Cationic Intermixing and Reactivity at the La2Mo2O9/La0.8Sr0.2MnO3- Solid Oxide Fuel Cell Electrolyte-Cathode Interface

Among standard high-temperature cathode materials for solid oxide fuel cells, La0.8Sr0.2MnO3- (LSM) displays the least reactivity with the oxide-ion conductor La2Mo2O9 (LMO), yet a reaction is observed at high processing temperatures, identified by using XRD and focused ion beam secondary-ion mass spectrometry (FIB-SIMS) after annealing at 1050 and 1150 degrees C. Additionally, Sr and Mn solutions were deposited and annealed on LMO pellets, as well as a Mo solution on a LSM pellet. From these studies several reaction products were identified by using XRD and located by using FIB-SIMS on the surface of pelletised samples. We used depth profiling to show that the reactivity extended up to approximate to 10m from the surface region. If Sr was present, a SrMoO4-type scheelite phase was always observed as a reaction product, and if Mn was present, LaMnO3+ single crystals were observed on the surface of the LMO pellets. Additional phases such as La2MoO6 and La6MoO12 were also detected depending on the configuration and annealing temperature. Reaction mechanisms and detailed reaction formulae are proposed to explain these observations. The strongest driving force for cationic diffusion appears to originate from Mo6+ and Mn3+ cations, rather than from Sr2+.