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

Tuesday, May 13, 2014: 08:00
Jackson, Ground Level (Hilton Orlando Bonnet Creek)
B. Yildiz, Y. Chen, W. Ma (Laboratory for Electrochemical Interfaces, Department of Nuclear Science and Engineering, Massachusetts Institute of Technology), J. J. Kim, and H. L. Tuller (Massachusetts Institute of Technology)
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 LSC113/214 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 LSC113/214 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.