Fuel cell membrane applications Nafion structure

Furthermore, in 2001, Ballard entered an alliance with Victrex to produce two new membrane alternatives. One membrane is based on sulfonated poly(arylether) ketone (a variant of s-PEEK) supplied by Victrex, which may be better suited to PEM fuel cell fabrication applications. In March 2002, U.S. Patent 6359019 was issued to Ballard Power for a graft-polymeric membrane in which one or more trifluoro-vinylaromatic monomers are radiation graft polymerized to a preformed polymeric base. The structures of BAM membranes have been studied by way of small-angle neutron scattering or SANS. ° The study of the ionomer peak position suggests the existence of relatively small ionic domains compared to Nafion, despite large water content. Phase separation in the polymer matrix is possibly crucial for the manbrane s mechanical and transport properties. 

Recently, polyimides have drawn considerable attention for the development of membranes for fuel cells. In polymer membrane fuel cells, nafion is widely used as membrane. However, the nafion membrane cannot withstand high temperature (>80 °C), so research on the development of polyimide based fuel cell membranes has started [169-173]. Polyimides also find applications in the development of gas separation membranes because of their compact ring structure and less free volume, which restricts the passage of gases. 

The current state-of-the-art proton exchange membrane is Nafion, a DuPont product that was developed in the late 1960s primarily as a permselective separator in chlor-alkali electrolyzers. Nation s poly(perfluorosulfonic acid) structure imparts exceptional oxidative and chemical stability, which is also important in fuel cell applications. 

Nafion materials, and more generally perfluorinated ionomers, are particularly suitable for water and brine electrolysis and, to date, no viable alternative has been found for SPE applications. The dissolution of Nafion membranes allows the preparation of material with high porosity and high electroactive area. Such structures are required for the development of high power density SPE fuel cells. In recent work, Aldebert et al. have presented different methods for the preparation of SPE... 

A rational analysis of filler effects on structural, proton transport properties and electrochemical characteristics of composite perfluorosulfonic membranes for Direct Methanol Fuel Cells (DMFCs) was reported [7]. It has been observed that a proper tailoring of the surface acid-base properties of the inorganic filler for application in composite Nafion membranes allows appropriate DMFC operation at high temperatures and with reduced pressures [7]. An increase in both strength and amount of acidic surface functional groups in the fillers would enhance the water retention inside the composite membranes through an electrostatic interaction, in the presence of humidification constraints, in the same way as for the adsorption of hydroxyl ions in solution [7]. 

In perfluorinated ionomers, a PTFE-based polymeric backbone offers chemical stability from the radical species or acid-base, which causes hydrolytic degradation of the polymer chain. Ionic conductivity is provided by pendant acidic moiety in carboxylate or sulfonate form. There are some reports on perfluorinated carboxylic acid (PFCA) materials, most of which are derived from Nafion [26-29]. However, PFCA is not suitable for fuel cell application due to its low proton conductivity. Perfluorosulfonic acid (PFSA) is the most favored choice among not only perfluorinated membranes but all other ionomers in fuel cell applications. Sulfonic acid form of Nafion is a representative PFSA and thus has been intensively studied since 1960s. Reported chemical structure of Nafion membrane is given in Fig. 13.8. 

Fig. 15.1 Chemical structure of Nafion [42]. (This figure was published in Journal of Membrane Science, Vol. 259, B. Smitha, S. Sridhar, A. A. Khan, Solid Polymer Electrolyte Membranes for Fuel Cell Applications—a review, page 15, Copyright Elsevier, 2005)...

Truffier-Boutry, D., De Geyer, A., Guetaz, L., Diat, O., and Gebel, G. (2007) Structural study of zirconium phosphate-Nafion hybrid membranes for high-temperature proton exchange membrane fuel cell applications. Macromolecules, 40, 8259-8264. 

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