Investigation of the agglomeration mechanisms of the platinum catalyst in low temperature fuel cell electrodes

Kurzfassung

A sufficient life time of low temperature fuel cells cannot achieved for a lot of applications, because the electrochemical performance decreases as well as the operation behavior changes due to the operation time. For the degradation of the electrodes, which dominates the decrease of the performance and the change of the operation behavior, two different degradations processes are known: the agglomeration of the platinum catalyst and the degradation of the PTFE. The degradation of the PTFE leads to a lower hydrophobic character of the electrodes and influences the transport mechanisms resulting in a higher sensibility for the water balance. This degradation process can be partially compensated by changing of the operations conditions. However, the agglomeration of the catalysts cannot be compensated and leads to an irreversible decrease of the electrochemical performance. Therefore, it is necessary to enhance the life time of the electrodes by selecting carefully the operation conditions minimizing the degradation processes, especially the agglomeration of the platinum based catalyst. In order to find suitable operation conditions for long life times the mechanism of the agglomeration and the conditions which induces or enhances the agglomeration must be identified. For this purpose the alterations of electrodes for membrane fuel cells were investigated under various operation conditions, especially the dependence of platinum agglomeration on the humidification was investigated. High humidification and especially a liquid phase enhance the platinum agglomeration significantly.