Characterization of electrode polarization losses in solid oxide fuel cells: Impedance spectroscopy involving spatially-limited electrode geometry

Abstract

The concept of "spatially-limited geometry" in an ionic conductor is incorporated into AC two-probe impedance spectroscopy in order to investigate the electrode-related responses of solid oxide fuel cells (SOFCs). A semispherical cylinder-shaped ionic conductor made of yttria-stabilized zirconia (YSZ) is applied to the planar electrode, and the electrical and electrochemical losses in the electrolyte and electrode are characterized. According to our study, the spatial constriction of the contact interface amplifies the electrode-related impedances, and can more efficiently separate the bulk-related impedance from the electrode polarization that is very sensitive to the microstructural features of the electrode such as size and distribution of constituent phases. In this study, the resolved bulk resistances are analyzed using the concept of "spreading resistance," whereas the resulting polarization losses in the electrolyte/electrode interface are analyzed in combination with an equivalent circuit model as a function of the resistances and constant phase elements. The present approach with spatially-limited contact impedance spectroscopy is fully explored for various electrode materials in order to confirm the validity of current methodology. (C) 2012 Elsevier Ltd. All rights reserved.