Oxygen reaction on strontium-doped lanthanum cobaltite dense electrodes at intermediate temperatures

Abstract

La 0.7Sr 0.3CoO 3− δ (LSC) powder was characterized by thermogravimetry. Thin, dense layers of LSC were deposited by RF magnetron sputtering on YSZ pellets. The electrochemical behavior was studied as functions of temperature (300–530°C) and oxygen partial pressure (0.21–2×10 −5 bar) by impedance spectroscopy. Impedance diagrams were decomposed into two elements, characteristic of the electrode polarization. The low frequency contribution can be described either as a limiting Warburg diffusion loop or as a semi-circle. These results can be interpreted in terms of a progressive evolution of the limiting process as functions of oxygen pressure and temperature, i.e. a finite diffusion process in series with dissociative sorption process. Under low oxygen pressure, at temperatures higher than 475°C, gas-phase diffusion polarization becomes significant.