Perfluoro sulfonated polymer

Figure 7. Minimum energy conformation of a two-side-chain fragment of a perfluoro sulfonic acid polymer (Dow) with six water molecules, showing the dissociation of both acidic protons.

This concept was applied to fuel cell technology at a very early stage however, performance and reliability of the cells were low due to the dissatisfying membrane properties at that time. The development of perfluoro sulfonate and carboxylate-type membranes, in particular for the chlor-alkaU process, directly fostered the further development of proton-conducting membranes and, as a consequence, also the progress in this type of fuel cell technology (polymer electrolyte fuel cell, PEFC). 

Liu J, Suraweera N, Keffer D J, Cui S and Paddison S J (2010), On the relationship between polymer electrolyte structure and hydrated morphology of perfluoro-sulfonic acid membranes ,/P/zy5 Chem C, 114,11279-11292. 

N.D. (2010) Changes in the chemical stmcture and properties of a perfluoro-sulfonated acid membrane induced by fuel-cell operation. J. Appl. Polym. Sci.,... 

Many different types of polymer membranes containing fixed ionic groups have been explored since. Up to today, the materials of choice are perfluoro sulfonic acid membranes of the Nafion-type (Fig. 2), for the first time described by (jrot [9]. These materials, similar products have later been developed by other companies (Asahi Glass, Asahi Kasei, Solvay, 3M, Gore, etc.), have been continuously improved for their application in fuel cells. A comprehensive overview of membrane development can be found in [10]. 

Polymer Electrolyte Fuel Cells, Membrane-Electrode Assemblies, Fig. 2 Chemical structure of perfluoro-sulfonic acid polymer... 

One of the significant differences between hydrocarbon ionomers and perfluoro-sulfonic acid polymers is add groups. The pKa value of benzenesulfonic acid (PhSOsH) is 2.5 and that of trifluoromethanesulfonic acid (CF3SO3H) is —13. The pKa value was estimated to be ca. 1 for sulfonated polyether ketone and ca. —6 for Nafion membranes [78]. Therefore, the effective proton concentration and proton mobility should be lower in the hydrocarbon ionomer membranes. Without appropriate molecular design such as multiblock copolymer and sulfonic acid clusters as mentioned above, hydrocarbon ionomer membranes lack well-developed ionic channels due to less pronounced hydrophilic and hydrophobic phase separation, which causes the lower proton conductivity at low humidity. 

Harrison DJ, Turner RF, Baltes H (1988) Oiaracterization of perfluoro-sulfonic acid polymer coated enzyme electrodes and a miniaturized integrated potentiostat for glucose analysis in whole blood. Anal Chem 60(19) 2002-2007... 

A very similar idea is the use of ion exchanging polymers into which redox active ions can be incorporated by equilibration with an adherent solution. Sulfonated perfluoro polymers (Nafion), polyvinylsulfonic acid , and polystyrene... 

A second surface modification has been reported by Yamamoto et al. These workers added stearic acid to their carbon paste mixture. This produced an electrode which was relatively insensitive to ascorbic acid and DOPAC relative to dopamine. It is theorized that this electrode works because of electrostatic repulsion of the anionic ascorbate and DOPAC by surface stearate groups. Ionic repulsion has also been employed by covering the surface of the working electrode with an anionic polymer membrane. Gerhardt et al. used Nafion, a hydrophobic sulfonated perfluoro-polymer, to make a dopamine selective electrode. This electrode exhibited selectivity coefficients as large as 250 1 for dopamine and norepinephrine over ascorbic acid, uric acid, and DOPAC. 

M.A.E. Robertson and K.A. Mauritz. Infrared investigation of the silicon oxide phase in [perfluoro-carboxylate/sulfonate (bilayer)]/ [sihcon oxide] nanocomposite membranes. Journal of Polymer Science Part B-Polymer Physics 36, 595-606 1998. 

The most diffused material for membranes is based on co-polymers of tetrafluoroethylene (TEE) with perfluorosulfonate monomers. The resulting co-polymer is constituted by polytetrafluoroethylene polymeric chain (PTFE, commercially known as Teflon) in which some fluorine atoms are substituted by sulfonated side chains. The monomer perfluoro-sulfonyfluoride ethyl-propyl-vinyl ether is used in membranes commercialized by Dupont with the registered trademark Nafion (Fig. 3.2), which is the most well-known material used as electrolyte in PEM fuel cells. 

Perfluorocarbon-sulfonic acid ionomer Perfluoro-sulfonylfluoride ethyl-propyl-vinyl ether Photovoltaic Solid oxide fuel cell Solid polymer electrolyte Thermal energy Tetrafluorethylene... 

Takasaki et al. [47] assigned the chemical shifts of PSEPVE-containing copolymers based on smaller model compounds. The relatively high insolubility of PSEPVE-containing polymers inhibited their ability to produce concentrated samples for 2D-NMR studies. This resulted in spectra with few peaks. Perfluoro(2,5,8-trimethyl-3,6,9-trioxadodecanoyl)fluoride and perfluoro(2-ethoxyethane) sulfonic acid were chosen to represent two halves of PSEPVE. These compounds were then studied with 19f 13c HSQC, F-1 E COSY, and CIGAR-HMBC. 

Other applications of AFM to the characterisation of polymers include polythiophene [9], nitrile rubbers [10], perfluoro copolymers of cyclic polyisocyanurates of hexamethylene diisocyanate and isophorone diisocyanate [11], perfluorosulfonate [12], vinyl polymers [13], polyhydroxybutyrate [14], polyacrylic acid nanogels [15], acrylic copolymers [16, 17], polyurethanes [18, 19], ethylene methacrylate copolymer [4, 20], polyamides [21], polyvinyl pyrrolidone [22], and polyethyl methacrylate dispersions [23], acryloyl chloride [13], aniline-4-sulfonic acid [24], ethylene propylene 5-ethylidene-2-norbornene terpolymer [25] and butylene adipate - butylene terephthalae [26]. 

Nafion is an ionomer that has a hydrophobic tetrafluoroethylene (TFE) backbone and perfluoro alkyl ether (PFAE) side chains terminated with hydrophilic sulfonate salt [1 ], as shown in Fig. 1. It was introduced by DuPont in 1960 and has been used in a variety of applications such as an ion-selective membrane for the Qilor-Alkali process [5, 6], a water transport membrane for humidifiers, and as a strong acid catalyst [7]. Nafion was introduced as a polymer electrol34e membrane (PEM) in fuel cells in the early 1990s [4, 8]. Compared to hydrocarbon membranes, Nafion was chemically more robust in the fuel cell and the acid form has high proton conductivity. There have been many efforts to find alternative membrane materials... 

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