Electrode Thickness, Microstructure, and Properties of Air Electrode for High-Temperature Solid Oxide Fuel Cells, La_0.6Ca_0.4MO₃(M=Mn, Co)/YSZ

Abstract

Key factors, which determine the properties of air electrode of high-temperature solid oxide fuel cells, were studied for the La_0.6Ca_0.4MO₃(M=Mn, Co)/stabilized zirconia (YSZ)electrode system. The microstructure of the electrode was observed by SEM (Figs.1-3). Measurements were made on the complex impedance (Fig.4), and steady-state cathodic p olarization (Fig.9) of the electrodes. The results were analysed in relation to the ele ctrode thickness (Figs.5-7, 10, 11) and the following conclusions were obtained. (1) The La_0.6Ca_0.4Co₃/YSZ system prepared at 1100°C formed a CaZrO₃ layer at the interface. The l ayer works as an electrode and, consequently, the properties of this electrode is determined by the properties of the CaZrO₃/YSZ interface. (2) The cathodic reaction at the La_0.6Ca_0.4Mn₃/YSZ interface proceeds by the following 3 stages, a) the adsorption of oxygen on the surface of La_0.6Mn_0.4Co₃, b) surface diffusion of adsorbed oxygen, and c) the charge-transfer reaction at the three phase boundary of gas, La_0.6Ca_0.4Mn₃ and YSZ. Since the reaction rate of adsorption of oxygen on the La_0.6Mn_0.4Co₃ is slow, large surface area of the por ous oxide electrode is required to obtain high current density.