Effect of angstrom-level oxide overcoat on Sr segregation behavior of LSM electrodes

Long-term durability of perovskite (ABO3)-based cathodes in solid oxide fuel cells has been largely limited by surface segregation of A-site dopant and thermal agglomeration. Since a deposition of an atomically thin oxide has proven to be highly effective in suppressing electrode agglomeration, a successful suppression of dopant segregation with the same approach will enhance the durability of cathodes significantly by killing two birds with one stone. In this report, we demonstrate that an atomic-scale overcoat with a nominal thickness of 2–3 Å is indeed an effective approach of tuning Sr segregation behavior in La0.8Sr0.2MnO3 (LSM) if a proper choice of the overcoat material is made. Coating of a binary oxide with multi-valent cations (CeO2 and TiO2) desegregates Sr species into the lattice of LSM while an overcoat with single valent cations (ZrO2 and Y2O3) exhibits little effect on Sr segregation. A mechanistic interpretation of the behavior is also presented based upon a series of X-ray photoelectron spectroscopy and electrochemical analyses.