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PEMs randomly sulfonated

Sulfonated poly(arylene ether)s (SPAEKs) have also been developed for application in PEMs, with sulfonated poly(ether ether ketone) (SPEEK) (9a) as the archetypical example of this group. The base polymer of SPEEK is commercially available and relatively cheap, and sulfonation is a straightforward procedure using concentrated sulfuric acid. At sufficient levels of sulfonation, proton conductivity values for SPEEK are comparable to or higher than those of Nafion. However, this does lead to random copolymers where there... [Pg.142]

There have been few synthetic reports employing these monomers beyond the Ballard work, most likely as a result of presumed high cost and monomer availability. However, the performance and stability demonstrated by these materials in fuel cells may spur further developments in this area. The above-reported copolymers are believed to be random systems both in the chemical composition of the copolymer backbone and with regard to sulfonic acid attachment. Novel methods have been developed for the controlled polymerization of styrene-based monomers to form block copolymers. If one could create block systems with trifluorostyrene monomers, new morphologies and PEM properties with adequate stability in fuel cell systems might be possible, but the mechanical behavior would need to be demonstrated. [Pg.352]

As an extension of the previous work, copolymers based on partially sulfonated ethylene—styrene pseudorandom interpolymers have also been employed instead of the block copolymers (Figure Due to the unique nature of the polymerization catalyst, styrene residues are separated by at least one ethylene residue and the acid groups are distributed randomly along the chain. This material provides an economical and unique counterpoint to the sulfonated SEES PEMs, where the sulfonic acid groups are bunched together in the styrene blocks. Controlling the styrene content in each material provides a route to control the level of sulfonation and resultant ion exchange capacity of the PEM. [Pg.353]

These customer-synthesized new polymers are made of chains with either random or block co-polymers on a laboratory scale by Hickner et al. The MW and the ratio of the random and block segments can be well controlled. The sulfonated groups can be introduced directly or modified after polymer synthesis. The preliminary results showed some promise for PEM fuel cell and DMEC applications with low gas/methanol crossover. [Pg.283]

Novel approaches in PEM synthesis focusing on cheaper, usually fluorine-free PEMs and membranes capable of sustained fuel cell operation at elevated temperatures, have been reviewed in Ref. 75. Mature fuel cell membranes have been casted from sulfonated poly(arylene ether sulfone) (BPSH) random (statistical) copolymers [76]. [Pg.460]

Park et al. summarized the properties of sulfonated hydrocarbon PEMs shown in Eigure 21.54. Nafion 112 with lEC of about 0.91 mequiv. g was used as a reference sample. Hydrocarbon-based random copolymers without specific functionality or side chain were compared with Nafion. Hydrocarbon-based random copolymers without specific functionality or side chain show similar or lower water uptake values than Nafion with the similar lECs at 25°C. Additionally, they exhibit much lower proton condnc-tivity as compared to Nafion with the same lEC. The poor performance of hydrocarbon-based random copolymer is caused by the inefficient aggregation of sulfonic acid gronps that are attached to the backbone directly (withont side chain). In contrast, the snlfonic acid groups of Nafion are decorated at the side chains, and even at low lEC valne, the... [Pg.607]

In their next study, Kawakami et al. addressed issues surrounding the design of the PEM for fuel cells, and more specifically, the role of the polymer architecture in proton conductivity and gas permeability [266]. Erom the previous study, Kawakami et al. showed that the polymer architecture (for example, graft polymer structures) helped enhance proton conductivity and suppressed gas permeability [260]. Taking that idea one step further, they synthesized and examined the PEM properties of sulfonated block (S-b-Pl), graft (S-g-PI), random-graft (S-rg-PI), and... [Pg.167]

Block copolymers combing PBI with other types of macromolecular units have also been developed for superior membrane properties, as shown in Fig. 7.6. Two types of copolymers have been prepared, characterized, and evaluated as fuel cell electrolytes. One is the sulfcmated copolymer containing PBI and snUrmated polymer moieties for low temperature PEMs in both PEM fuel cells and direct methanol fuel cells (DMFCs) [123-126]. The other is the random copolymer containing PBI and poly(imine/ amide) moieties [127, 128]. For the sulfonated PBI copolymers, benzimidazole monomers... [Pg.160]

The water content is the state variable of PEMs. Water uptake from a vapor or liquid water reservoir results in a characteristic vapor sorption isotherm. This isotherm can be described theoretically under a premise that the mechanism of water uptake is sufficiently understood. The main assumption is a distinction between surface water and bulk water. The former is chemisorbed at pore walls and it strongly interacts with sulfonate anions. Weakly bound bulk-like water equilibrates with the nanoporous PEM through the interplay of capillary, osmotic, and elastic forces, as discussed in the section Water Sorption and Swelling of PEMs in Chapter 2. Given the amounts and random distribution of water, effective transport properties of the PEM can be calculated. Applicable approaches in theory and simulation are rooted in the theory of random heterogeneous media. They involve, for instance, effective medium theory, percolation theory, or random network simulations. [Pg.366]

The properties of sulfonated PEMs are controlled by (1) the chemical structures of the polymer repeat unit (2) the polymer molecular weight and molecular weight distribution (3) the microstructnre of the polymers (including the cis- and transorientations the random, alternating, and block structures and the linear, branched, and cross-linked structures) (4) the degree of sulfonation of the polymers (5) the morphology of the solid PEMs, that is, the hydrophobic and hydrophilic domain... [Pg.9]

Aromatic polymers, such as PESs, poly(ether ether ketone)s, and polyimides, are used as polymer matrices for PEMs due to the high performance described earlier. Sulfonated PEMs are generally prepared by two methods the postsulfonation of aromatic polymers usually leading to a random functionalization along the polymer main chains and direct copolymerization of the sulfonated monomers to afford random copolymers. Both methods are discussed in the following. [Pg.137]

On the other hand, three sulfonated aromatic polymers with different seqnences, that is, alternating, random, and multiblock sequences (Figure 4.25), were studied in order to better understand the relationship between the molecular structure, morphology, and properties of the PEMs as a function of the RH [38]. [Pg.162]

The conductivity of Naflon is higher than those of the sulfonated aromatic PEMs (4.2 mS/cm at 50% RH). The relative slopes of the log (conductivity) versus RH plots for each polymer are of interest and can illustrate the effect of humidity on each membrane s conductivity. The slope indicates the dependency of proton conductivity on the RH. Both Naflon and the multiblock copolymer exhibit similar slopes ( 0.026), and their slopes are lower than those of other random and alternating polymers, meaning that their conductivity is less dependent on the RH than those of the random and alternating polymers. To obtain more information on the difference in... [Pg.162]

FIGURE 4.25 Structure of sulfonated aromatic PEMs used (a, Ph-PEEKDK alternating polymer b, BPSH-35 random copolymer c, BPSH-15-PI-15 multiblock copolymer). [Pg.165]


See other pages where PEMs randomly sulfonated is mentioned: [Pg.55]    [Pg.69]    [Pg.87]    [Pg.137]    [Pg.158]    [Pg.350]    [Pg.59]    [Pg.78]    [Pg.285]    [Pg.293]    [Pg.160]    [Pg.312]    [Pg.62]    [Pg.64]    [Pg.56]    [Pg.120]    [Pg.155]    [Pg.407]    [Pg.121]    [Pg.48]   
See also in sourсe #XX -- [ Pg.69 ]




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