INVITED TALK - In Situ Electronic Structure Measurements and Correlations to Reactivity on Hetero-Structures for Solid Oxide Fuel Cells

Strontium-doped lanthanum cobaltite is one of the most promising cathode candidates for intermediate temperature solid oxide fuel cells. Recently, the hetero-interfaces between the perovskite (La,Sr)CoO₃ (LSC₁₁₃) and the Ruddlesden-Popper (La,Sr)₂CoO₄ (LSC₂₁₄) phases have shown highly enhanced oxygen exchange kinetics. This observation offers the potential for a new class of cathode structure design, either via multilayering or by forming vertical heteroepitaxial nanocomposites, with high densities of these special interfaces. In this work, nanoscale multilayers and vertically aligned nanocomposites of LSC_113/214 have been prepared by pulsed laser deposition. Their surface chemistry was characterized by Auger Electron Spectroscopy with high spatial resolution, and their surface electronic structure was probed by scanning tunneling microscopy at elevated temperatures and in oxygen gas. The intimate contact of LSC₂₁₄ to the LSC₁₁₃ phase, rendered the charge transfer on the LSC₂₁₄ surface to be more facile, contributing to enhanced oxygen reduction reactivity near the LSC_113/214 interfacial regions intersecting the surface. The enhancement of the ORR kinetics is also confirmed by EIS measurement at relatively low temperatures below 400 ^oC. The surface chemistry at higher temperatures ages by time and hides the improvements that arise from the coupling of these two phases through their interface. These observations lead to a novel means for SOFC cathode fabrication with enhanced performance and provide guidelines for identifying other promising cathode candidates.