Model System Supported Impedance Simulation of Composite Electrodes

Abstract

Current research on fuel electrodes of solid oxide cells (SOCs) is done either on model‐type pattern electrodes or by interpretation of impedance spectra measured on “real” porous paste electrodes. However, results obtained by both methods are not always straightforward to compare. To bridge this gap, in this study impedance spectra of 3D porous composite electrodes with a well‐defined geometry are simulated using elementary parameters from model‐type experiments. By independent variation of these elementary parameters, it is possible to analyze the influence of the individual elementary processes on the overall electrode performance without the issue of changing its microstructure, which usually occurs when changing materials in case of real porous electrodes. The obtained results identify the electrochemical reaction resistance as the parameter with the highest impact on the polarization resistance of porous electrodes. This study thus provides a basis for a knowledge‐based improvement of existing and novel composite fuel electrodes. In addition, the developed transmission line model is used for critically examining the common method of deconvolution of impedance data measured on real porous composite electrodes, which often relies on the assumption of elementary processes being represented by a serial connection of simple R||C elements.

Performance and Limitations of Nickel‐Doped Chromite Anodes in Electrolyte‐Supported Solid Oxide Fuel Cells

“…The reason for the increased resistance values is probably the thickness of the electrode being below the optimum electrochemically active thickness d opt as described in Ref. [20]. The electrode polarization resistance as a function of the electrode thickness is illustrated in the middle panel of Figure 5.…”

Excellent kinetics of single-phase Gd-doped ceria fuel electrodes in solid oxide cells

“…This circuit model was first described by Adler et al for SOFC cathodes 36 , but is also applicable for Ni-YSZ and Ni-GDC anodes 15,[37][38][39] and other porous composite electrodes 3,[40][41][42] . Here, we take the impedance model for a mixed conducting SOFC anode with finite electron and ion conductivity, which we presented previously 15,43 , and apply it to compare Ni-GDC cermet anodes with single phase GDC anodes. In both cases, the GDC surface is the active site for H 2 oxidation or water splitting 15,44,45 .…”

The Relation of Microstructure, Materials Properties and Impedance of SOFC Electrodes: A Case Study of Ni/GDC Anodes

“…The interfacial resistances and capacitances depend on the cell preparation procedure; they are likely different for symmetrical model cells, in which the electrodes are sintered on a dense electrolyte, and full SOFCs, in which the electrolyte is sputter-deposited on top of the already sintered anodes (Plansee MSC concept [3,4,7,55,56]) or co-sintered with the anodes (in typical anode supported cells). However, when the ion conducting phase in the electrode is the same as the electrolyte, e.g., Ni/YSZ [24,30,34,57] anodes or for LSM/YSZ cathodes [33], the interfacial resistance is often negligible. The impedance function of this circuit is given in Appendix A, Equations (A1) and (A2).…”

“…Only for thin electrodes with L ≤ 2λ, the ASR decreases with an increase of the electrode thickness and approaches a constant value if the thickness is further increased. More simulated impedance spectra, for which other parameters are also varied, are available in Reference [57]. Please note that the electrochemically active thickness in Reference [57] for simulated Ni/GDC cermets is much thicker, because different microstructural parameters were used.…”

“…More simulated impedance spectra, for which other parameters are also varied, are available in Reference [57]. Please note that the electrochemically active thickness in Reference [57] for simulated Ni/GDC cermets is much thicker, because different microstructural parameters were used. For simulation of the spectra, the wiring inductance, gas diffusion and interfacial effects are also neglected, and typical parameters from the Experimental Results section are chosen: Rion = 200 Ωcm, Rreact = 5 × 10 −5 Ωcm 3 and Cchem = 3000 F/cm 3 , which results in an electrochemically active thickness of 5 μm.…”