PREPARATION OF PEROVSKITE-TYPE LA1-XSRXMNO3 FILMS BY VAPOR-PHASE PROCESSES AND THEIR ELECTROCHEMICAL PROPERTIES - II - EFFECTS OF DOPING STRONTIUM TO LAMNO3 ON THE ELECTRODE PROPERTIES

Complex alternating current impedance and steady-state polarization me asurements have been conducted on dense and thin LaMnO3 and La0.85Sr0. 15MnO3 film electrodes and porous-sintered LaMnO3 and La0.85Sr0.15MnO3 electrodes in air at elevated temperatures between 873 and 1273 K, in order to study the reaction mechanism of oxygen reduction at the La1- xSrxMnO3 electrode of a solid oxide fuel cell. By fitting impedance sp ectra to an appropriate equivalent circuit, the chemical diffusion coe fficient of oxygen and interfacial reaction resistance of the LaMnO3 a nd La0.85Sr0.15MnO3 film electrodes were determined. The chemical diff usion coefficient was scarcely affected by Sr doping, while the interf acial reaction resistance considerably decreased by Sr doping. Steady- state polarization behavior of the porous-sintered La1-xSrxMnO3 was dr amatically improved by doping Sr, while those of the dense La1-xSrxMnO 3 film were almost unchanged by Sr doping. These results suggested tha t the electrochemical reduction of oxygen at the porous La1-xSrxMnO3 e lectrode takes place around the triple phase boundary (TPB), and the r eaction rate is controlled by the surface reactions close to the tripl e phase boundary region.