Effect of Humidity in Air on Performance and Long-Term Durability of SOFCs

Anode supported SOFCs based on Ni-YSZ anodes, YSZ electrolytes, and LSM-YSZ cathodes were studied with respect to durability in humid air (similar to 4%) over typically 1500 hours. Operating temperature and current density were varied between 750 and 850 degrees C and 0.25-0.75 A/cm(2), respectively. It was found that the introduction of humidity affected the cell voltage under polarization of the cell and that this effect was (at least partly) reversible upon switching off the humidity, probably related to a segregation of impurities towards the three phase boundary in the presence of humidity. Generally, the studied cells were successfully operated in humid air under technologically relevant conditions. Improvements at the cathode/electrolyte interface made it possible to obtain highly stable cells, which can be operated under high current density and at 750 degrees C in humid air - conditions that are known to cause significant cell voltage degradation in dry air.