PFSIs

Scattering from PFSI Solutions and Recast 4543 Films... 

More recently, Loppinet and co-workers have used both SAXS and SANS (with contrast variation methods) to characterize the morphology of dilute PFSI solutions having a volume fraction of polymer less... 

PAN in [HMIM PFsI/aqueous systems as a function of aqueous phase pH. From reference [8]. 

Phaseolus vulgaris (kidney bean) PFSI Chymotrypsin, Trypsin [253]... 

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]. 

The developed approach will be applied to model membranes whose psds closely resemble those of Nafion and similar PFSI membranes [60]. A common parameterization of experimental data for ultrafiltration membranes is given by the so-called logarithmic normal distribution [59],... 

The essential ingredients of the catalyst layer are an electronically conducting matrix of carbon grains, Pt catalyst particles supported on carbon and a protonconducting network of well-humidified PFSI. In addition, Teflon (PTFE) may be added as a binder and hydrophobizing agent. 

A number of different methods exist for the production of catalyst layers [97-102]. They use variations in composition (contents of carbon, Pt, PFSI, PTFE), particle sizes and pds of highly porous carbon, material properties (e.g., the equivalent weight of the PFSI) as well as production techniques (sintering, hot pressing, application of the catalyst layer to the membrane or to the gas-diffusion layer, GDL) in order to improve the performance. The major goal of electrode development is the reduction of Pt and PFSI contents, which account for substantial contributions to the overall costs of a PEFC system. Remarkable progress in this direction has been achieved during the last decade [99, 100], At least on a laboratory scale, the reduction of the Pt content from 4.0 to 0.1 mg cm-2 has been successfully demonstrated. 

According to the porosity data of Uchida et al. [102] the matrix of carbon grains (20-40 nm) forms an agglomerated structure with a bimodal psd. Primary pores (micropores, 5-40 nm) exist within agglomerates, between the carbon grains. Larger, secondary pores (macropores, 40-200 nm) form the pore spaces between agglomerates. The relation between the relative pore volume fractions of the two pore types depends on the contents of PFSI and PTFE. Due to their molecular size these components are not able to penetrate micropores. They affect only the macropore volume. The experimental study revealed that an increased PFSI content leads to a decrease of the macropore volume fraction. The opposite effect was found for PTFE. 

Here, tit is the number of electrons that are transferred in the rate-determining reaction step. At a Pt PFSI interface nt = 1 has been identified [99,110]. The standard exchange current density (in A cm-2)... 

The basic equations of catalyst layer operation, Eqs. (42-46), are valid under the assumption of isothermal, stationary conditions. Furthermore, variations of the water vapor partial pressure are neglected. The water content in the PFSI fractions and the corresponding proton conductivity are, therefore, independent of x- Upon proceeding along x, starting at x = 0 with /p(X = 0) = jo, proton current is gradually converted into C>2 flux jo2 = (j-p(x) — y o)/4. At x = 1 the transformation is complete, yp = 0, since no protons are admitted to pass the interface to the GDF. 

In Sect. 8.2.3.5 we have discussed how for the given parameters that characterize ionic transport, gas transport, and reactivity of the catalyst layer, and a specified target current density, one can choose the layer thickness, which provides minimal voltage losses. The parameters, however, depend on composition, which can be varied to optimize the performance. By composition one may imply the chemical composition of the components. Such variation is a subject of material chemistry. Here we will discuss only the variation of the relative amounts of the distinct components (carbon, Pt, PFSI, PTFE) which is a subject of physics of composites. 

In spite of the widely recognized importance of an advanced catalyst layer design, detailed structural data for catalyst layers are still scarce in the open literature on fuel cells [116, 117]. In one of the rare experimental studies, Uchida et al. showed the effect of the variation of the PFSI (and PTFE) content on catalyst layer performance [101]. An attempt to rationalize the experimentally observed composition dependence theoretically was first undertaken in Ref. 17. The prerequisites for an adequate theoretical study... 

Fig. 17 Comparison of the model calculations with experimental data by Uchida et al.[101, 102], Current-voltage plots for the fuel cell (including voltage losses due to membrane and cathode catalyst layer). The fits are obtained with the percolation properties of Fig. 15, and s = asb = 1.2 A cm-2, / = 10-7 Acm 2, b = 30 mV. A linear relation between PFSI content jupfsi and Xe was used,...

S.L. Kohls, R.D. Noble and C.A. Koval, Effect of molecular structure and equivalent weight on facilitated transport of alkanes in Ag(I)-PFSI membranes, J. Membr. Sci., 1997, 125, 61-73. 

Perfluorosulfonate ionomer (PFSI) - Dow Cemical Company Fig. 1.5. Chemical structures of perfluorosulfonate ionomer materials. 

For the purposes of delineating the scope of the membrane systems considered in this chapter, the generic PFSI chemical structure is defined in Figure 13.1, following the notation used by Tant et al. [1]. All the structures have a common feature they consist of a (presumed) random copolymer of tetrafluoroethylene and perfluorovinyl ether monomer units but differ in terms of the length and distribution of the ionic side groups along the main... 

Figure 13.1 Generic chemical formula of perfluorosulphonate ionomer (PFSI), with variable indices m and n. For Flemion m = 0-1, n = 1-5 Nafion m =, n = 2 Dow m=, n= Aciplex m = 0-2, n = 1-4. Typical molecular weights are estimated to be in the range 10 -10 g moF (Mauritz and Moore [2]), which would correspond a random copolymer with x = 595-5945, y = 91-909 for 1100 EW molecules of Nafion.

Application of Atomistic Modelling to PFSI Membrane Morphology... 

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