Electrochemical impedance spectroscopy of La0.6Sr0.4Co0.2Fe0.8O3-δ nanofiber cathodes for intermediate temperature-solid oxide fuel cell applications: A case study for the ‘depressed’ or ‘fractal’ Gerischer element

Abstract

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Electrochemical Impedance Spectroscopy of Electrospun La0.6Sr0.4Co0.2Fe0.8O3–δ Nanorod Cathodes for Intermediate Temperature – Solid Oxide Fuel Cells

“…Fits through the Rs‐Gd and the Rs‐RQ‐GEC are reported as well. The qualitative behavior is in excellent agreement with that reported in for continuous unbroken nanofiber electrodes. Indeed, also in the present case, at low temperature (890 K) the Nyquist plots of EIS experimental data show a single arc, which at high frequency turns into a straight line.…”

“…Frequencies between 1.0 10 5 and 1.0 10 6 Hz fall in the operating window where the error is < 1.0%, but close to the border of the operating region with error < 10.0% . The high frequency inductance of the experimental apparatus, evaluated separately as 4.9 10 −8 H , is subtracted from the raw impedance experimental data. Then, assuming that the two electrodes of the symmetrical button cell are identical, the impedance experimental data are devided by a factor 2 to obtain the impedance of the single electrode, and then they are multiplied for the electrode area (0.58 cm 2 ) in order to obtain the area specific electrode impedance, expressed in Ω cm 2 .…”

“…Following an approach proposed in a previous work , two different ECs are employed to fit the experimental EIS arcs, the first based on the ‘depressed' or ‘fractal' Gerischer, the second formed by a pure Gerischer element coupled to an RQ element. Both equivalent circuits include also a serial resistance Rs, representing the electrolyte resistance together with contact resistances, and an inductance L, due to the wires of the experimental apparatus.…”

“…Electrochemical tests, carried out carried out on symmetrical button cells through electrochemical impedance spectroscopy (EIS), demonstrated repeatability and an electrode polarization R p = 1.0–1.5 Ω cm 2 at 923 K, depending on the level of aging. In a subsequent work , further EIS tests have been presented and discussed, together with equivalent circuit (EC) modeling carried out through two different ECs. The first EC was based on the ‘depressed' or ‘fractal' Gerischer (Gd), widely used for modeling the EIS spectra obtained from MIEC electrodes , .…”

“…On the one hand, we aim at comparing the performance obtained from two LSCF electrodes with different architecture: the 3‐D stochastic nanorod structure investigated here and the unbroken nanofibers laying neatly in‐plane over the GDC electrolyte investigated previously . On the other hand, using the new set of electrochemical impedance spectroscopy (EIS) experimental data, we take the opportunity to further test and compare the previously discussed EC models .…”