Sulfonated membranes

After the initial work on asymmetric sulfonated polyphenylene oxide membranes, sulfonated polysulfone was subsequently examined by several research groups. However, the appearance of patents in 1973 and 1977 by Rhone-PoulencM 8S covering asymmetric membranes of sulfonated polysulfones appeared to dampen such research efforts. Also, a basic problem with sulfonated polysulfone was the fact that salt rejections fell rapidly when a critical level of sulfonation was exceeded, but water fluxes were too low until this sulfonation level was exceeded. 

Figure 4.8 Current efficiency versus fixed ion concentration of a cation exchange membrane in the electrolysis of a sodium chloride solution. Cation exchange membrane sulfonated styrene—divinylbenzene type. Anolyte saturated NaCl catholyte 3.0 N NaOH current density 10Adm 2 at 70 °C.

Figure 5.2 Comparison of transport number of calcium ions relative to sodium ions in a phosphonic acid membrane with that in a sulfonic acid membrane. ( ) sulfonic acid membrane (A) phosphonic acid membrane. 1 1 mixed salt solutions of calcium chloride and sodium chloride of different concentrations were electrodialyzed.

Jaafar J, Ismail AF, Mustafa A (2007) Physicochemical study of poly (ether ether ketone) membranes sulfonated with mixtures of finning sulfiuic acid and sulfuric acid for direct methanol fuel cell application. Mater Sci Eng A 460-461 475-484... 

Yang and Manthiram studied SPEEK membranes for use in a DMEC (Yang and Manthiram 2003). It was reported that a membrane with 50% degree of sulfonation (DS) exhibited comparable DMEC performance to Naflon 115 at 65°C, while the methanol crossover was two times lower than the Naflon membrane. Sulfonated poly(ether ketone) (SPEK), sulfonated poly(ether ketone ketone) (SPEKK), and sulfonated poly(ether ether ketone ketone) (SPEEKK) come from the same family as SPEEK and therefore their characteristics are quite similar. 

These membranes are based on perfluorinated polymers that will withstand oxidatWe conditions and high temperatures that would be destructive to hydrociubon-based membranes. Sulfonic or caiboxylic acid groups, or both, are affixed chemically to the perfluorinated polymers to impart cation-exchange characteristics. 

D. Zhao, J. Li, M.K. Song, B. Yi, H. Zhang, M. Liu, A durable alternative for proton-exchange membranes sulfonated poly(benzoxazole thioether sulfone)s, Adv. Energy Mater. 1 (2) (2011)203-211. 

Key words electrolyte, membrane, proton conductor, perfluorosulfonic acid, ionomer, acid-doped membranes, sulfonic acid, phosphonic acid, heterocycle,... 

Boaventura et al. [12] reported the generation of polytriazole based proton conducting membranes. Sulfonated polytriazole membranes were doped with three different agents IH-benzimidazole-2-sulfonic acid, benzimidazole and phosphoric acid. Figure 1.13 also shows the storage modulus and tan 6 curves for pure polymer... 

Several materials have been studied on the goal of producing cost-effective PFMs [55-62]. Some of these are PBI-based membranes, polysterene membranes, sulfonated polyimide, cross-Unked poly(vinyl alcohol), and phosphobenzene, sulfonated poly(aryl ether ketone) —based manbranes. Sulfonation of aromatic thermoplastics such as polyether sulfone, polybenzimidazole, polyimides, and poly(ether ether ketone) makes them proton conductive suitable for fuel cell... 

Compared with perfluorinated sulfonic acid membranes, sulfonated poly(aryl ether ketone) is reported to have a smaller characteristic sq>aration length and wida distribution with more dead-end channels and a largo- internal interface between the... 

Perhaps the simplest modification of Nafion for DMFCs was carried out by Tricofi [28], who doped Nafion 117 with Cs cations. The decrease in size of hydrated micellar domains, upon snbstituting a portion of the membranes sulfonate sites with cesium, caused the methanol permeability to fall. The ratio of proton conductivity to methanol permeability, which reflects membrane selectivity, increased by a factor of 2.5 when Nafion 117 in the H+ form was fnlly exchanged with cesium. To prevent cesium fiom leaching ont of the membrane during fuel cell operation, Tricofi proposed adding a suitable amount of Cs salt to the methanol/water feed mixture. 

Shahi, V.K. (2007) Highly charged proton-exchange membrane sulfonated poly(ether sulfone)-silica polyelectrolyte composite membranes for fuel cells. Solid State Ionics, 177, 3395-3404. 

Suda et al. [288] reported the synthesis and characterization of a series of sulfonated star-hb polyimides (S-hb-Pls) without any crosslinking for use as proton exchange membranes. Sulfonated anhydride-terminated polyimides with different molecular weights (M v = 59,000, 200,000 and 300,000 Da) based on monomer combination 1,4,5,8-naphthalene tetracarboxylic dianhydride/4,4 -diaminobiphenyl 2,2 -disulfonic acid (NTDA/BDSA) were synthesized using different molar ratios of BDSA NTDA. The amine-terminated hb-Pl based on monomer combination 4,4-(hexafluoroisopropylidene)diphthalic anhydride/tris(4-aminophenyl)amine (6EDA/TAPA) was also prepared. Scheme 33 shows the monomer combinations used for the preparation of (S-hb-Pl). 

Klebe reported that the chlorosulfonation reaction on P3O was best carried out in nitromethane solvent. Sulfonation under these conditions takes place exclusively on the backbone of the polymer. When carried out in chloroform solution cross-linking reactions took place. This polymer was utilized by Hodgdbn to make a fuel cell membrane. Sulfonated PPO and P3O undergo slow desulfonation reactions at 100°C in the presence of water. In order to force the sulfonation reaction to take place on the pendent phenyl groups, and hence give a more hydrolytically stable polymer, the polymer was first brominated on the backbone followed by sulfonation. ... 

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