Interaction of La0.58Sr0.40Co0.20Fe0.80O3−δ cathode with volatile Cr in a stack test - Scanning electron microscopy and transmission electron microscopy investigations

Anode-supported solid oxide fuel cells with special thin-film yttria-stabilized zirconia electrolytes made by sol-gel technology were operated in a short stack sequentially for about 1300 h at temperatures of 700 °C and subsequently for 1200 h at 600 °C, respectively. The stack was operated galvanostatically at a constant current density of 500 mA cm−2. After operation, the stack was dismantled and the cells were analyzed with respect to Cr interaction with the LSCF cathode. Chemical analysis revealed typical overall Cr amounts of several tenths μg cm−2 cathode area depending on the operation time. SEM cross sections showed less SrCrO4 formation at the typical sites for LSCF (top side of cathode) but there was evidence of chromate formation at the border between the cathode and barrier (electrolyte) layer. This location of foreign phase formation was unexpected. Additional TEM characterizations were therefore conducted. The TEM investigation verified the presence of Cr-containing crystals and revealed pore formation in the barrier layer. The formation of SrCrO4 at this borderline and pore formation were found for the first time after SOFC stack operation.