Degradation of sealings for PEFC test cells during fuel cell operation

For long-term operation of fuel cells the stability of all components is needed under extreme conditions. Especially the components in polymer electrolyte fuel cells (PEFCs) may show corrosion problems caused by the acid character of the solid electrolyte. One of the parts, which is commonly neglected, is the sealing material. Sealings are necessary for separating the gas compartments from the each other in order to avoid mixing of hydrogen and oxygen. A typical sealing material is silicone. Fuel cell components are characterized after operation in single cells under typical fuel cell conditions. After fuel cell operation frequently an alteration is visible on the sealing and the membrane parts which were in direct contact with each other. Those parts of the membrane, which were in contact with the sealing surface, became colored. Motivated by this observation membranes and sealings were investigated by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). In addition, electrodes and backings were investigated by X-ray photoelectron spectroscopy (XPS). With the XPS measurements of the electrodes operated in a silicone sealed cell, residues of the silicone were detected on its surface. This indicates that the decomposition products of the silicone seals have a high mobility. In SEM/EDX mappings, an enrichment of silicone residues on the platinum was observed. Therefore, the decomposition products may contribute to a poisoning of the catalysts and may also change the hydrophilic/hydrophobic characteristic of the electrodes.

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