Perfluorosulfonic acid based

Perfluorosulfonic acid-based membranes are some of the most conunonly studied membranes in hydrogen pumping. Lee et al. [16] studied... 

Fig. 5 Ion-cluster model of a perfluorosulfonic acid-based IPMC. (a) Ion-cluster network mode and (b) schematic view of the stress valance in the ion cluster (Reproduced from Zhu et al. 2013a)...

Water Flux in Polymer Electrolyte Membranes Water flux in the solid electrolyte membrane of the PEFC must be understood to grasp the concept of a local water balance in the fuel cell. From Chapter 5, we know that the ionic conductivity of perfluorosulfonic acid-based solid polymer electrolytes is a strong function of water content. Within the electrolyte, there are four basic modes of transport, as schematically illustrated in Figure 6.21 ... 

An adequate structure of polymer molecules promotes the advantageous phase separation into hydrophobic and hydrophilic domains upon water uptake. The most notable class of membranes based on this principle are the perfluorosulfonic acid ionomers (PFSI), Nafion [26] and similar membranes [27]. In these membranes, perfluorosulfonate side chains, terminated with hydrophilic —SO3H groups, are attached to a hydrophobic fluorocarbon backbone. The tendency of ionic groups to aggregate into ion clusters due to the amphiphilic nature of the ionomer leads to the formation of basic aqueous units. At sufficient humidity these units first get connected by narrow channels and then may even fuse to provide continuous aqueous pathways [28]. 

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,... 

In April 1975, Asahi Chemical started operation of a membrane chlor-alkali plant with a capacity of 40,000 MT/Y of caustic soda using Nafion perfluorosulfonic acid membrane. In 1976, this membrane was replaced by perfluorocarboxylic acid membrane developed by Asahi Chemical. The total caustic production capacity of plants based on Asahi Chemical s membrane chlor-alkali technology using perfluorocarboxylic acid membrane will reach 520,000 MT/Y in 1982, at seven locations in various countries. 

Cation, anion, and water transport in ion-exchange membranes have been described by several phenomenological solution-diffusion models and electrokinetic pore-flow theories. Phenomenological models based on irreversible thermodynamics have been applied to cation-exchange membranes, including DuPont s Nafion perfluorosulfonic acid membranes [147, 148]. These models view the membrane as a black box and membrane properties such as ionic fluxes, water transport, and electric potential are related to one another without specifying the membrane structure and molecular-level mechanism for ion and solvent permeation. For a four-component system (one mobile cation, one mobile anion, water, and membrane fixed-charge sites), there are three independent flux equations (for cations, anions, and solvent species) of the form... 

A amperometric device based on carbon monoxide inhibition of hydrogen oxidation kinetics using either a perfluorosulfonic acid pol5mier electrolyte or an inorganic acid electrol5de is being evaluated for the low temperature application. 

It has been well established that the presence of perfluorosulfonic acid ionomeric materials, such as Nafion -H, at the electrocatalyst site of Pt-based... 

Numerous polymers have been studied for their potential apphcation in PEMFCs. Based on their chemical structure, these polymers can be categorized into (a) vinylic polymers, (b) aromatic polymers, and (c) polymer blends and composite/hybrid polymers. Generally, vinylic polymers are synthesized by addition polymerization, while aromatic polymers are synthesized by step-growth polymerization. The most studied vinylic polymers for PEMFC applications are perfluorosulfonic acid ionomers (PFSls), in particular Nation , and styrene sulfonic acid-based polymers. Chemical structures of representative vinyhc PEMs are shown in Scheme 2. 

While a munber of alternative polymer membranes have been developed. Nation is still considered the benchmark of proton conducting polymer membranes, and has the largest body of research hterature devoted to its study. Alternative polymer membranes are almost invariably compared to Nation . Nation is a free radical initiated copolymer consisting of crystaUiz-able, hydrophobic tetrafluoroethylene and a perfluorinated vinyl ether terminated by perfluorosulfonic acid. Nation 117 possesses an equivalent weight of 1100 (EW = mass of dry ionized polymer (g) in the protonic acid form that would neutralize one equivalent of base). Thus, there are 13 perfluoro-methylene groups (-CF2-) ( = 6.5) between pendent ionic side chains. 

Y. Chang, G.F. Brunello, J. Puller, M.L. Disabb-Miller, M.E. Hawley, Y.S. Kim, M.A. Hickner, S.S. Jang, C. Bae, Polymer electrolyte membranes based on poly(arylene ether sulfone) with pendant perfluorosulfonic acid, Polym. Chem. 4 (2) (2013) 272-281. 

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. 

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... 

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