Perfluorocarbon sulfonic acid

The effect of the polymer backbone on the intrinsic chemical reactivity of metal complexes has been studied in aqueous solution and in Nafion (perfluorocarbon sulfonic acid) film 44). Using a model catalyst-substrate system, the independent kinetic effects of reaction site homogeneity, substrate diffusion into the polymer film, and changes on activation parameters have been addressed. The ligand substitution reaction (6), was chosen for this purpose (Py = pyridine and its derivatives). 

Although perfluorocarbon sulfonic acid groups are very stable chemically as well as thermally, perfluorocarbon sulfonyl halide, especially sulfonyl chloride groups, are quite reactive. For example, sulfonyl chloride groups react with oxidants, reductants, various amines, phenol compounds, iodine compounds, etc. and give carboxylic acid, sulfinic acid, sulfonic acid amide, -CF2I and so forth. Some examples of how this feature can be used to generate various kinds of membranes will next be described... 

Other materials being investigated include ferrocene with a bipyridinium salt,234 niobium oxide,235 nickel oxo-hydroxide,236 and cobalt oxohydroxide.237 The last is pale yellow in the reduced state and dark gray in the oxidized state. A typical electrolyte is lithium perchlorate in propylene carbonate. Solid electrolytes, such as a lithium salt (perchlorate, tetrafluoroborate, or triflate), in a polyepoxide238 or in a polyvinyl chloride gel in ethylene carbonate-propylene carbonate,239 lithium iodide in polyvinyl bu-tyral,240 and Naflon H (a polymeric perfluorocarbon-sulfonic acid),241 have also been tested. Some other systems use suspended particles between two panes of glass.242 When the particles are aligned by an electric field, the window becomes transparent. Combination photo-voltaic-electrochromic devices are under study.243... 

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

Figure 6.41 shows an example of the effect of the carrier transport on C02 flux through a cation exchange membrane ion-exchanged with ethylenediamine.237 Because the flux of gas is low due to the tightness of the ion exchange membrane (perfluorocarbon sulfonic acid membrane), the membrane can be swollen... 

Fe(CN)6]3-.332 Another case to obtain quinone and hydroquinone by electrochemical oxidation of benzene with a high current efficiency, an anode modified by a bipolar ion exchange membrane, composed of a protonated poly-4-vinylpyridine layer and a perfluorocarbon sulfonic acid layer, is used. [Fe(CN)6]3 is incorporated in the inner layer (protonated poly-4-vinylpyridine) and is not contained in the solution. Release of [Fe(CN)6]3 from the inner layer is prevented by the outer layer. As a result, redox catalysts, i.e., Cr6+/Cr3+, or [Fe(CN)6]4-/ [Fe(CN)6]3 incorporated in the bipolar ion exchange membrane on the electrode surface accomplish catalysis more efficiently than if they were dissolved in the electrolyte solution.333... 

Perfluorocarbon-sulfonic acid ionomer Perfluoro-sulfonylfluoride ethyl-propyl-vinyl ether Photovoltaic Solid oxide fuel cell Solid polymer electrolyte Thermal energy Tetrafluorethylene... 

The perfluorocarbon sulfonic acid membrane is generally used. At present, Nafion from Du Pont, Dow membrane from Dow Chemical, Asiplex membrane from Asahi Chemicals, and Flemion from Asahi Glass are commercially available. Figure 4 shows their basic structures their exchange capacity is approximately l.OOmeq/g. 

Fig. 4 The structure of various perfluorocarbon sulfonic acid membranes.

Fig. 5 The dependence of the proton conductivity of perfluorocarbon sulfonic acid membranes on water content.

While the perfluorocarbon sulfonic acid membrane has provided satisfactory properties, further improvement is also desired for the membranes that ... 

Very early hydrocarbon-based membranes tested as electrolytes in PEMECs for Gemini space missions, such as sulfonated phenol-formaldehyde resins, sulfonated poly(styrene-divinylbenzene) copolymers, and grafted polystyrene sulfonic acid membranes, were chemically weak, and therefore PEMFCs using these membranes showed poor performance and had only lifetimes of several hundred hours (LaConti et al. 2003). Nafion , a PESA membrane, was developed in the mid-1960s by DuPont (LaConti et al. 2003). It is based on an aliphatic perfluorocarbon sulfonic acid, and exhibited excellent physical properties and oxidative stability in both wet and dry states. A PEMEC stack using Nafion 120 (250- tm thickness, equivalent weight = 1,200) achieved continuous operation for 60,000 h at 43-82°C (LaConti et al. 2003, 2006). A Nafion -based PEMFC was used for the NASA 30-day Biosatellite space mission (LaConti et al. 2003). 

Nafion is probably the most smdied and operated electrolyte for PEM fuel cells, but other perfluorocarbon sulfonic acid membranes firom Dow, Gore, and Asahi Chemicals are also used and investigated [46,76]. Membranes usually have a small... 

---