Degradation mechanism of electrolyte and air electrode in solid oxide electrolysis cells operating at high polarization

Title
Degradation mechanism of electrolyte and air electrode in solid oxide electrolysis cells operating at high polarization
Authors
김정희지호일다사리하리신동욱송휴섭이종호김병국제해준이해원윤경중
Keywords
solid oxide electrolyzer; impedance spectroscopy; anodic current; degradation; densification
Issue Date
2013-02
Publisher
International journal of hydrogen energy
Citation
VOL 38, NO 3, 1225-1235
Abstract
Degradation mechanism of the electrolyte and air electrode is reported for solid oxide electrolysis cells (SOECs). Symmetric cells composed of yttria-stabilized zirconia (YSZ) electrolyte, Sr-doped LaMnO3±δ (LSM)/YSZ composite working and counter electrodes, and Pt ring-type reference electrode are used to simulate the operating conditions of the air electrode. Degradation behavior in the impedance spectra is characterized as growth of mid-frequency arc at the initial stage, gradual increase of ohmic resistance throughout the operation, and sharp rise of low frequency resistance at the final stage, followed by catastrophic cell failure. Initial stage degradation is attributed to deactivation of LSM, resulting from reduction of oxygen vacancy concentration and/or segregation of passivation species on LSM surface under anodic current passage. Intergranular fracture, which occurs along the grain boundaries of the YSZ electrolyte, is responsible for gradual increase of ohmic resistance. Increase of low frequency arc at the final stage is caused by densification of the air electrode, leading to excessive pressure build-up and delamination of the air electrode. Cation migration, which is facilitated by oxygen excess nonstoichiometry of LSM and externally applied electric field, is considered to be the main cause of permanent damages.
URI
http://pubs.kist.re.kr/handle/201004/44397
ISSN
03603199
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KIST Publication > Article
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