| AVS 62nd International Symposium & Exhibition | |
| Applied Surface Science | Monday Sessions |
| Session AS-MoA |
| Session: | Practical Surface Analysis I: Interpretation Challenges |
| Presenter: | Aaron Geller, University of Maryland, College Park |
| Authors: | A. Geller, University of Maryland, College Park B. Eichhorn, University of Maryland, College Park |
| Correspondent: | Click to Email |
Near ambient X-ray photoelectron spectroscopy (APXPS) was used for In Operando studies on lanthanum strontium manganite (LSM, La0.8Sr0.2MnO3±∂) electrodes, one of the most popular materials currently in use on solid oxide electrochemical cells (SOCs). SOCs consisting of two LSM electrodes on a yttria-stabilized zirconia (YSZ) electrolyte were probed in an oxygen atmosphere (0.5 Torr) at ~600 oC under open circuit voltage (OCV) and polarized conditions. Polarization promotes the oxygen reduction reaction (ORR, cathodic reaction) on one LSM electrode and oxygen evolution reaction (OER, anodic reaction) on the other. Through use of an area detector, electrochemically-induced phenomena on the surface of the cell such as surface potential mapping, Sr segregation, and changes in the Mn oxidation state were observed and spatially resolved to within 20 microns.
By tracking shifts in the La 4d and Sr 3d peaks under polarization relative to OCV, local surface potentials of each LSM electrode were determined and it was observed that the majority of electrochemical activity, signified by a sharp potential drop, was located at the LSM/YSZ interface (shifts in the Zr 3d peaks were used to determine the local potential of YSZ). Several challenges in interpretation were found, the most surprising of which was a potential separation between the lanthanum and strontium components of the LSM lattice which were expected to exhibit the same potential under bias. Instead, the lattice La was driven to a higher potential than the lattice Sr on both electrodes. Furthermore, it was found that lattice Sr was relatively depleted under bias on each electrode, though the effect was more pronounced on the OER side. Sr 3d spectra also showed two different species under bias, lattice Sr and surface-segregated SrO, with the surface species shifted to a higher potential than the lattice Sr species. The data analysis process of these complex systems presented several challenges as well, which will be discussed.