The relation of surface chemistry and surface electronic structure to oxygen reduction reaction (ORR) kinetics remains an outstanding question to this day in the search for highly active cathodes for SOFCs. It has been possible to control the bulk magnetic and electronic properties of perovskite thin films by manipulating their lattice parameters with different growth conditions, hydrostatic pressure, or use of substrates with a different lattice mismatch to the films. Furthermore, impact of the lattice strain on the surface electronic structure and reactivity has been long demonstrated for low temperature noble metal electrocatalysts. On the other hand, the role of lattice strain on the surface cation and anion chemistry, electronic structure and ionic transport, which all influence the ORR activity of SOFC-related oxides, is attracting its due interest only recently.
The goal in this research is to uncover and control how lattice strain couples to the oxygen vacancy formation and diffusion, oxygen surface adsorption, inherent electronic structure, and dopant segregation on the surface of perovskite-type cathodes. For this purpose, we integrate surface chemistry and electronic structure measurements on nanoscale thin film electrodes, using x-ray photoelectron spectroscopy and scanning tunneling spectroscopy, with first principles-based predictive simulations. The model cathode materials that we investigate are based on LaxSr1-xCoO3 thin films with controlled crystallography.