Effect of Microstructure on the Degradation of La_0.6Sr_0.4CoO_3–δ Electrodes in Dry and Humid Atmospheres

Abstract

La0.6Sr0.4CoO3–δ electrode layers with three different microstructures were manufactured by screen‐printing, spin‐coating and infiltration into a porous Ce0.9Gd0.1O1.95 backbone. Electrode performance was monitored at 700 °C in 20% O2 over periods of 1,600 to 3,860 h by means of electrochemical impedance spectroscopy under open circuit conditions. Reference measurements were performed in dry atmospheres, where significant electrode activation was observed for cells with spin‐coated and infiltrated electrodes. Subsequently, the relative humidity level in the surrounding atmosphere was set to 30% and further raised to 60%, thus simulating SOFC operation with ambient air without pre‐drying. While no performance loss could be observed in dry atmospheres, significant degradation occurred in humid atmospheres with pronounced differences between degradation rates of half cells with different electrode microstructures. Post‐test analyses by scanning electron microscopy (SEM) and transmissionscanning electron microscopy (STEM) were employed to identify the causes for the observed differences in degradation behavior. For screen‐printed cells, the surface of the degraded electrodes was covered with small crystallites, probably consisting of SrO formed by Sr‐segregation and surface precipitation, where humidity was found to be a crucial factor. For spin‐coated and infiltrated electrodes, poisoning by impurities (Si, Cr, S) and particle coarsening were identified as potential causes.

An Efficient Bifunctional Air Electrode for Reversible Protonic Ceramic Electrochemical Cells

“…However, the presence of H 2 O, especially at high concentrations required for efficient electrolysis of water, has resulted in a rapid degradation in the catalytic activity of the-state-of-the-art air electrodes, attributed largely to waterinduced surface enrichment or segregation of the A-site cations (e.g., Sr/Ba) of the electrodes. [7][8][9] Therefore, a good air electrode for R-PCECs must also have adequate tolerance to high concentrations of H 2 O, especially in the electrolysis mode when a high concentration of H 2 O is supplied. [10] To date, considerable efforts have been devoted to the exploration of highly active and durable air electrode materials/ structures for R-PCECs.…”

Surface restructuring of a perovskite-type air electrode for reversible protonic ceramic electrochemical cells

“…The use of these double perovskite electrodes may increase the capital cost and the risk of delamination during thermal cycling. In addition, exposure to high partial pressures of steam may result in rapid degradation in the catalytic activity of these materials, due likely to the formation of Sr/Ba/Co-enriched surface or particles 12 – 14 . Therefore, a good air electrode for R-PCECs must also have sufficient tolerance against high concentrations of steam in the electrolysis mode 15 .…”

On the role of surfaces and interfaces in electrochemical performance and long-term stability of nanostructured LSC thin film electrodes

“…[6][7][8][9] However, using LSC as air electrode material in SOC cells and stacks is challenging due to the instability of its surfaces at the required operating temperatures, resulting in electrochemical performance degradation during long-term operation. 10 Several studies have shown that strontium cobaltite surfaces like LSC are prone to Sr segregation and formation of Sr-rich phases, e.g., SrSO 4 and SrCrO 4 , which result from a chemical reaction with trace impurities such as SO 2 and Cr vapors contained in the supplied air or emanating from components in the system. [10][11][12][13] A recent study has shown that the degradation on LSC surfaces already occurs from the rst exposure to ambient air and measurement conditions, indicating the effect of environmental factors on electrode stability.…”

“…10 Several studies have shown that strontium cobaltite surfaces like LSC are prone to Sr segregation and formation of Sr-rich phases, e.g., SrSO 4 and SrCrO 4 , which result from a chemical reaction with trace impurities such as SO 2 and Cr vapors contained in the supplied air or emanating from components in the system. [10][11][12][13] A recent study has shown that the degradation on LSC surfaces already occurs from the rst exposure to ambient air and measurement conditions, indicating the effect of environmental factors on electrode stability. 14 Furthermore, it has been reported that the processing and thermal history affect the long-term stability of LSC due to surface restructuring and cation redistribution.…”