Solid polymer electrolytes polyelectrolytes

A membrane ionomer, in particular a polyelectrolyte with an inert backbone such as Nation . They require a plasticizer (typically water) to achieve good conductivity levels and are associated primarily, in their protonconducting form, with solid polymer-electrolyte fuel cells. 

Note 2 The terms polyelectrolyte, polymer electrolyte, and polymeric electrolyte should not be confused with the term solid polymer electrolyte. 

In polyelectrolyte gels the variation of pH or salt concentration (cs) causes a swelling or shrinkage. Therefore, in this case chemical energy is transformed to mechanical work (artificial muscles). An increase of cs (or a decrease of temperature) makes the gel shrink. Usually, the shrinking process occurs smoothly, but under certain conditions a tiny addition of salt leads to the collapse of the gel [iii, iv]. Hydration of macroions also plays an important role, e.g., in the case of proton-conductive polymers, such as -> Nafion, which are applied in -rfuel cells, -> chlor-alkali electrolysis, effluent treatment, etc. [v]. Polyelectrolytes have to be distinguished from the solid polymer electrolytes [vi] (- polymer electrolytes) inasmuch as the latter usually contain an undissociable polymer and dissolved small electrolytes. 

The definition of a solid polymer electrolyte should not be confused with that of a polymeric electrolyte [whose macromolecules contains ionic or ionizable groups, or both). Polyelectrolytes can be either synthetic or natural [12,16-18, 20-23]. 

The most simple and efficient approach is based on gelation which is a simple method that allow a good compromise between the retention of the IL and its fluidity inside the polymeric network. These so called ion gels are simpler than solid polymer electrolytes and exhibit improved conductivities. In fact ion gels hold both the processability and mechanical properties of polymers, but with added physico-chemical properties and were primary developed as replacements for current solid-state polyelectrolytes in energy devices, such as dye-sensitized solar cells, supercapacitors, lithium ion batteries, and fuel cells. (Fernicola et al., 2006 Galinski et al., 2006 Le Bideau et al., 2011 Lu et al., 2002 Mazille et al., 2005 Stephan, 2006)... 

When Nafion was discovered in 1962, it was considered to be a solid polymer electrolyte due to the presence of a sulfonic acid group attached to the perfluorinated chain (Fig. 11.3). It is not a true solid proton conductor as ion transport occurs via a quasi-liquid phase as in other polyelectrolytes. In... 

FORSYTH M, SUN J, ZHOU F and MCFARLANE D R (2003), Enhancement of ion dissociation in polyelectrolyte gels , Electrochim Acta, 48 2129-2136 GAVELiN p, uuNGBACK R, JANNASCH p and WESSLEN B (2002), AmphiphiUc solid polymer electrolytes . Solid State Ionics, 147(3—4) 325-332 GRAY EM (1991), Solid polymer electrolytes-fundamentals and technological applications, New York WUey Publishers. 

The electrical properties of polyelectrolyte complexes are more closely related to those of biologically produced solids. The extremely high relative dielectric constants at low frequencies and the dispersion properties of salt-containing polyelectrolyte complexes have not been reported for other synthetic polymers. Neutral polyelectrolyte complexes immersed in dilute salt solution undergo marked changes in alternating current capacitance and resistance upon small variations in the electrolyte concentration. In addition, their frequency-dependence is governed by the nature of the microions. As shown in... 

Fundamental investigation of the system at the molecular level. This requires investigations of the structure of the solid/liquid interface, namely the structure of the electrical double layer (for charge-stabiUsed suspensions), adsorption of surfactants, polymers and polyelectrolytes and conformation of the adsorbed layers (e.g., the adsorbed layer thickness). It is important to know how each of these parameters changes with the conditions, such as temperature, solvency of the medium for the adsorbed layers, and the effect of addition of electrolytes. 

FIGURE 2.81 Schematic diagrams of (a) dry solid-state polymer electrolyte (e.g., PEO/Li+), (b) gel polymer electrolyte, and (c) polyelectrolyte. (Zhong, C. et al. 2015. A review of electrolyte materials and compositions for electrochemical supercapacitors. Chemical Society Reviews 44 7484-7539. Reproduced by permission of The Royal Society of Chemistry.)... 

Preparation of solid-state electrochemical devices require that conventional fluid solution electrolytes be replaced with a solid ion conductor. Solid electrolytes have been widely studied, primarily for the development of high energy-density batteries. Classes of solid state electrolytes include classical solids such as the p-aluminas, polyelectrolytes such as Nation, gel electrolytes and polymer electrolytes. For the purpose of developing solid-state electrochemical devices, polymer electrolytes are promising, because they are easily confined to microelectrochemical arrays/and are gas permeable. 

Snyder JF, Ratner MA, Shriver DF (2002) Polymer electrolytes and polyelectrolytes Monte Carlo simulations of thermal effects on conduction. Solid State Ionics 147 249... 

Teachers need to be aware of two different uses of the term electrolyte . In the strict sense, an electrolyte is a liquid that cm undergo electrolysis. This can be a single substance, as in the case of a molten salt, or a solution. The most typical electrolytes are the aqueous solutions of salts (in general of ionic compounds), of acids, and of bases. By extension, we also call electrolytes the pure substances (solid, liquid, or gaseous) that, when dissolved in water, provide liquid electrolytes. Some biological substances (such as DNA or polypeptides) and synthetic polymers (such as polystyrene sulfonate) contain multiple charged functional groups and their dissolution leads to electrolyte solutions these are termed polyelectrolytes. 

Similar particulate systems with a polyelectrolyte polymer core have been developed for the immobilisation of nanoparticles and enzymes (Lu et al, 2009b). In both cases the core of the particles was used for stabilising the catalytic systems, preventing their agglomeration and for easier handling and recovery after the completion of the reaction. In the case of the enzymes, polyelectrolyte polymer core particles present a better way of enzyme immobilisation than immobilisation on solid surfaces. The mild conditions inside the poly electrolyte core preserve the native conformation and biological activity of enzymes. 

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