Stability PFSA chemical

Improvement in PFSA Chemical Stability through End-Group Modification... 

Recently, DuPont has introduced a new membrane that is an improvement in comparison to earlier versions NR-111, NR-112, and NR-211. DuPont Nation XL membrane is an extended-lifetime reinforced membrane based on chemically stabilized PFSA/PTFE copolymer in the acid (H-f) form. The reinforcement improves the handling of the membrane and its physical properties. When the reinforcement is combined with the chemically stabilized polymer, the membrane... 

The E79-03S SSC, chemically stabilized PFSA membrane developed by Solvay has a thickness of 30 pm (dry form) and an equivalent weight of 790 g eq [26]. The relevant properties of this ionomer have been discussed above. It is stressed that this ionomer is characterized by both larger crystallinity and higher glass transition temperature than LSC polymers at a given equivalent weight [24]. 

Styrenic polymers, which are easy to synthesize and modify, were studied extensively in the early literature. One example is BAM made by Ballard Advanced Materials (see chemical structure below). This membrane is 75 pm thick and has an ion exchange capacity of about 1.1 to 2.6 meg/g. Its chemical stability is not as good as PFSA even with its perfluorinated backbone. Ballard claimed that this membrane could last for several hundred hours under low RH operating conditions. It is no longer in production due to its high cost and the lack of availability of the monomer. 

The electrolyte membrane presents critical materials issues such as high protonic conductivity over a wide relative humidity (RH) range, low electrical conductivity, low gas permeability, particularly for H2 and O2, and good mechanical properties under wet-dry and temperature cycles has stable chemical properties under fuel cell oxidation conditions and quick start-up capability even at subfreezing temperatures and is low cost. Polyperfluorosulfonic acid (PFSA) and derivatives are the current first-choice materials. A key challenge is to produce this material in very thin form to reduce ohmic losses and material cost. PFSA ionomer has low dimensional stability and swells in the presence of water. These properties lead to poor mechanical properties and crack growth. 

In spite of the documented, relatively high chemical stability of poly(PFSA) membranes in the fuel-cell environment, recent extensive work looking into the origins of performance loss observed in PEFCs has revealed important mechanisms of degradation that apply to perfluorinated membranes (while being further amplified in nonperfluorinated membranes). An important mechanism of membrane... 

The membrane material most often used in fuel cells today is Nation , made by DuPont. Nation is the product name of a perfluorosulfraiic acid/polyethylene copolymer (PFSA/PTFF) that clearly meets the specifications for thermal and chemical stability and high levels of protmi conductivity and electrical resistance. Other perfluorinated membranes are now commercially available in addition to Nation DOW Membrane from Dow Chemical Corp. and a membrane made by... 

PFSA membranes possess high proton conductivity in the range of 0.1 S cm" at 80°C and good chemical as well as mechanical stability. The superior stability of Nafion is a consequence of the PTFE-based structure that is chemically... 

In order to solve this chemical stability problem, a new proprietary PFSA ionomer synthesis procedure has been developed at DuPont that results in a reduction of the reactive end groups. This approach has been referred as chemical stabilization (CS) technology. Fluoride emission from chemically stabilized polymer in a Fenton s test was found to be eight times lower than a nonchemically stabilized polymer. 

In the new XL membrane, DuPDnt has reportedly incorporated advanced chemical stabilization technology that further reduces the number of reactive end groups in the polymer chain and thus further reduces the reR during operation. Due to these advancements in the chemical stabilization technology, XL membrane shows 14 times lower FER than standard reinforced PFSA membrane (see Figure 21.29). 

Perfluorosulfonic acid (PFSA) membranes as shown in Fig. 1 were first developed for fuel cells by DuPont as Naflon and installed into the Biosatellite spacecraft in 1967 [1,2]. Various types of PFSA polymers, such as Flemion , Aciplex , and Dow membrane, were developed subsequently. They have excellent chemical stability, high proton conductivity, and high water diffusivity in a wide range of temperatures, brought about by the nature of fluorinated compounds and these non-cross-linked structures [3-5]. 

For DAFC operated at room and moderate temperamres (lower than 80 °C) perfluoiinated sidfonic acid ionomers (PFSA), mainly Nafion (DuPunt), have been the most studied and used in direct methanol (DMFC) and ethanol fuel cells (DEFQ due to its excellent proton cmiductivity and chemical stability [16, 17]. 

Perfluorosulfonic add (PFSA) membranes continue to be the industry standard for low-temperature PEMFCs due to their excellent proton conductivity, mechanical and chemical stability that is difficult to surpass. The Nafion membrane produced by DuPont has been the most studied (Mauritz and Moore, 2004 Grot, 2008). Nafion membranes are coded according to the polymer equivalent weight (EW) (first two digits), the membrane thickness (in mil, 1/1000 inch, corresponding to 25 pm) - third, or third and fourth digits) thus Nafion N117 is polymer EW 1100,7 mil thickness. In parallel with these developments, advances have been made on related perfluorinated ionomers that differ from the Nafion -type polymer... 

Due to fluorination, PFSA materials are relatively more costly than non-fluorinated hydrocarbon membranes. The latter such as poly (ether ether ketone) and poly (arylene ether sulfone) have also been widely investigated for fuel cell applications. In addition to lower cost, some of them also have better dimensional stability with regard to hydration levels. The problem is their lower chemical stability in the fuel cell environment. 

As mentioned above, perfluorosulfonic acid (PFSA) membranes like Nation (Dupont) are CEMs of very high chemical and thermal stability. In a highly sophisticated composition, such membranes are used as separators in industrial chlor-alkali electrolysis. Most research in the area of SPE electrosynthesis has also been done using Nation membranes. 

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