diffusion coefficients Di are measurable quantities that permit the development of helpful concepts of electrolyte solution theories. At dilute and moderate concentrations, the models in use are very satisfying, whereas at high concentrations they still... 

Goodenough JB (2004) Electronic and ionic transport properties and other physical aspects of perovskites. Rep Prog Phys 67(11) 1915-1993... 

Dai Chi-An, Chang Chun-Jie, Kao An-Cheng, et al. Polymer actuator based on PVA/ PAMPS ionic membrane Optimization of ionic transport properties. Sensor. Actuat. A.- Physical. 155 no. 1 (2009) 152-162. 

Reinforcement by the incorporation of electrically conductive OD/1D/2D/3D carbon nanoparticles into polymer matrix is a promising approaeh to achieve improved electro-chemo-mechanical properties including enhanced ionic transport properties and tunable mechanical stifiSiess over pristine polymers. Therefore, conductive... 

In order to obtain the exact limiting law for any ionic transport property, it is sufficient to consider a two-point probability flux conservation law along with the assumption of Brownian motion for the ions. 

Siedlarek H, Wagner D, Fischer WR, Paradies HH (1994) Microbiologically influenced corrosion of copper the ionic transport properties of biopolymers. Corrosion Sci 36 1751—1763... 

Sitte, W., Bucher, E.,Benisik A Preis W., (2001) Oxygen nonstoichiometry and ionic transport properties of Lao.4Sro.6Co03-5,. Spectrochimica Acta, 2001, Part A57, 2071-2076... 

Bassat, J. M. Odier, P. Villesuzanne, A. Marin, C. Pouchard, M., Anisotropic ionic transport properties in La2Ni04+s single crystals. Solid State Ionics 2004,167 (3-4), 341-347. 

Yang, C.C., Lin, S.J., Wu, G.M. (2005) Study of ionic transport properties of alkaline poly(vinyl) alcohol-based polymer electrolytes. Materials Chemistry and Physics, 92, 251-255. 

Shin J H, Passerini S, Shin J H and Passerini S (2004) PEO-LiN.S02CF2(Cp3)2 Polymer Electrolytes V. Effect of Fillers on Ionic Transport Properties, J. Electrochem. Soc., 151, pp. A238-A245. 

FERRY A, Effects of dynamic spatial disorder on ionic transport properties in polymer electrolytes based on poly(propylene glycol)(4000) , J Chem Phys, 1997,107(21), 9168-9175... 

Morphological and crystallographic structures characteristics and influence on ionic transport properties... 

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