Deposition process of Cr species at the ͑La,Sr͒͑Co,Fe͒O 3 ͑LSCF͒ electrode and Gd 0.2 Ce 0.8 O 2 ͑GDC͒ electrolyte system is investigated under the O 2 reduction conditions in the presence of a Fe-Cr alloy interconnect for solid oxide fuel cells. Deposition of Cr species preferentially occurs on the surface of the LSCF electrode with and without the cathodic polarization at 900°C, forming SrCrO 4 and Cr 2 O 3 phase. At the initial stage of the reaction, Cr deposition was not detected inside the LSCF electrode or at the LSCF electrode/GDC electrolyte interface. Deposition of Cr species on the LSCF electrode surface under the rib of Fe-Cr alloy interconnect is substantial in comparison to that under the channel of the interconnect. The results demonstrate clearly that the deposition of Cr species at the LSCF electrode is essentially a chemical reaction and is kinetically controlled by nucleation reaction between the gaseous Cr species and SrO-enriched/segregated on the LSCF electrode surface.Solid oxide fuel cells ͑SOFCs͒ are an environmentally friendly and most efficient power generation technology with very low greenhouse gas emission. The use of metals, especially chromiaforming ferrite stainless steel, as interconnect for SOFCs is desirable because of their high thermal and electronic conductivity, negligible ionic conductivity, good machinability, and low material cost. 1 However, the application of these chromia-forming alloys as interconnect poses many challenges even at reduced temperatures. The oxide scale formed on the surface of the alloy results in high electrical resistance and causes degradation of the stack performance. [2][3][4] Furthermore, under high temperatures volatile Cr species such as CrO 3 and CrO 2 ͑OH͒ 2 are generated over the oxide scale layer in oxidizing atmospheres. 5,6 It is well known that without effective protective coating, the generated gaseous Cr species generated can cause rapid performance deterioration in SOFCs due to the poisoning of the cathodes such as ͑La,Sr͒MnO 3 ͑LSM͒ for the O 2 reduction reaction. 7-10 We studied in detail the mechanism and kinetics of the deposition of Cr species at the LSM electrodes under SOFC operation conditions. 11-14 The Cr species preferentially deposit at the LSM electrode/Y 2 O 3 -ZrO 2 electrolyte interface region, forming deposit bands or rings on the yttria-stabilized zirconia ͑YSZ͒ electrolyte surface close to the edge of the LSM electrode. The deposition process is essentially dominated by the chemical dissociation of the gaseous Cr species and is most likely limited by the nucleation reaction between gaseous Cr species and nucleation agent, e.g., the manganese species ͑Mn 2+ ͒ generated under cathodic polarization or at high temperatures in the LSM electrode/zirconia electrolyte system. 12 Further study shows that the Cr deposition process strongly depends on the nature of electrode materials. 15 ͑La,Sr͒͑Co,Fe͒O 3 ͑LSCF͒ perovskite material has been extensively investigated and considered as one of the most promising cathode candidate...

The initial stages of the interaction between the Fe-Cr alloy metallic interconnect and Sr-doped LaMnO 3 (LSM) electrode of solid oxide fuel cells (SOFC) were investigated under cathodic polarization at the temperature range of 700-900°C. Cr deposits on the Y 2 O 3 -ZrO 2 (YSZ) electrolyte surface increased with the polarization time. However, it was observed that at the early stages of the reaction, there is no preferential Cr deposition at the three-phase boundary areas at the LSM electrode/YSZ electrolyte interface region. With the decrease of the temperature the Cr deposition reduced significantly, probably due to the significant reduction in the partial pressure of the gaseous Cr species and the cationic diffusivities in the LSM electrode. The results clearly demonstrated that the deposition of Cr species at the LSM electrode/YSZ electrolyte is basically a chemical reaction and kinetically controlled by the nucleation reaction between the gaseous Cr species and the Mn 2+ species generated under cathodic polarization.

No abstract

No abstract

We have shown that the Cr deposition process at ͑La,Sr͒MnO 3 ͑LSM͒ and ͑La,Sr͒͑Co,Fe͒O 3 ͑LSCF͒ cathodes of solid oxide fuel cells ͑SOFCs͒ is kinetically limited by the nucleation reaction between the gaseous Cr species and nucleation agents. In the case of the LSM electrode, the nucleation agent has been identified to be manganese species generated under cathodic polarization, and for the LSCF electrode, it is SrO species segregated at the electrode surface. Based on the mechanism proposed, we select La͑Ni,Fe͒O 3 ͑LNF͒ and ͑La,Ba͒͑Co,Fe͒O 3 ͑LBCF͒ perovskites. The results show that LNF and LBCF electrodes are highly tolerant toward the Cr deposition and are much more stable than LSM and LSCF cathodes under SOFC operating conditions in the presence of a Fe-Cr metallic interconnect.