Solid electrolyte sulfonic acid membranes

Figure 3.23 Chemical structure of perfluorocarbon sulfonic acid membranes as solid polymer electrolytes for fuel cells.

Strongly acidic (sulfonic acid) membranes have been identified for use as solid polymer electrolytes in fuel cells [28]. Preparation of these membranes by radiation induced graft copolymerization has been reported and reviewed in various occasions [23,24,27]. Historically, the first radiation grafted sulfonic acid membranes were prepared by Chen et al. [29] through grafting of styrene onto polyethylene (PE) films and used for battery separators and dialysis. However, most of the early woik on radiation-grafted membranes was carried out and reviewed by Chapiro [30]. 

Patri, M., Hande, V. R., Phadnis, S. and Deb, P. C. 2004. Radiation-grafted solid polymer electrolyte membrane thermal and mechanical properties of sulfonated fluormated ethylene propylene copolymer (FEP)-graft-acrylic acid membranes. Polymers for Advanced Technologies 15 622-627. 

Paddison SJ (2003) Proton conduction mechanism at low degrees of hydration in sulfonic acid-based polymer electrolyte membranes. Ann Rev Mater Res 33 289-319 Rasten E, Hagen G, Tunold R (2003) Electrocatalysts in water electrolysis with solid polymer electrolyte. Electrochimica acta 48 3945-3952... 

In earlier investigations by the authors (2,3) solid sulfonic acid resins containing polyarylether and cyano substituents, (II) and (III), respectively, were prepared and used as proton-conductive membranes, electrode electrolytes, electrode paste, and in membrane electrode assemblies. 

Using proton exchange membranes as electrolytes that are quasi-solid may cause a problem with respect to the perfect wetting of the catalyst particles. In spite of this (initial) difficulty of developing solid polymer membrane fuel cells, water-swollen perfluorinated sulfonic acid polymers such as the commercial Nation have been used for fuel cells very early since they offer the following advantages ... 

The most important use of /3-sultones is for the preparation of fluorinated polymers such as Nafion 64. These solid acid catalysts containing perfluorinated sulfonic acid groups have been known for many years and the presence of the electron-withdrawing F atoms increases the acid strength of the terminal sulfonic acid groups, which become comparable to that of pure sulfuric acid. Prior to the last decade, Nafion had been in use as a superacid, a fuel cell electrolyte and as a membrane-ion separator <1996CHEC-II(1B)1083>. 

The PEFC was first developed for the Gemini space vehicle by General Electric, USA. In this fuel cell type, the electrolyte is an ion-exchange membrane, specifically, a fluorinated sulfonic acid polymer or other similar solid polymer. In general, the polymer consists of a polytetrafluoroethylene (Teflon) backbone with a perfluorinated side chain that is terminated with a sulfonic acid group, which is an outstanding proton conductor. Hydration of the membrane yields dissociation and solvation of the proton of the acid group, since the solvated protons are mobile within the polymer. Subsequently, the only liquid necessary for the operation of this fuel cell type is water [7,8],... 

Subsequent to these early developments of alloy electrocatalysts in the PAFC technology, have been attempts to use the same in pefluorinated sulfonic acid fuel cells (solid state membranes such as Nation from Dupont, Dow, Asahi and others). Yeagei has reviewed the effect of different electrolytes on the ORR electrocatalysis. The summaiy of this work was that the solid state peifluorinated acid environment offered a significant advantage over phosphoric acid. These were... 

Solid polymer electrolytes, typically perfluorosulfonic acid (PFSA) membranes, are at the core of Polymer electrolyte membrane fuel cells (PEMFCs). These membranes electrically and mechanically isolate the anode and cathode while, when appropriately humidified, allowing for effective ion migration. Nafion, manufactured by DuPont, is one of the most thoroughly used and studied membranes in the PFSA family. Another family of membranes that holds some promise for use in PEMFCs is the group of sulfonated polyaromatic membranes, typically sulfonated polyetherketones. While research is being performed on other types of membranes, as well as hybrid membranes that might have been better-suited properties, information on these is searce [1-10]. 

Polymer Electrolyte Membrane (PEM) Solid organic polymer poly-perflouro-sulfonic acid 60-100 Electric utility, transportation, portable power Solid electrolyte reduces corrosion, low temperature, quick start-up... 

Nafion membrane is a nonreinforced film based on Nafion ionomers in acid (H" ") form. Under PEM fuel cell operating conditions, the Nafion membrane is the most practical solid electrolyte due to its unique structure, excellent thermal and mechanical stability, and high proton conductivity (but it is also an isolator for electronic conduction). According to the cluster network model [63-66] of Nafion membrane, Nafion contains some sulfonic ion clusters with a diameter of approximately 4nm. The clusters are equally distributed within a continuous fluorocarbon lattice, and are interconnected by narrow channels with a diameter of about 1 nm this provides passages for the transport of protons. Figure 1.8 shows this cluster network model. Proton... 

There is considerable methanol permeation through Nafion, which affects the fuel cell performance in a DMFC. Using doped PBI the same proton conductivity as Nafion can be maintained while virtually eliminating the crossover of methanol. PBI is doped with a conducting solid, usually phosphoric acid, to make it suitable for DMFC applications [55, 56]. In another attempt PBI is modified by sulfonation to make it an intrinsic proton conductor and is deposited onto a layer of Nafion membrane. This gives a composite polymer electrolyte that is a reasonable proton conductor and reduces the crossover of methanol [57]. 

Polymer electrolyte fuel cells (PEFCs) are unique in that they are the only variety of low-temperature fuel cell to utilize a solid electrolyte. The most common polymer electrolyte used in PEFCs is Nafion , produced by DuPont, a perfluorosulfonic ionomer that is commercially available in films of thicknesses varying from 25 to 175 pm. This material has a fluorocarbon polytetrafluoroethylene (PTFE)-kbone with side chains ending in pendant sulfonic acid moieties. The presence of sulfonic acid promotes water uptake, enabling the membrane to be a good protonic conductor, and thereby facilitating proton transport through the cell. This chapter reviews PEFC development, structure, and properties and presents an overview of PEM technology to date. 

One of the first attempts to use a polymeric ion exchange membrane as a solid electrolyte for fuel cells was described by Thomas Grubb of GE in 1959. Initially, between 1959 and 1961, polysulfuric sulfonic acid (PSSA) membranes were used. The early versions of the PEFC, as used in the NASA Gemini spacecraft, had a lifetime of only about 500 h because of membrane degradation, but that was sufficient for those limited early missions. The development program continued... 

Lufrano, F Baglio, V., Di Blasi, O., Staiti, P Antonucci, V., and Aric6, A.S. (2012) Solid polymer electrolyte based on sulfonated polysulfone membranes and acidic silica for direct methanol fuel cells. Solid State Ionics, 216, 90-94. 

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