Chromium poisoning of LSM-YSZ SOFC cathodes - I. Detailed study of the distribution of chromium species at a porous, single-phase cathode

Detailed chemical and surface structure analyses are presented for an 8 mol % yttria-stabilized zirconia (YSZ) wafer, partially covered with a thin, porous (La0.8Sr0.2)(0.98)MnO3 (LSM) film electrode, after being cathodically poisoned in the presence of a chromia source at 800degreesC. Under the conditions used, the newly deposited Cr-containing compounds were distributed not only in and around the electroactive LSM-YSZ-air triple-phase boundary (TPB) interface region, but also extending ca. 500 mum from the edge of the LSM film onto the YSZ surface. The distribution and structure of the Cr species on the YSZ surface was directly correlated with variations in the cathodic polarization of the half-cell for a solid oxide fuel cell (SOFC). Such structuring was not anticipated, considering that the electrochemical activity is thought to occur only at the LSM-YSZ-air TPB. Evidence presented here suggests that Cr2O3 plays an important role in extending the electroactive LSM-YSZ-air TPB out onto the YSZ surface by effectively creating a new Cr2O3-YSZ-air TPB region. (C) 2004 The Electrochemical Society.