Deposition of chromium species at Sr-doped LaMnO3 electrodes in solid oxide fuel cells I.: Mechanism and kinetics

Deposition processes of chromium (Cr) species for the system chromia-forming alloy metallic interconnect/Sr-doped LaMnO3 (LSM) electrode/3 mol % Y2O3-ZrO2 (TZ3Y) electrolyte have been investigated under various conditions at 900 degreesC. Deposition of Cr species preferentially occurred on the zirconia electrolyte surface under both cathodic (O-2 reduction) and anodic (O-2 oxidation) polarization, and formed deposit rings at the edge of the LSM electrode. The deposit ring was ca. 60 mum wide after cathodic polar polarization for 50 h and ca. 89 mum for 129 h. Cr was not detected on the surface of the LSM electrode or inside the electrode body under the conditions studied. In the absence of polarization potentials, Cr deposits were also found on the zirconia electrolyte sur face heated at 1100 degreesC but not at 900 degreesC. In all cases, energy despersive spectrometry analysis indicated that deposits mainly consisted of Cr and/or Cr-Mn, indicating the formation of Cr2O3 and (Cr,Mn)(3)O-4-type spinel phases. The results clearly demonstrated that the deposition of Cr species at the LSM electrode/TZ3Y electrolyte is not dominated by electrochemical reduction of high valent Cr vapor species to Cr2O3 in competition with O-2 reduction. The driving force for the Cr deposition processes is most likely related to the Mn species, in particular the Mn2+ ions, generated under polarization potentials or at high temperatures. The proposed deposition mechanism is consistent with the electrochemical behavior of LSM electrodes in the presence of chromia-forming alloy interconnect. (C) 2000 The Electrochemical Society. S0013-4651(99)10-037-5. All rights reserved.