Evidence for Two Activation Mechanisms in LSM SOFC Cathodes

Dense La 0.8 Sr 0.2 MnO 3 (LSM) film electrodes with an average thickness of 600 nm were fabricated on yttria-stabilized zirconia and cerium gadolinium oxide by ultrasonic spray pyrolysis. LSM was studied for initial nonstationary behavior by activating with current density for short duration (5 min) and long duration (16 h). The polarization resistance at zero dc bias was reduced upon activation irrespective of the electrolyte, with the reduction more significant after long-duration activation. Short-duration activation was removed by deliberate introduction of La 2 Zr 2 O 7 impurities into the LSM phase or by surface doping with La 0.6 Sr 0.4 FeO 3 nanoparticles. However, long-duration activation still occurred in these samples. Scanning electron micrographs of short-duration-activated films showed no changes in morphology while long-duration activation resulted in a significant bulk pore formation in the LSM phase. Two distinct mechanisms for LSM activation in a solid oxide fuel cell (SOFC) are proposed. Short-duration activation results in changes in the film surface chemistry while long-duration activation leads to the reconstruction of the LSM phase.