Combined Cr and S poisoning in solid oxide fuel cell cathodes

This work aims to compare the effect of combined chromium and sulfur contaminating conditions to the Cr contamination alone on the Cr poisoning mechanisms in (La,Sr)MnO3-(Zr,Y)O2 solid oxide fuel cell (SOFC) cathodes. Whereas Cr2O3 and (Cr,Mn)3O4 are found at active triple phase boundaries under the Cr-poisoning condition, the formation of SrCrO4 is promoted under combined Cr and S contaminating conditions, where Cr accumulations act as getters incorporating sulfur, to form Sr(Cr,S)O4 compounds. The identification of this phase is validated on the synthesized and simulated species by scanning/transmission electron microscopy (SEM/TEM) techniques; its possible formation is predicted by thermodynamic analysis of the stability of perovskite compounds in the presence of combined Cr and S polluting conditions. In contrast, sulfur alone is not found to poison active sites in these composite cathodes. These findings suggest that the Cr poisoning degradation mechanism is altered when (La,Sr)MnO3 is exposed to Cr vapors in the presence of sulfur contamination; the access to electrochemical active sites may be hindered by the formation of Sr(Cr,S)O4 in a similar manner to a Cr-getter effect in (La,Sr)(Co,Fe)O3 cathodes.

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► In combination with sulfur, the Cr-poisoning mechanism is changed in solid oxide fuel cells (SOFCs).
► Sulfur promotes the formation of Sr-chromate in Sr-doped La-manganite-based SOFC cathodes.
► Sr-chromate acts as an impurity getter and incorporates S into its structure.
► Bulky chromate phases cover less triple phase boundaries (TPB) than simple Cr oxide or Cr spinels.
► In the absence of Cr, S-poisoning does not affect active cathode TPB.