Effect of Cation Demixing on the Electrochemical Performance of LSCFO Cathodes for SOFCs

BAQUÉ, LAURA; SOLDATI, ANALIA L.; TROIANI, HORACIO; SERQUIS, ADRIANA C.

ECS Transactions

Electrochemical Society

Lugar: Pennington; Año: 2014 vol. 64 p. 11 - 16

1938-6737

The commercialization of Solid oxide fuel cells (SOFCs) is stillhindered by their cost and long term degradation. One of thecommon degradation mechanisms of La1-xSrxFe1-yCoyO3-d(LSCFO) cathodes reported in literature is element demixing. Inthis work, the degradation of LSCFO cathodes deposited on Ce1-xGdxO2-d electrolytes at 800°C in air for 50 h was investigated byelectrochemical impedance spectroscopy (EIS), scanning electronmicroscopy (SEM) and transmission electron microscopy (TEM).EIS spectra from LSCFO cathodes present two contributions: oneat high frequency and another at low frequency. The highfrequency contribution remains invariable during the ageingtreatment while the low frequency contribution continuouslyincreases. The formation of small segregates was observed afterthe ageing treatment. Energy dispersive spectroscopy analysisreveals that these segregates were particularly poor in Sr.IntroductionHydrogen along with renewable energy resources are planned to replace fossil fuels inthe near future. Solid oxide fuel cells (SOFCs) are an attractive solution for the transitionperiod between both energy sources since they can operate by using not only hydrogenbut also fossil fuels (1,2). Nevertheless, the commercialization of these devices is stillhindered by their cost and long term degradation. Overall cell degradation depends on thedegradation mechanisms of its main components: anode, electrolyte and cathode.The use of mixed conducting cathodes such as La1-xSrxFe1-yCoyO3-d (LSCFO)improves considerably the performance of the cell. However, one of the most commondegradation mechanisms of LSCFO cathodes reported in the literature is elementdemixing and, particularly, Sr segregation. Although Sr segregation is usually reported inliterature as a degradation mechanism responsible for the deterioration of the cathodeperformance, it is rarely seen as precipitates themselves. It is generally detected by anincrease in the Sr content in some zones, mostly at the surface of the sample. However,Oh et al. (3) has actually observed Sr-rich precipitates in dense LSCFO samples but theydid not reported how these precipitates affect the cathode electrochemical performance.The aim of this work is to study the effect of ageing on the electrochemicalperformance of