Electrochemical Impedance Spectroscopy of Electrospun La_0.6Sr_0.4Co_0.2Fe_0.8O_3–δ Nanorod Cathodes for Intermediate Temperature – Solid Oxide Fuel Cells

Abstract

Electrospun La0.6Sr0.4Co0.2Fe0.8O3–δ (LSCF) nanorod cathodes are investigated. Morphological characterization shows that the nanorods are arranged into a 3‐D stochastic structure, with multiple contact points with each other. Experimental characterization of symmetrical button cells through electrochemical impedance spectroscopy demonstrates an electrode polarization resistance Rp = 3.9 Ω cm2 at 940 K and Rp = 10.9 Ω cm2 at 890 K. The impedance results, measured from 890 K up to 1,200 K, show that the depressed Gerischer behavior is not an intrinsic feature of the electrode, since it appears only at certain well defined temperatures, and then it tends to disappear for other operating temperatures. Equivalent circuit model fitting is accomplished through the depressed Gerischer element, and also through an alternative circuit based on a normal Gerischer coupled to an RQ element. The superior fitting capability of the latter equivalent circuit is demonstrated. The latter circuit allows to assess separately the impedance contribution of the electrode bulk, associated to the Gerischer element, and of the electrode/electrolyte interface, associated to the RQ element. Both the related polarization resistances are larger with the electrospun LSCF 3‐D random nanorod electrode, rather than with an electrospun LSCF electrode with unbroken nanofibers laying neatly in‐plane over the electrolyte.

An Elementary Kinetic Model for the LSCF and LSCF-CGO Electrodes of Solid Oxide Cells: Impact of Operating Conditions and Degradation on the Electrode Response

“…The evolution of the impedance diagrams at OCP are given in Fig 7a and 7b for oxygen partial pressures ranging from 0.1 to 1 atm. It can be noticed that the electrode polarization resistance significantly decreases when increasing the oxygen content, as already experimentally observed in [49,74,75]. The reaction order m was estimated fitting the experimental data with the following relation:…”

“…These reaction orders are in rather good agreement with literature data. For instance, an exponent of 0.12 was deduced for a LSCF nanorod electrode operated at 717 °C in a range of oxygen partial pressure ∈ [0.10 -0.20] atm [75].…”

Electrochemical Impedance Spectroscopy of Core‐Shell Nanofiber Cathodes, with Ce0.9Gd0.1O1.95 (Core) and Cu‐Doped La0.6Sr0.4MnO3 (Shell), for Application in Solid Oxide Fuel Cells

“…[2,13,35,39] Despite the presence of both electronic and ionic conductivity inside the core-shell nanofiber electrode, in the EIS results in Figure 5 there is no presence of Gerischer behavior which is well detected in the case of MIECs, i. e. La 1-x Sr x Co y Fe 1-y O 3-δ . [21][22][23][24]40] This can be inferred from the Nyquist plots in Figure 5, where none of the arcs shows the high-frequency line with a 45°slope typical of Gerischer behavior. In parallel, all the attempts to fit the EIS experimental data with ECs embedding a Gerischer element failed.…”

“…Indeed, LSCF and BSCF can conduct both electrons and oxygen ions extending the triple-phase-boundary (TPB) in the entire electrode volume. [8,9,[20][21][22][23][24][25] However, due to the recent geopolitical problems related to Co extraction and commercialization, Cofree materials are intensively studied. Cu is currently under investigation as a substitute.…”

Low temperature CO oxidation by doped cerium oxide electrospun fibers

“…Apart from catalysis, it is demonstrated that the electrospun copper oxide fiber can be reduced to copper fiber for transparent electrode application [11]. Going beyond simple binary oxides, La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ perovskite oxide fiber was utilized to fabricate a solid oxide fuel cell air electrode [12].…”