Insight into surface segregation and chromium deposition on La0.6Sr0.4Co0.2Fe0.8O3−δ cathodes of solid oxide fuel cells

Abstract

La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ, (LSCF) perovskite oxide is one of the most important cathode materials in the development of intermediate temperature solid oxide fuel cells (IT-SOFCs), but vulnerable to chromium deposition and poisoning in the presence of gaseous chromium species from the chromia-forming metallic interconnect. Despite extensive studies on Cr deposition on SOFC cathode materials, there is a lack of direct evidence on the surface chemistry and Cr deposition. Here, the fundamental relationship between the surface segregation and Cr deposition of LSCF cathodes is studied on dense LSCF bar samples using a dual beam high resolution focused ion beam (FIB) and a high resolution scanning electron microscope coupled with EDS. FIB-EDS mapping results clearly indicate the segregation of SrO and Co₃O₄ particles on the LSCF surface after annealing at 800 °C for 96 h. Cr deposition occurs preferentially on the segregated SrO but not on Co₃O₄. The fundamental reason for the selective and preferential Cr deposition on the segregated SrO is the exclusion effect of the presence of SrO on the reactivity between gaseous Cr species and segregated Co₃O₄, inhibiting the Cr deposition on the segregated Co₃O₄ particles.