Investigation of the degradation of the hydrophobic components in low temperature fuel cell electrodes

Kurzfassung

In low temperature fuel cells gases and water must be transported into and out from the electrodes, whereby for this transport processes the hydrophobicity is important. Typically, the hydropobicity will be induced by polytetrafluoretylene. PTFE has a high chemical resistance vs. chemical reactions, but under the electrochemical conditions in fuel cells a degradation of the hydrophobicity can be observed. A loss of hydrophobicity leads to a decrease of the electrochemical performance in¬duced by the perturbation of the water balance. The loss of the hydropobicity is rela¬ted to a partial decomposition of the PTFE, which can be observed in x-ray photo¬electron spectroscopy studies. A partial loss of the hydrophobicity is observed for electrodes for different low tem¬perature fuel cells especially PTFEs and AFC. Post mortem analysis of the electro¬des and the components by XPS show that the change of the PTFE is more signifi¬cant in the anodes than in the cathodes. The alteration of the PTFE is not only an important degradation process, but also im¬portant for the start-up procedure of same electrodes; especially for the formation process of electrodes with a PTFE film on the surface. For AFC anodes as well as for a commercial type of PEFC electrodes, the alteration of the PTFE film represents the time dominating step in the start-up procedure.