Perfluorosulfonic acid membranes PFSA

In the development of fuel-cell technology based on this unique polymer electrolyte, special chapters in electrochemical science and engineering have emerged, addressing the fuel-cell ionomeric membrane itself and the optimized fabrication of MEAs. The invention of Nafion, a poly(perfluorosulfonic acid) (poly(PFSA)) at DuPont in the 1960s, was, in fact, a key (if not the key) milestone in the development of PEFC technology. The chemical and mechanical properties of such poly(PFSA) extruded membranes, which are based on a perfluorocar-bon backbone, enabled to achieve stable materials properties and, consequently,... 

Kreuer et al. [25] investigated the membrane properties, including water sorption, transport (proton conductivity, electro-osmotic water drag and water diffusion), microstructure and viscoelasticity of the short-side-chain (SSC) perfluorosulfonic acid ionomers (PFSA, Dow 840 and Dow 1150) with different lEC-values. The data were compared to those for Nafion 117, and the implications for using such ionomers as separator materials in direct methanol and hydrogen fuel cells discussed. Tire major advantages of PFSA membranes were seen to be (i) a high proton conductivity. 

The diaphragm may be replaced by a cation exchange membrane which is suitable for high concentrated hydrochloric acid like Nafion (DuPont, perfluorosulfonic acid polymer, PFSA, see entry Chlorine and Caustic Technology, Membrane Cell Process ). This membrane has almost no usual porosity and is nearly exclusively permeable for ions including a hydration shell of some water molecules. Thus, product quality is significantly increased, process operation can be simplified, and cell voltage is reduced by about 0.3 V [1, 6]. However, the mechanical durability... 

The principle of operation is shown in Fig. 2. Chlorine gas is produced at the anode (especially optimized dimensionally stable anode) with an anolyte feed concentration of 14 wt % HCl. Anode and cathode are separated by a cation exchange membrane (perfluorosulfonic acid polymer, PFSA, e.g., Nafion of DuPont). The ODC is based on a conductive carbon cloth which operates simultaneously as a gas diffusion layer because a suitable material is incorporated. The oxygen reduction reaction (5) takes place in three-phase boundaries of a thin, porous catalyst layer on the surface. 

Aquivion E87-12S short-side chain perfluorosulfonic acid (SSC-PFSA) membrane with equivalent weight (EW) of 870 g eq and 120 pm thickness produced by Solvay Specialty Polymers was tested in a polymer electrolyte membrane water electrolyser (PEMWE) and compared to a benchmark Nation N115 membrane (EW 1100 g eq ) of similar thickness [27]. Both membranes were tested in conjunction with in-house prepared unsupported Ir02 anode and carbon-supported Pt cathode electrocatalyst. The electrocatalysts consisted of nanosized Ir02 and Pt particles (particle size 2-4 nm). The electrochemical tests showed better water splitting performance for the Aquivion membrane and ionomer-based membrane-electrode assembly (MEA) as compared to Nafion (Fig. 2.21). Lower ohmic drop constraints and smaller polarization resistance were observed for the electrocatalyst-Aquivion ionomer interface indicating a better catalyst-electrolyte interface. A current density of 3.2 A cm for water... 

Cations, showing stronger affinity with the sulfonic group of the PFSA (perfluorosulfonic acid) membrane than H+, occupy active sites. Flence, membrane bulk properties, namely ionic conductivity, water content, and FI+ transference number, are changed. 

Perfluorinated membranes are still regarded as the best in the class for PEM fuel cell applications. - These materials are commercially available in various forms from companies such as DuPont, Asahi Glass, Asahi Chemical, 3M, Gore, and Sol-vay. Perfluorosulfonic acid (PFSA) polymers all consist of a perfluorocarbon backbone that has side chains terminated with sulfonated groups. 

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]. 

We consider transport within the family of perfluorosulfonic acid (PFSA) membranes, such as Nafion. The membrane is taken as the porous medium, and only two species are assumed present in the pore fluid, proton carriers (species i = 1) and water (i = 2). Furthermore we assume that the dominant proton carrier is hydronium. 

Abstract This article outlines some history of and recent progress in perfluorinated membranes for polymer electrolyte fuel cells (PEFCs). The structure, properties, synthesis, degradation problems, technology for high temperature membranes, reinforcement technology, and characterization methods of perfluorosulfonic acid (PFSA) membranes are reviewed. 

Keywords Analysis Cross leak degradation High temperature membrane Perfluorosulfonic acid PFSA Reinforcement... 

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]. 

Fig.1 Chemical structure of perfluorosulfonic acid (PFSA) membranes...

In PEMFC, the current state-of-the-art fuel cell technology primarily involves the use of perfluorosulfonic acid (PFSA) membrane as electrolyte. PFSA membranes are composed of carbon fluorine backbone chains with perfluoro side chains containing... 

Ma, Xu, Liu, and Sun (2010) used perfluorosulfonic acid-poly(vinyl alcohol)-Si02/ poly(vinyl alcohol)/polyacrylonitrile (PFSA-PVA-Si02/PVA/PAN) bifunctional hollow-fiber composite membranes. The catalytic and the selective layer of the membrane were independently optimized. These membranes were synthesized by dipcoating. The performance of these bifunctional membranes was evaluated by dehydrating the ternary azeotropic composed of a water, ethanol, and ethyl acetate system (top product of a reactive distillation process of esterification of acetic acid with ethanol), obtaining separation factors of water/ethanol up to 379. An extensive assessment on the esterification reaction of ethanol-acetic acid was later published (Lu, Xu, Ma, Cao, 2013). In this case, the reaction equilibrium was broken in less than 5 h, and a 90% conversion of acetic acid was achieved after 55 h. 

Product Information, 2005, DuPont Nafion PFSA Membranes N-112, NE-1135, N-115, N-117, NE-1110 Perfluorosulfonic Acid Polymer. NAEIOI. 

Table 4.2 shows the -SO3H (i.e., H+) concentrations for Nafion-like iono-mers (d = 2.0 g cm ) with different EWs. Smaller EWs result in higher proton concentrations. For known perfluorosulfonic acids (PFSAs), the EW typically ranges between 800 and 1100. When the EW is lowered further, the mechanical properties of the membrane are not adequate for long-time operations. The results shown in Table 4.2 are plotted in Figure 4.7. 

Copolymers of tetrafluoroethylene and sulfonic acid functional per-fluorinated monomers (e.g., Nafion, Dow s perfluorosulfonic acid (PFSA)) have high water permeability. Water transport through these ionomer membranes has been investigated. The non-Fickian diffusion process is analyzed by a thermodynamic approach. The results provide some useful insights into the behavior of these materials as dehydration membranes. 

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. 

The MEA is composed of three main parts, e.g., polymer electrolyte membrane (PEM), gas diffusion medium, and catalyst layer (CL). The membrane, with hydrophilic proton-conducting channels embedded in a hydrophobic structural matrix, plays a key role in the operation of PEFCs. The PEMs for PEFCs commonly use perfluorosulfonic acid (PFSA) electrolytes such as Nation , with the chemical structure shown in Fig. 2, because of its high proton conductivity as well as chemical and thermal stability [1]. The gas diffusion medium (GDM), including both the microporous layer (MPL) and the gas diffusion layer (GDL), which typically is based on carbon fibers, is also an important component. The GDM is designed with three distinct... 

Hydrogen oxidation reaction (HOR) Membrane electrode assembly (MEA) Oxygen reduction reaction (ORR) Perfluorosulfonic acid (PFSA)... 

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