Proton-conducting gel polymer electrolyte

Hashmi, S. S. A. 2014. Quasi-solid-state pseudocapacitors using proton-conducting gel polymer electrolyte and poly(3-methyl thiophenej-ruthenium oxide composite electrodes. Journal of Solid State Electrochemistry 18 465-475. 

Proton-conducting gel polymer electrolyte (GPE) based on poly(vinylidene fluoride)-hexafluoropropylene (PVdF-HPA) or polyimethyl methacrylate-heteropolyacid) (PMMA-HPA)... 

Proton-conducting gel polymer electrolyte (GPE) doped with 12-PWA... 

The solid electrolytes in fuel cells must function as a separation membrane so that oxygen and hydrogen will not mix, and as a proton conductor. The polymer electrolyte membrane that has an acid side group exhibits these two functions. However, in order to exhibit conductivity, it must contain water because the acid group must dissociate. Hence, solid electrolyte in broad sense is the gel that contains water. 

S.S. Sekhon, H.P. Singh, Proton conduction in polymer gel electrolytes containing chlo-roacetic acids. Solid State Ionics, 175 (2004) 545-548. 

Abstract The chapter begins by discussing the characters and composition of polymer electrolytes for electrochromic devices. It then describes the four types of the polymer electrolytes dry solid polymer electrolyte, gel polymer electrolyte, porous gel polymer electrolyte and composite solid polymer electrolyte, their preparation procedures and properties especially ion conductivity of the samples. Finally, new types of polymer electrolytes including proton-conducting, alkaline, single ionic polymer electrolytes and electrolytes with ionic liquids are also introduced. 

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. 

Many approaches have been developed for the production of ionic liquid-polymer composite membranes. For example, Doyle et al. [165] prepared RTILs/PFSA composite membranes by swelling the Nafion with ionic liquids. When 1-butyl, 3-methyl imidazolium trifluoromethane sulfonate was used as the ionic liquid, the ionic conductivity ofthe composite membrane exceeded 0.1 S cm at 180 °C. A comparison between the ionic liquid-swollen membrane and the liquid itself indicated substantial proton mobility in these composites. Fuller et al. [166] prepared ionic liquid-polymer gel electrolytes by blending hydrophilic RTILs into a poly(vinylidene fiuoridej-hexafluoropropylene copolymer [PVdF(HFP)] matrix. The gel electrolytes prepared with an ionic liquid PVdF(HFP) mass ratio of 2 1 exhibited ionic conductivities >10 Scm at room temperature, and >10 Scm at 100 °C. When Noda and Watanabe [167] investigated the in situ polymerization of vinyl monomers in the RTILs, they produced suitable vinyl monomers that provided transparent, mechanically strong and highly conductive polymer electrolyte films. As an example, a 2-hydroxyethyl methacrylate network polymer in which BPBF4 was dissolved exhibited an ionic conductivity of 10 S cm at 30 °C. 

The next entry is for Nafion, a proton-conducting fluorosulfonic acid ionomer material which in membrane form is widely used in PEM fuel-cell technology. The conductivity value quoted is for a fully hydrated membrane at an ambient temperature. Note that the conductivity is less than that of a comparable aqueous acid solution, for example 0.5 M sulfuric acid, but by a factor of only 3-4. Heavily hydrated Nafion membranes contain a lot of water, and consequently they behave a lot like aqueous acid solutions. The next three entries are for various gel and solid-polymer electrolytes containing lithium salts. All these material are membranes some contain some potentially volatile solvents, while others do not. Conductivities for these materials are low relative to true liquid solvents but they are still well within the range of usable values for electrochemical experiments. The semi-solid character of these materials, combined with their near-zero volatility (for solid-polymer electrolytes which do not contain volatile solvents), makes them suitable for use under high-vacuum conditions which makes them potentially useful for fabrication of electrochemical devices which are targeted for use in vacuum or under conditions which could otherwise result in solvent loss by evaporation. 

In summary, the agglomerates within the PAM matrix can form a structure with both gel and crystal zones when they contact with aqueous electrolyte. The gel zone is composed of Pb-O-OH polymer chains, which can serve as the paths for proton transfer, and the crystal zone can serve as the electron transfer paths. In this way, the PAM can have both high electron and proton conductions for the charge and discharge processes. 

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