Chromium Poisoning Effects on Surface Exchange Kinetics of La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ

Abstract

The presence of Cr has already been reported in literature to cause severe degradation to LaSrCoFeO (LSCF). However, fundamental understanding of Cr effects on the surface exchange kinetics is still lacking. For the first time, in situ gas phase isotopic oxygen exchange was utilized to quantitatively determine Cr effect on oxygen exchange kinetics of LSCF powder as a function of temperature and water vapor. Our investigations revealed that the formation of secondary phases such as SrCrO, CrO, Cr-Co-Fe-O, and La-Co-Fe-O can affect both the oxygen dissociation step and overall surface exchange. Specifically, Cr-containing secondary phases on the surface not only decrease the active sites for surface reactions but also alter the nearby stoichiometry of the LSCF matrix, thereby limiting surface oxygen transport. In addition, water molecules actively participate in the surface reactions and can further block the active sites.

Enhancing Oxygen Reduction Activity and Cr Tolerance of Solid Oxide Fuel Cell Cathodes by a Multiphase Catalyst Coating

“…For the bare LSCF cathode, Sr–O segregations (in the form of Sr[OH] 2 in humidified air) on the LSCF surface readily react with Cr species (e.g., CrO 3 and Cr[O 2 H] 2 ) to form inert SrCrO 4 , which is detrimental to the ORR activity. [ 18 ] Reaction energies of these reactions (S1–S3, Table 1) are between −120.5 and −87 kJ mol −1 . As for the MP catalyst‐coated cathode, the LSCF surface is covered by BCFN and BaCO 3 phases.…”

“…[ 14–16 ] These inert secondary phases on the surface of LSCF disrupt electron conduction as well as surface oxygen transport and dissociation, resulting in an increase in Ohmic resistance and a decrease in electrocatalytic activity for the oxygen reduction reaction (ORR). [ 17–19 ] The Sr segregation and Cr‐poisoning effect will be significantly exacerbated by the presence of H 2 O. [ 20–23 ]…”

“…[14][15][16] These inert secondary phases on the surface of LSCF disrupt electron conduction as well as surface oxygen transport and dissociation, resulting in an increase in Ohmic resistance and a decrease in electrocatalytic activity for the oxygen reduction reaction (ORR). [17][18][19] The Sr segregation and Cr-poisoning effect will be significantly exacerbated by the presence of H 2 O. [20][21][22][23] Surface modification with catalyst coatings has been demonstrated as an effective strategy to enhance the ORR activity and contaminant tolerance of cathodes.…”

High performance nanostructured bismuth oxide–cobaltite as a durable oxygen electrode for reversible solid oxide cells

“…However, the surface segregation of Sr-containing cobaltite oxygen electrodes and the combination of segregated Sr with volatile species such as chromium and sulphur constitute a major degradation mechanism of SOC stacks. [10][11][12][13][14][15][16][17] One straightforward means to address this critical issue is to develop Sr-free cobaltite electrodes, 18 such as La(Co,Fe) x Pd 1Àx O 3Àd . 19,20 Recently, we have successfully developed a high performance Sr-free Sm 0.95 CoO 3Àd electrode doped with 5% Pd in the B-site of the perovskite structure (SmCPd) and assembled it on a barrier-layer-free Y 2 O 3 -ZrO 2 (YSZ) electrolyte.…”

Evaluation of BaCo0.4Fe0.4Zr0.2−xNixO3−δ perovskite cathode using nickel as a sintering aid for IT-SOFC

“…Composition (x ¼ 0) shows the least dense structure while composition (x ¼ 0.04) shows the most dense structure. It can be deduced from SEM micrographs that pores reduced because nickel melted during sintering and diffused into the lattice of host Zr 4+ , and it also acted as a sintering aid due to its high surface energy 26. The increased concentration of Ni in BaCo 0 .…”