Electrochemical Characterization of Complete La0.6Sr0.4Co1-XFeXO3-δ Composition Phase Space By Microelectrode Impedance Spectroscopy

Tuesday, 30 May 2017: 11:40
Grand Salon B - Section 10 (Hilton New Orleans Riverside)
C. J. Kucharczyk (California Institute of Technology), Y. Liang (University of Maryland), S. Choi (Northwestern University), X. Zhang, I. Takeuchi (University of Maryland), and S. M. Haile (Northwestern University)
Solid oxide fuel cells are a promising clean energy technology due to their high efficiency and fuel flexibility, but current commercialization efforts are limited by expensive components needed to withstand high operating temperatures [1]. Attempts to decrease operating temperature have been stymied in large part by cathode materials with high polarization resistance [2], and efforts to improve performance through composite electrode morphologies [3] lead to complex geometries that prevent rigorous comparisons between different materials. We present a case study employing a novel methodology [4] for electrode characterization that enables fundamental property determination of multiple electrode compositions and allows for rigorous performance comparisons.

In this work, the entire composition phase space of a state-of-the-art ion- and electron-conducting solid oxide fuel cell cathode material (La0.6Sr0.4Co1-xFexO3-δ) is examined with unprecedented compositional resolution (x=0 to x=1 with Δx=0.05). Gradient pulsed laser deposition was employed to obtain a compositionally graded thin film on a (100)-oriented 8 mol% Y2O3-ZrO2 electrolyte substrate. The film was patterned using photolithography and ion milling to obtain electronically isolated circular microdot electrodes ranging from 80-500 µm in diameter. Microelectrode impedance spectroscopy was performed with a robotic scanning probe in an environmental chamber to obtain relevant electrochemical parameters. The measured impedance spectra are consistent with a two-phase boundary electrochemical pathway including bulk ionic conduction through the oxide. A monotonic increase in electrochemical resistance is observed from La0.6Sr0.4CoO3–δ (LSC) to La0.6Sr0.4FeO3–δ (LSF) along with a decrease in chemical capacitance corresponding to a decrease in reducibility and oxygen vacancy concentration. This case study demonstrates the rich insights that can be gleaned from this high-throughput approach and its promising application toward searching for new high-performance solid oxide fuel cell electrode materials.

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3. Sun, C.W., R. Hui, and J. Roller, Cathode materials for solid oxide fuel cells: a review. Journal of Solid State Electrochemistry, 2010. 14(7): p. 1125-1144.

4. Usiskin, R.E., et al., Probing the reaction pathway in (La0.8Sr0.2)(0.95)MnO3+delta using libraries of thin film microelectrodes. Journal of Materials Chemistry A, 2015. 3(38): p. 19330-19345.