Potential polymer electrolyte

Schonberger, F., Kerres, J. (2007) Novel multiblock-co-ionomers as potential polymer electrolyte membrane materials. Journal of Polymer Science Part A Polymer Chemistry,... 

The most promising fuel cell for transportation purposes was initially developed in the 1960s and is called the proton-exchange membrane fuel cell (PEMFC). Compared with the PAFC, it has much greater power density state-of-the-art PEMFC stacks can produce in excess of 1 kWA. It is also potentially less expensive and, because it uses a thin solid polymer electrolyte sheet, it has relatively few sealing and corrosion issues and no problems associated tvith electrolyte dilution by the product water. 

The experimental setup is shown in Figure 9.23. The Pt-black catalyst film also served as the working electrode in a Nafion 117 solid polymer electrolyte cell. The Pt-covered side of the Nafion 117 membrane was exposed to the flowing H2-02 mixture and the other side was in contact with a 0.1 M KOH aqueous solution with an immersed Pt counterelectrode. The Pt catalyst-working electrode potential, Urhe (=Uwr)> was measured with respect to a reversible reference H2 electrode (RHE) via a Luggin capillary in contact with the Pt-free side of the Nafion membrane. 

As is well documented, formation of chemisorbed oxygen species on a Pt surface at V > 0.75 V occurs in an inert atmosphere on Pt in contact with an aqueous, or hydrous polymer electrolyte, by anodic discharge of water molecules to form OHads on metal sites, according to the Reaction (1.3). It is this chemisorbed oxygen species, derived from water discharge, that will be considered in the following discussion. Significantly, the Reaction (1.3) is associated with a redox potential K(H20)/Pt-OHads which is quite different from the redox potential for the faradaic ORR process,... 

Yasuda K, Taniguchi A, Akita T, loroi T, Siroma Z. 2006b. Platinum dissolution and deposition in the polymer electrolyte membrane of a PEM fuel cell as studied by potential cycling. Phys Chem Chem Phys 8 746-752. 

Behm RJ, Jusys Z. 2006. The potential of model studies for the understanding of catalyst poisoning and temperature effects in polymer electrolyte fuel cell reaction. J Power Sources 154 327-342. 

What can be learnt from XPS about electrochemical processes will be demonstrated and discussed in the main part of this chapter by means of specific examples. Thereby a survey of new XPS and UPS results on relevant electrode materials will be given. Those electrode materials, which have some potential for a technical application, are understood as practical and will be discussed with respect to the relevant electrochemical process. The choice of electrode materials discussed is of course limited. Emphasis will be put on those materials which are relevant for technical solid polymer electrolyte cells being developed in the author s laboratory. 

Design of organoboron polymer electrolytes will continue to have a great deal of potential based on the ability to tailor boron atoms. This is an attractive approach for single ion conductive materials. 

S. Gottesfeld, "Polymer Electrolyte Fuel Cells Potential Transportation and Stationary Applications," No. 10, An EPREGRI Fuel Cell Workshop on Technology Research and Development, Stonehart Associates, Madison, Connecticut, 1993. 

For a fully dissociated but non-ideal polymer electrolyte (i.e. long range ion interactions are present but not ion association) the following expressions for the steady state potential AV, and current may be derived, again assuming reversible electrode behaviour ... 

The DMFC, based on a polymer electrolyte fuel cell (PEFC), uses methanol directly for electric power generation and promises technical advantages for power trains. The fuel can be delivered to the fuel cell in a gaseous or liquid form. The actual power densities of a DMFC are clearly lower than those of a conventional hydrogen-fed polymer electrolyte fuel cell. In addition, methanol permeates through the electrolyte and oxidizes at the cathode. This results in a mixed potential at the cathode (Hohlein et al., 2000). 

In comparison with the surface layer chemistry on active cathode materials where both salt anions and solvents are involved, a general perception extracted from various studies is that the salt species has the determining influence on the stabilization of the A1 substrate while the role of solvents does not seem to be pronounced, although individual reports have mentioned that EC/DMC seems to be more corrosive than PC/DEC. Considering the fact that pitting corrosion occurs on A1 in the polymer electrolytes Lilm/PEO or LiTf/PEO, where the reactivity of these macromolecular solvents is negligible at the potentials where the pitting appears, the salt appears to play the dominant role in A1 corrosion. 

Redox shuttles based on aromatic species were also tested. Halpert et al. reported the use of tetracyano-ethylene and tetramethylphenylenediamine as shuttle additives to prevent overcharge in TiS2-based lithium cells and stated that the concept of these built-in overcharge prevention mechanisms was feasible. Richardson and Ross investigated a series of substituted aromatic or heterocyclic compounds as redox shuttle additives (Table 11) for polymer electrolytes that operated on a Li2Mn40g cathode at elevated temperatures (85 The redox potentials of these... 

The importance of developing pinhole-free, electrolyte films of nanometer thickness is potentially useful for all 3-D battery designs. For this reason, most of this section reviews the synthesis and characterization of this ultrathin polymer electrolyte with an emphasis on topics such as leakage currents and dielectric strength, which become critically important at the nanoscale. A few comments concerning the packaging of 3-D batteries are made at the end. 

Polyphosphazene-based PEMs are potentially attractive materials for both hydrogen/air and direct methanol fuel cells because of their reported chemical and thermal stability and due to the ease of chemically attaching various side chains for ion exchange sites and polymer cross-linking onto the — P=N— polymer backbone. Polyphosphazenes were explored originally for use as elastomers and later as solvent-free solid polymer electrolytes in lithium batteries, and subsequently for proton exchange membranes. 

---