Impedance Studies of Symmetrical Solid Oxide Cells with LSM Electrodes and YSZ Electrolyte

Abstract

Our research focuses on understanding and improving the LSM cathode of a solid oxide fuel cell through impedance studies of symmetrical LSM/YSZ/LSM electrodes (LSM = lanthanum strontium manganite, YSZ = yttrium-stabilized zirconia). Because this system has been studied for decades, the literature is filled with impedance spectra with multiple arcs in similar symmetrical cells. The existence of multiple arcs is emphasized through deconvolution analysis (aka distribution of relaxation times) of the impedance spectra combined with equivalent circuit fitting to the impedance data. There is much speculation about the processes associated with the various arcs. Recently, we have found a solution preparation method for LSM on YSZ that yields a single arc in the impedance spectrum over a range of temperatures (600-800ºC). This behavior contrasts strongly with the multiple arcs obtained in the impedance spectra of LSM electrodes prepared in a traditional method using commercial LSM powder in a paste mixture. The impedance spectra of the two types of LSM electrodes are so distinctive that it is possible to track the impedance behavior of each electrode in a hybrid cell with a paste-based LSM electrode on one side and a solution-based LSM electrode on the other side. Two implications will be discussed: (a) the identification of the rate-determining step in the mechanism for oxygen reduction on a LSM electrode, and (b) the development of a composite LSM/YSZ cathode with an unprecedented low polarization resistance.