Characterisation of a Fuel Cell Membrane

Polymer Electrolyte Membranes (PEM) are applied in Solid Polymer Fuel Cells (SPFC) as a transport medium for protons. Sulfonated Polyetheretherketon (sPEEK) has been shown to be a suitable ionomer for the manufacturing of these membranes, next to Nafion.

In a series of experiments for the optimisation of the SPFCs it turned out that it didn't suffice to only take the electrolytic properties of the membranes into account. XPS was used to investigate the lack of the ionomer's conductivity. The analysis of the XPS C1s signals of an sPEEK reference and the membrane showed clear differences in the peak shapes, indicating a contamination of the membrane surface. Further investigations showed that this contamination consisted of Polyethylenterephthalate (PET). The figure shows the C1s signals of all the polymers. It is clear that PET can be recognized from the COO contribution (C5) to the signal. It was possible to calculate a PET surface coverage of 10%.

A supporting foil in the manufacturing of the sPEEK membrane was identified as the source of the PET contamination.

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