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

Abstract

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. 1. Yang, Z.G., Recent advances in metallic interconnects for solid oxide fuel cells. International Materials Reviews, 2008. 53(1): p. 39-54. 2. Kuklja, M.M., et al., Combined theoretical and experimental analysis of processes determining cathode performance in solid oxide fuel cells. Physical Chemistry Chemical Physics, 2013. 15(15): p. 5443-5471. 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.