Untersuchungen zum Leistungs- und Korrosionsverhalten eines HT-PEM-Brennstoffzellen-Stacks

The high temperature polymere electrolyte membrane fuel cell (HT-PEM-FC) is one of the most promissing fuel cells for future use as auxiliary power unit (APU). Because of its higher working temperature the tolerance against carbon monoxide increases. This means the use of reformate gas is possible without a complex purification. But till now the HT-PEM-FC has a lower performance than the LT-PEM-FC. In addition to this disadvantage the higher temperatures, acidic surroundings and high potentials trigger a higher rate of carbon corrosion of the catalyst carrier, too. With the reaction of carbon and oxygen, carbon dioxide is set free. The catalyst loses its stability and the performance is decreasing. To investigate the carbon corrosion at different operating conditions, a mass spectrometer is used. The signal for corbon dioxide is detected. It is noted that the compressed air used to supply the stacks on the cathode side has very large variations in its carbon dioxide content. Thus, only the level of a carbon dioxide signal can be related to the base level of the compressed air. With an increasing ratio, a rising corrosion rate is asumed. For the humidification and various carbon monoxid concentrationa at the anode the signal ratio is consistend. For various cathode stoichiometries the ratio decreases with higher stoichiometry and with higher temperatures the ratio increases. In addition, it is found that the ratio also increases with lower current. Synthetic air experiments to confirm the results of anode humidification and cathode stoichiometry failed. The performance is examined by recording polarization curves. Increased humidification and increasing carbon monoxide concentration at the anode will decrease performance. By contrast, it increases at higher cathode stoichiometries and operating temperatures. It is recommended to repeat the tests with a stable carbon dioxide concentration at the cathode supply to get more reliable results.