Measuring Electrical Properties of Thin Film Fuel Cell Electrodes by In Situ Infrared Spectroscopy

摘要

The mixed conducting perovskites (ABO_3) containing rare and alkaline earth metals on the A-site and a transition metal on the B-site are commonly used as cathodes for solid oxide fuel cells (SOFC).[1-4] To measure their electrical conductivity is very important to understand their electrochemical properties. Although the bulk electrical conductivity (specific conductance) of perovskite oxides has been intensively studied as a function of temperature or oxygen partial pressure (P_(02)),[5-8] in situ measurements of the conductivity of these materials in contact with the electrolyte as in a SOFC configuration have hardly been reported. To measure the in-plane conductivity of an electrode film on the electrolyte, a substrate with high resistance would be required for diminishing the leakage current through the substrate. Therefore, it is particularly difficult to measure the conductivity of electrodes on the electrolyte in a wide range of temperature since the electrolyte becomes highly conductive at high temperature. In addition, it is also hardly possible to reliably measure the (local) conductivity of films with insulating inhomogeneities such as pores or cracks by electrical methods. In this study, we report the electrical conductivity of perovskite La_0.6Sr_0. 4CoO_(3_δ) (LSC) thin films on yttria-stabilized zirconia (YSZ) electrolyte quantitatively obtained by in situ infrared (IR) spectroscopy. This method enables a reliable measurement of the electronic conductivity of the electrodes as part of the SOFC configuration regardless of leakage current through the substrate and cracks in the film, and avoids the necessity of preparing ohmic contacts to the film. We also show that IR spectra with applied external bias on the LSC film enable to determine the electrical conductivity of the film in the wide range of effective oxygen partial pressures.