Microanalyses of Structure, Composition, and Morphology of the Surfaces and Interfaces in LSM-Infiltrated LSCF Cathodes

The work is supported by US DOE SECA Core Technology Program under Grant No. DENT-0006557. We thank SHaRE, ORNL for TEM instrumentation and sample preparation. One of the reasons that LaxSr1−xCoyFe1−yO3−δ (LSCF) based cathodes show much better performance than those based on LaxSr1-xMnO3-δ (LSM) is that LSCF has much higher ionic and electronic conductivities than LSM, significantly extending the active sites beyond the triple-phase boundaries (TPB) [1]. One obvious downfall for LSCF is that it reacts adversely with YSZ, which can be mitigated by the use of a buffer layer of doped-CeO2 between LSCF and YSZ [2]. However, the catalytic activity of the stand-alone LSCF cathodes is likely limited by the surface catalytic properties. Further, the long-term stability of LSCF cathodes is a concern. In contrast, LSM is more chemically stable and may facilitate stronger oxygen adsorption than LSCF. Thus, it is hypothesized that the performance and stability of a porous LSCF cathode may be improved by the application of a thin coating of LSM through infiltration. Indeed, our results demonstrate that cells with a porous LSCF cathode infiltrated with a thin-film coating of LSM, SDC, and LCC displayed higher power output and better long-term stability over those without catalyst coating. However, it is not clear how the catalyst is distributed on LSCF, what the surfaces and interfaces look like, and how they evolve during annealing and operation. The objective of the study is to characterize the morphology, structure, and composition of the surfaces and interfaces in a catalyst-infiltrated LSCF cathode as prepared, after annealing under certain conditions, and after subjecting to typical fuel cell operating conditions. The microscopic information about surfaces and interfaces will then be correlated with the electrochemical behavior of the electrodes under similar conditions in order to gain critical insights into the mechanisms of performance enhancement and design of better electrodes.