Preparation and Characterization of Highly Stable Ionomers and Ionomer Membranes for Medium Temperature Fuel Cells

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In this proposal a fundamental approach for highly stable fuel cell membranes and membrane-electrode assemblies is intended. As a first step, sulfonated aromatic monomers and model compounds additionally modified with different electron-withdrawing and therefore sulfonic acid-stabilizing groups will be synthesized and investigated in terms of their stability using different methods like thermogravimetry (TGA)-FTIR-coupling experiment (thermal stability, identification of thermal decomposition products); electron spin resonance (ESR) (radical attack stability); cyclovoltammetry (electrochemical stability); storage in water, aqueous acid, aqueous base, aqueous oxidants (stability in these solvents, readable from the change in ion-exchange capacity after storage). In a second step, the selected monomers with the highest stabilities will be polymerised via suitable methods (nucleophilic displacement polymerisation and other polycondensations, Suzuki coupling, etc.), and also investigated in terms of their stability. As a third step, membranes of the novel polymers will be prepared. These membranes can also be additionally cross-linked via known methods to limit water-uptake. Moreover the membranes will optionally be doped with inorganic compounds to improve their water storage ability, proton conductivity at T more than 100°C, and their thermal stability. The membranes will also be characterized in terms of their thermal and (electro)chemical stability via the methods available in the labs of the project partners. As a fourth step, from the membranes showing the best thermal and (electro)chemical stabilities membrane-electrode assemblies will be prepared, also using catalysts and electrodes prepared by the respective project partners, and will be characterized and tested in both PEFC and DMFC. One important aspect of the project is the investigation of the electrodeelectrolyte interface and the function and properties of the polymeric ionomers at this interface. The goal of these investigations is to enable a more rational improvement of the electrode, in particular electrodes with poly-arylene-based ionomer components from the ICVT. Different new strategies to obtain insight into the processes of the catalytically active layer of the polymer electrolyte fuel cells (PEFCs) are to be developed.