Proton exchange membrane ionomer

ESR spectroscopy, used in the direct detection or spin trapping modes, is a sensitive method for the detection of polymer fragments and for determining the degradation mechanism. Recent applications for the study of stability in ionomer membranes used as proton exchange membranes in fuel cells demonstrate the capability of ESR to detect details that cannot be obtained by other methods. 

Xie, T., Hayden, C., Olson, K. and Healy, J. 2005. Chemical degradation mechanism of perfluorinated sulfonic acid ionomer. In Advances in materials for proton exchange membrane fuel cell systems, Pacific Grove, CA, Feb. 20-23, abstract 24. 

Song, M. K., Kim, Y. T., Fenton, J. M., Kunz, H. R. and Rhee, H. W. 2003. Chemically modified Nafion (R)/poly(vinylidene fluoride) blend ionomers for proton exchange membrane fuel cells. Journal of Power Sources 117 14-21. 

Proton Exchange Membrane (PEMFC) These cells use a perfluorinated ionomer polymer membrane which passes protons from the anode and cathode. They operate at about 80 °C. These are being developed for use in transport applications and for portable and small fuel cells. 

The PE MFC has a solid ionomer membrane as the electrolyte, and a platinum, carbon-supported Pt or Pt-based alloy as the electrocatalyst. Within the cell, the fuel is oxidized at the anode and the oxidant reduced at the cathode. As the solid proton-exchange membrane (PEM) functions as both the cell electrolyte and separator, and the cell operates at a relatively low temperature, issues such as sealing, assembly, and handling are less complex than with other fuel cells. The P EM FC has also a number of other advantages, such as a high power density, a rapid low-temperature start-up, and zero emission. With highly promising prospects in both civil and military applications, PEMFCs represent an ideal future altemative power source for electric vehicles and submarines [6]. 

The FEMTO ST Institute [Pichonat et al.] demonstrated an alternative solution which does not use an ionomer for the proton exchange membrane but consists in a porous silicon membrane with a proton conducting silane grafted on the pores walls [16,17]. A demonstrated fuel cell with dimensions of 8 x 8 mm and an active area of 7 mm with this membrane achieved a maximum power density of 58 mW cm at room temperature with H., as fuel. 

Hiramitsu Y, Mitsuzawa N, Okada K and Hori M (2010), Effects of ionomer content and oxygen permeation of the catalyst layer on proton exchange membrane fuel cell cold Journal of Power Sources, 195,1038-1045. 

This chapter will introduce the reader to the reasons for miniaturizing fuel cells and to the specifications required by this miniaturization. It will then show what kinds of fuel cells can fit to these specifications and which fuels can be employed to supply them. The techniques presently used for the realization of miniature fuel cells will be described, underlining particularly the growing part of the microfabrication techniques inherited from microelectronics. It will present an overview on the apphcations of these latter techniques on miniature fuel cells by presenting several solutions developed throughout the world. It will finally detail, as an example, the complete fabrication process of a particular microfabricated fuel cell based on a silane-grafted porous silicon membrane as the proton-exchange membrane instead of a cortunon ionomer such as Nafion . 

Ghielmi, A., Vaccarono, P., Troglia, C., and Arcella, V. (2005) Proton exchange membranes based upon the short-side-chain perfluorinated ionomer. J. Power Sources, 145, 108-115. 

The ionic groups, although present in small amoimts, dominate the viscoelastic behavior of ionomers, their transport properties and their ability to sorb a variety of solvents moreover, the ion effect is specific. In terms of morphology, the presence of ions leads to microphase separation into ionic and nonpolar domains. Increasing interest in structural aspects of ionomers is closely related to their numerous applications as bulk materials, in various devices, as catalysts, in controlled release systems, and as proton exchange membranes (PEM) in fuel cells (71). 

Schaberg MS, Abulu JE, Haugen GM, Emery MA, O Conner SJ, Xiong PN, Hamrock SJ (2010) New multi acid side-chain Ionomers for proton exchange membrane fuel cells. ECS Trans 33(l) 609-627... 

Figure 18.4. Transport of Pt from a smaller particle to a larger particle by coupled transport of Pt throu the liquid and/or ionomer and the transport of electrons through the carbon support when the Pt particles are in contact with electronically conducting carbon [32]. (Reproduced by permission of ECS— The Electrochemical Society, from Virkar AV, Zhou Y. Mechanism of catalyst degradation in proton exchange membrane fuel cells.)...

The proton exchange membrane can be a source of fluoride ions as well [143]. Hydroxyl radicals, formed via crossover gases or reactions of hydrogen peroxide with Fenton-active contaminants (e.g., Fe +), could attack the backbone of Nafion, causing the release of fluoride anions these anions in turn promote corrosion of the fuel cell plates and catalyst, and release transition metals into the fuel cell [143]. Transition metal ions, such as Fe, then catalyze the formation of radicals within the Nafion membrane, resulting in a further release of fluoride anions. On the other hand, transition metal ions also can cause decreased membrane and ionomer conductivity in catalyst layers, as discussed in section 2.4 of this chapter. 

The membrane electrode assembly (MEA) in a proton exchange membrane (PEM) fuel cell has been identified as the key component that is probably most affected by the contamination process [1]. An MEA consists of anode and cathode catalyst layers (CLs), gas diffusion layers (GDLs), as well as a proton exchange membrane, among which the CLs present the most important challenges due to their complexity and heterogeneity. The CL is several micrometers thick and either covers the surface of the carbon base layer of the GDL or is coated on the surface of the membrane. The CL consists of (1) an ionic conductor (ionomer) to provide a passage for proton transport ... 

Arico AS, Baglio V, Di Blasi A et al (2006) Proton exchange membranes based on the short-side-chain perfluorinated ionomer for high temperature direct methanol fuel cells. Desalination 199 271-273... 

A modem FC used in transportation and other applications is shown in Fig. 2. Its key elements are the electrodes, the catalyst, and the proton exchange membrane (PEM) the cell is fueled by hydrogen or methanol at the anode and oxygen or air at the cathode. The membrane electrode assembly (MEA) that is the heart of ECs includes the proton exchange membrane, a polymer modified to include ions, typically sulfonic groups an ionomer In the presence of water, ionomers self-assem-ble into microphase separated domains that allow the movement of in one direction only, from the anode to the cathode. The membrane performance was first demonstrated by Nafion, the ionomer made by DuPont, which consists of a perflu-orinated backbone and pendant chains terminated by sulfonic groups, -SOs . Nafion was the major component in the PEMEC developed by General Electric for... 

---