Alkaline ionomer

AEMs and alkaline ionomers (anionomers) are key to the successful implementation of AMECs. Anion-exchange membranes have, for a long time, been used as separation membranes for seawater desalination, the recovery of metal ions from wastewaters, electrodialysis and bio-separation processes, for example [16-26]. These membranes may, however, not be stable or conductive enough to be applied in AMECs. AEMs used in early AMEC studies were reviewed in 2005 [1] and included polybenzimidazole (PBl) doped with KOH, epichlorohydrin polymer... 

Recent intensive studies have, however, been reported to lead to AEMs with high ionic conductivities, reportedly comparable to Nalion . These promising AEMs [11, 45-51] are still to be evaluated in AMFCs. Most hydrocarbon AEMs are soluble in various solvents, which is potentially useful for the formulation of alkaline ionomers required for the preparation of high-performance membrane electrode assemblies (MEAs). If the conductive properties reported can be translated into high power outputs, then AMEC performances comparable to those of PEMFCs can be expected in the near future. 

Scheme 2.3 The formation of SIONl alkaline ionomer (anionomer) by cross-linkage of poly (vinylbenzyl chloride) with tetramethylhexanediamine (TMHDA)...

The development of alkaline ionomers is one of the major challenges for the development of high-performance alkaline membrane containing fuel cells. In state-of-the-art AMFC technology, the role of the ionomer has not been fully investigated or understood alkaline ionomer solutions/dispersions, comparable to the Nafion dispersions used in PEMFCS, remain highly sought after. 

Copolymers of methacrylic add and ethylene termed as ethylene ionomers have been used as the base polymer for binding alkali, alkaline earth and transition metal ions. Organic amines such as n-hexylamine, hexamethylene tetraamine, 2,2,6,6-tetramethyM-hydroxy piperazine, ethylene diamine and polymeric diamines such as silicone diamine, polyether diamine and polymeric diamines such as silicone diamine, polyether diamine and polyamide oligomers considerably enhance the complex formation characteristics of Zn(II) ethylene ionomers thereby enhancing the physico-chemical properties [13]. 

O. Bagel, B. Limoges, B. Schollhorn and C. Degrand, Subfemtomolar determination of alkaline phosphatase at a disposable screen-printed electrode modified with a perfluorosulfonated ionomer film, Anal. Chem., 69 (1997) 4688-4694. 

Kreuer K-D, Wohlfarth A, de Araujo CC, Fuchs A, Maier J. Single alkaline-ion (Li+, Na+) conductors by ion exchange of proton-conducting ionomers and polyelectrolytes. Chem-PhysChem. 2011 12(14) 2558-60. 

Self-diffusion coefficients of polyvalent cations in these perfluorinated ionomer membranes have not been reported. It can be inferred from the use of the sulfonate membranes as Donnan dialysis devices that transport of cations such as CuflT), Mg(II), and Al(III) under a concentration gradient is rapid. Also, column chromatographic separation of the alkaline-earth ion is readily accomplished with a powdered Nafion perfluorosulfonate polymer, which is again an indication of facile diffusion of these cations within the polymer phase. 

The averages of the Tg values for the alkali metal and alkaline earth forms of each of the degrees+of sulfonation are included in Table 2. Two trends are evident. First, among the M T ionomers Tg depends largely on the degree of sulfonation rather than on the detailed properties of the cation. Second, among the M ionomers there is little dependence on either the cation or the degree of sulfonation up to at least 12.7 mole percent. At y = 16.7, each of the cation PSSA series has a value of Tg of about 126°C. 

The Tg data helps in understanding the varied behavior of the PSSA ionomers. They show that up to about 13 mole percent sulfonation, that is when there are 8 or more styrene units between anionic sites, the Tg s of alkaline earth PSSA s do not vary strongly with either the nature of the cation or with y. The Tg s of alkali metal PSSA s in this composition range do vary with y but they do not vary systematically... 

Firstly, Nafion and other perfluorinated sulfonic acid ionomers will be discussed, along with inorganic- and organic-Nafion based composites. Secondly, we will introduce non-fluorinated single and composite membranes, including membranes for high temperature DAFC. Finally we will discuss anion conducting membranes for alkaline DAFC. 

Wang J, Wang J, Li S, Zhang S. Poly(arylene ether sulfone)s ionomers with pendant quaternary ammonium groups for alkaline anion exchange membranes preparation and stability issues. J Membr Sci 2011 368(l-2) 246-53. 

Fuel cell CLs are the key components in the entire fuel cell device because the reactions such as hydrogen—oxidation reaction (HOR) at anode and the ORR at cathode occur inside the CLs. Particularly, in order to carry out the ORR, the catalyst particles inside the cathode CL must be in contact with each other for electrical conductivity and also in contact with protonic conducting (in acidic PEM fuel cells), or hydroxide conducting (in alkaline PEM fuel cells) ionomer for ionic conductivity. In addition, there must be some channels within the CL for transporting the reactants and the products. In other words, the catalyst particles must be in close contact with each other, with the electrolyte, and also with the adjacent diffusion medium (DM). Moreover, the reactants gas O2) and the produced water travel mainly through the voids, so the CL must be porous enough to allow gas to diffuse to the reaction sites and liquid water to wick out. 

Rotomolding additives include nucleating agents, such as, inoiganic substances such as talcum, metal oxides such as titanium dioxide or magnesium oxide, phosphates, carbonates or sulfates of, preferably, alkaline earth metals organic compounds such as mono- or polycarbojQ lic acids and their salts, e g., 4-tert-butylbenzoic add, adipic acid, diphenylacetic acid, sodium succinate or sodium benzoate polymeric compounds such as ionic copolymers (ionomers). ... 

Bunazawa H, Yamazaki Y (2008) Influence of anion ionomer content and silver cathode catalyst on the performance of alkaline membrane electrode assemblies (MEAs) for direct methanol fuel cells (DMFCs). J Power Sources 182(1) 48-51... 

Piana M, Boccia M, Filpi A, Flammia E, Miller HA, Orsini M, Salusti F, Santiccioli S, Ciardelli F, Pucci A (2010) H2/air alkaline membrane fuel cell performance and durability, using novel ionomer and non-platinum group metal cathode catalyst. J Power Sources 195(18) 5875-5881... 

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