Nonlinear Impedance Analysis of La[subscript 0.4]Sr[subscript 0.6]Co[subscript 0.2]Fe[subscript0.8]O[subscript3-[subscript[delta]] Thin film Oxygen Electrodes
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Nonlinear impedance.pdf
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Author(s)
Geary, Tim C.
Lee, Dongkyu
Shao-Horn, Yang
Adler, Stuart B.
Date Issued
July 2016
Journal
Journal of The Electrochemical Society
Publisher
Electrochemical Society
Citation
Geary, Tim C., Dongkyu Lee, Yang Shao-Horn, and Stuart B. Adler. “Nonlinear Impedance Analysis of La[subscript 0.6]Sr[subscript 0.4]Co[subscript 0.2]Fe[subscript 0.8]O[subscript 3][subscript -][delta] Thin Film Oxygen Electrodes.” Journal of The Electrochemical Society 163, no. 9 (2016): F1107–F1114.
Version
Final published version
Abstract
Linear and nonlinear electrochemical impedance spectroscopy (EIS, NLEIS) were used to study 20 nm thin film La[subscript 0.6]Sr[subscript 0.4]Co[subscript 0.2]Fe[subscript 0.8]O[subscript 3][subscript -][delta] (LSCF-6428) electrodes at 600°C in oxygen environments. LSCF films were epitaxially deposited on single crystal yttria-stabilized zirconia (YSZ) with a 5 nm gadolinium-doped ceria (GDC) protective interlayer. Impedance measurements reveal an oxygen storage capacity similar to independent thermogravimetry measurements on semi-porous pellets. However, the impedance data fail to obey a homogeneous semiconductor point-defect model. Two consistent scenarios were considered: a homogeneous film with non-ideal thermodynamics (constrained by thermogravimetry measurements), or an inhomogeneous film (constrained by a semiconductor point-defect model with a Sr maldistribution). The latter interpretation suggests that gradients in Sr composition would have to extend beyond the space-charge region of the gas-electrode interface. While there is growing evidence supporting an equilibrium Sr segregation at the LSCF surface monolayer, a long-range, non-equilibrium Sr stratification caused by electrode processing conditions offers a possible explanation for the large volume of highly reducible LSCF. Additionally, all thin films exhibited fluctuations in both linear and nonlinear impedance over the hundred-hour measurement period. This behavior is inconsistent with changes solely in the surface rate coefficient and possibly caused by variations in the surface thermodynamics over exposure time.
MIT Department
Massachusetts Institute of Technology. Department of Materials Science and Engineering
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Creative Commons Attribution 4.0 International License
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DOI of Published Version
https://doi.org/10.1149/2.0851609jes
