Chromate formation at the interface between a solid oxide fuel cell sealing glass and interconnect alloy

The presence of both chromium and sulfur (Cr/S) contaminants on the microstructure and electrocatalytic activity properties of La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) electrodes of solid oxide fuel cells (SOFCs) is studied, using Confocal laser Raman spectroscopy, XRD, scanning electron microscopy, X-ray photoelectron spectroscopy (XPS) and electrical conductivity relaxation (ECR) methods. LSCF dense bar samples were heat treated in the presence of Cr 2 O 3 and 20 ppm SO 2 and in the temperature range of 600-900 • C. The deposition and reaction products between LSCF and Cr/S depend on the temperature: SrCrO 4 only forms on LSCF samples at 900 • C and 800 • C, while formation of SrSO 4 phase occurs at all temperatures studied. The results indicate that sulfur shows a higher activity with LSCF, as compared to gaseous Cr species. Segregated SrO is more likely to react with gaseous Cr species at higher temperatures, however, reaction with SO 2 is more pronounced at lower temperatures, forming SrSO 4 . ECR results indicate that co-deposition of Cr and sulfur significantly deteriorates the surface exchange and diffusion processes for the O 2 reduction reaction on LSCF electrodes. The durability of a solid oxide fuel cell (SOFC) is critically related to the degradation behavior of its cathodes such as La 0.8 Sr 0.2 MnO 3 (LSM) and La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) in the presence of impurity species such as chromium from the chromia-forming interconnect, silica, boron and volatile alkaline elements from the glass seals sealant and sulfur from air.1-8 Among them, gaseous chromium species vaporized from the chromium oxide scale of chromia-forming metallic interconnect are probably the most investigated contaminants affecting the performance of SOFCs' cathodes. The mechanism and process of the deposition and poisoning of chromium species at the cathodes of SOFCs have been extensively investigated, including LSM, 9-11 LSCF 12 and Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ (BSCF). 13 In the case of LSCF electrodes, deposition of Cr species preferentially take place on the surface of the LSCF electrode, resulted from the interaction between the segregated SrO and gaseous Cr species.14,15 Both the humidity in the air stream and operation temperature have a significant effect on the Cr deposition. 16 Cr deposition decreases significantly with the decrease of temperature, most likely due to the reduced Sr segregation as well as the decrease of the partial pressure of gaseous Cr species at reduced temperatures. 17The sulfur in the form of SO 2 or H 2 S in the air stream is another important contaminant affecting the performance stability of SOFC cathodes. SO 2 content in air can be in the range of 10-340 μg m −3 (3.5 × 10 −3 -0.12 ppm) in cities. 18 Despite the low concentration of SO 2 , sulfur in the air stream can accumulate at the cathodes of SOFC cells, degrading the performance.5 Wang et al. 19 studied the polarization performance behavior of LSCF in the presence of 0.1 ppm SO 2 and observed two-stages of performance degrad...

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“…• C and can be identified as the formation of SrCrO 4 phase, 24 while for the sample heat treated at 700…”

Section: Resultsmentioning

confidence: 99%

Co-Deposition and Poisoning of Chromium and Sulfur Contaminants on La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δCathodes of Solid Oxide Fuel Cells

Wang

O’Donnell

et al. 2015

J. Electrochem. Soc.

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“…Considering the redox characteristic of the interfacial reaction (e.g., SrO þ 0.5Cr 2 O 3 þ 0.75O 2 ¼ SrCrO 4 ) [7], ions with different valence states, such as Mn, Fe and Ce, in glasses might act as a competitive reaction for the interfacial reaction, by consuming the oxygen at the triple-phase boundary (TPB). In this paper, MnO 2 is added gradually, from 2 to 10 mol %, to a representative Sr-containing borosilicate sealing glass.…”

Section: Introductionmentioning

confidence: 99%

Controlling the redox reaction at the interface between sealing glasses and Cr-containing interconnect: Effect of competitive reaction

Chen

Lin

Yang

et al. 2014

Journal of Power Sources

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“…For example, the Gibbs energy change of reaction (1) at 800 C on the anode (in forming gas, PO 2 ¼ 10 À16 atm) and cathode side (in air, PO 2 ¼ 0.2 atm) are 105 and À133 kJ mol À1 , respectively. Therefore, thermodynamic studies on the interfacial reaction of SOFC have been focused on the cathode side (in air) [19]. The Gibbs energy changes for possible reactions on the cathode side (in air) were then calculated as a function of temperature, as shown in Fig.…”

Section: Resultsmentioning

confidence: 99%

Improving the chemical compatibility of sealing glass for solid oxide fuel cells: Blocking the reactive species by controlled crystallization

Zhang

Zou

Fan-rong

et al. 2012

Journal of Power Sources

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Chromate formation at the interface between a solid oxide fuel cell sealing glass and interconnect alloy

Cited by 53 publications

References 19 publications

Co-Deposition and Poisoning of Chromium and Sulfur Contaminants on La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δCathodes of Solid Oxide Fuel Cells

Co-Deposition and Poisoning of Chromium and Sulfur Contaminants on La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δCathodes of Solid Oxide Fuel Cells

Controlling the redox reaction at the interface between sealing glasses and Cr-containing interconnect: Effect of competitive reaction

Improving the chemical compatibility of sealing glass for solid oxide fuel cells: Blocking the reactive species by controlled crystallization

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Chromate formation at the interface between a solid oxide fuel cell sealing glass and interconnect alloy

Cited by 53 publications

References 19 publications

Co-Deposition and Poisoning of Chromium and Sulfur Contaminants on La0.6Sr0.4Co0.2Fe0.8O3-δCathodes of Solid Oxide Fuel Cells

Co-Deposition and Poisoning of Chromium and Sulfur Contaminants on La0.6Sr0.4Co0.2Fe0.8O3-δCathodes of Solid Oxide Fuel Cells

Controlling the redox reaction at the interface between sealing glasses and Cr-containing interconnect: Effect of competitive reaction

Improving the chemical compatibility of sealing glass for solid oxide fuel cells: Blocking the reactive species by controlled crystallization

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Co-Deposition and Poisoning of Chromium and Sulfur Contaminants on La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δCathodes of Solid Oxide Fuel Cells

Co-Deposition and Poisoning of Chromium and Sulfur Contaminants on La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δCathodes of Solid Oxide Fuel Cells