Characterization of a LSCF/GDC Cathode Composite in Solid Oxide Fuel Cells Using Impedance Spectroscopy

Abstract

A composite cathode of LSCF(La0.6Sr0.4Co0.2Fe0.8O3) and GDC(Gd2O3-Doped CeO2: Cd0.9Ge0.1O1.95) was characterized in terms of an electrode response, using a point contact in an yttria-stabilized zirconia (YSZ) electrolyte incorporated into AC two-point impedance spectroscopy. The point-contacted configuration amplifies the responses occurring near the YSZ/cathode interface through the aligned point contact on the planar LSCF/GDC electrode. The point contact interface increases the bulk resistance allowing the estimation of the point contact geometry and resolving the electrode-related responses. The resultant impedance spectra are analyzed through an equivalent circuit model constructed by resistors and constant phase elements. The bulk responses can be resolved from the electrode-related portions in terms of spreading resistance. The electrode-related polarizations are measured in terms of temperature and oxygen partial pressure. The modified impedance spectroscopy is discussed in terms of methodology and analytical aspects, toward resolving the electrode-polarization issues of solid oxide fuel cells.