Eva Wallnöfer

Sulfonated Poly-Aryl-Ether-Ketones for Applications in Carbon-Nano-Fiber based Membrane-Electrode-Assemblies

Aromatic polymers, in particular poly-arylen-sulfide or poly-arylen-ether-etherketones (PEEK), are in the focus of research groups worldwide to replace Nafion membranes in Polymer-Electrolyte Fuel Cells (PEMFC). The above mentioned polymers are treated with a sulfonation reagent in a halogenated hydrocarbon to attach the functional acid groups on the polymer backbone. With the use of an electrophile aromatic substitution reaction, cation exchange materials on the base of PEEK are synthesized and Membrane-ElectrodeAssemblies (MEA) for PEMFC applications are produced. These polymers have the intrinsic property of a high stability against chemical and thermal influences which are present in PEMFCs. Via the substitution of -Protons with acid-groups, e.g. sulfonic acid, the hydrophilic properties and the proton conductivity in electrochemical, aqueous systems can be increased. This proton conductivity is depending on the dispersion of the substituted functional groups [1]. The variation of the sulfonation degree of MEAs based on sulfonated PEEK showed that even a doubling of the ionic groups from 20 % to 40 % led a moderate increase of power density [2]. The sulfonated PEEK-membranes are characterised exsitu by water-uptake measurements and ion-exchange capacity. The MEAs are characterised in PEMFCs by recording polarisation curves and Electrochemical Impedance Spectroscopy. Moreover the hydrogendiffusion current is determined.