Acid anionic polymer electrolyte

Water was born to conduct protons (see Special Issue Is life possible without water [67]). The conductance of distilled water is miserable due to a negligible concentration of free protons (10 mol/liter), but the proton mobility in water is approximately five times higher than the mobility of an alkali cation (e.g. Na" ), an object of similar size as the hydronium (HaO ) ion [68]. So, donated protons can run fast through the aqueous phase. Excess protons result from dissociation of acidic molecules or molecular groups, e.g. in solutions of strong acids, hydrated polymer-electrolytes, or proteins. In acidic solutions both the protons and counter-anions are mobile. In polymer-electrolyte membranes and in proteins only protons are mobile in the connected aqueous phase while the counter anions are mostly a part of an immobile skeleton. 

As is well known, and as discussed by Neyerlin and others, there is an increase in polarization losses with phosphoric acid-based fuel cells, in comparison to low-temperature PFSA-based fuel cells, and this effect is thought to be due to the presence of phosphoric acid and/or its anions that adsorb onto the surface of the catalyst [47]. Because of this, high-temperature stacks based upon phosphoric acid-doped polymer electrolyte membranes are larger in order to get the same power output. The overall question is whether the benefit in system simplification overcomes the need for larger stacks, so that there is an overall net system benefit. Reducing the effect of the adsorbed anion species would, of course, have significant benefit at the stack and system levels. 

Excess protons in aqueous electrolyte result from the dissociation of acid molecules or molecular groups in solutions of strong acids, hydrated polymer electrolytes, or proteins. In acidic solutions, both protons and counter-anions are mobile. In PEMs, only protons are mobile while anions are immobilized at the macromolec-ular matrix or skeleton of the pore network. 

Recent developments in AAEMs have opened up the possibiUty of an alkaline analog of the acidic solid polymer electrolyte fuel cell. This could utilize the benefits of the alkaline cathode kinetics and at the same time eradicate the disadvantages of using an aqueous electrolyte. As the AAEM is also a polymer electrolyte membrane (sometimes abbreviated as PEM), some clarity in abbreviations is required. In this chapter, PEM refers only to the proton exchange membrane fuel cells (acidic), AAEM refers to the anion exchange membrane H2/O2 fuel cells, and AFC exclusively refers to the aqueous electrolyte alkaline H2/O2 fuel cells. Anion exchange membranes are also employed in alkaline direct alcohol fuel cells, discussion of which will refer to them as ADMFC/ADEFC (methanol/ ethanol). 

CE has been used for the analysis of anionic surfactants [946,947] and can be considered as complementary to HPLC for the analysis of cationic surfactants with advantages of minimal solvent consumption, higher efficiency, easy cleaning and inexpensive replacement of columns and the ability of fast method development by changing the electrolyte composition. Also the separation of polystyrene sulfonates with polymeric additives by CE has been reported [948]. Moreover, CE has also been used for the analysis of polymeric water treatment additives, such as acrylic acid copolymer flocculants, phosphonates, low-MW acids and inorganic anions. The technique provides for analyst time-savings and has lower detection limits and improved quantification for determination of anionic polymers, compared to HPLC. 

The lithium transference number (l,) of these organoboron polymer electrolytes was evaluated by combination of dc polarization and ac impedance methods, as reported by Evans et al44 (Table 1). The observed t+ at 30°C was 0.50-0.35, indicating that anions were significantly trapped in these systems. Owing to the stronger Lewis acidity of the alkylborane unit, alkylborane-type polymers showed relatively higher t+. 

As a result, the acid strength of the proton is approximately equivalent to that of sulfuric acid in nonaqueous media. In view of the excellent miscibility of this anion with organic nonpolar materials, Armand et al. proposed using its lithium salt (later nicknamed lithium imide , or Lilm) in solid polymer electrolytes, based mainly on oligomeric or macro-molecular ethers. In no time, researchers adopted its use in liquid electrolytes as well, and initial results with the carbonaceous anode materials seemed promising. The commercialization of this new salt by 3M Corporation in the early 1990s sparked considerable hope that it might replace the poorly... 

Lithium Salts Based on Heterocyclic Anions. Lithium salts based on organic anions where the formal charge is delocalized throughout substituted heterocyclic moieties were also reported sporadically, which included, for example, lithium 4,5-dicyano-l,2,3-triazolate ° and lithium bis(trifluoro-borane)imidazolide (Lild). ° The former was developed as a salt to be used for polymer electrolytes such as PEO, and no detailed data with respect to electrochemistry were provided, while the latter, which could be viewed as a Lewis acid—base adduct between LiBp4 and a weak organic base, was intended for lithium ion applications (Table 13). 

Nafion is a copolymer of poly(tetrafluoroethylene) and polysulfonyl fluoride vinyl ether. It has fixed anions, which are sulfonic acid sites, and consequently, by electroneutrality, the concentration of positive ions is fixed. Furthermore, the transference number of protons in this system is 1, which greatly simplifies the governing transport equations, as seen below. There can be different forms of Nafion in terms of the positive counterion (e.g., proton, sodium, etc.). Most models deal only with the proton or acid form of Nafion, which is the most common form used in polymer-electrolyte fuel cells due to its high proton conductivity. 

Gelatin is hydrolyzed by most of the proteolytic systems to yield amino components. Further, it reacts with acids and bases, aldehydes and aldehydic sugars, anionic and cationic polymers, electrolytes, metal ions, plasticizers, preservatives, and surfactants. Even, exposure to stress conditions of humidity, temperature, and/or light leads to perceptible changes. 

Catalysts for anion-exchange membrane fuel cells are for the use in the alkaline medium. Thus, much more materials could be applicable as catalysts than those for polymer electrolyte fuel cells, which should be stable in acidic electrolyte. 

When the content of CajfPO ) in the NCPE is increased to 20% the ionic conductivity of the NCPE decreases. This decrease in the ionic conductivity can also be attributed to the change in the crystallinity of PEO in the nanocomposite polymer electrolytes (Capuglia et al., 1999). According to Scrosati and co-workers (Scrosati et al., 2001), the Lewis acid groups of the added inert filler may compete with the Lewis acid lithium cations for the formation of complexes with the PEO chains as well as the anions of the added lithium salt. In the present study, the filler nano CajfPO lj, which has a basic center can react with the Lewis acid centers of the polymer chain and these interactions lead to the reduction in the crystallinity of the polymer host. Nevertheless, the result provides LL conducting pathways at the filler surface and enhances ioiuc transport. 

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