Self-assembled nanocomposite cathode materials for Solid Oxide Fuel Cells

S. Stämmler, R. Merkle

Hetero-interfaces have been shown to exhibit peculiar properties, e.g. ionic conductivity or lithium storage ability, which can exceed that of the individual phases by orders of magnitude.

In the present project we investigate if hetero-interfaces, e.g. between perovskite (La,Sr)CoO_3-δ and Ruddlesden-Popper phase (La,Sr)₂CoO_4+δ, have a significant effects on the oxygen exchange reaction. Self-assembled twp-phase films on YSZ are prepared by pulsed laser deposition from a single target. In the crastallization process, the deposited material deparates into the two phases, with a crystallite size of about 50 nm. Typical film morphologies are shown below.

In the crystallization process, the two phases acquire a different Sr content. As proven by analysis of the lattice constants and TEM-EDX, the perovskite phase becomes depleted in Sr which strongly decreases its oxygen exchange activity, while the activity of the Ruddlesden-Popper phase is hardly affected by the increased Sr concentration. This has to be considered when conparing the oxygen reduction activity (measured by impedance spectroscopy on microelectrodes) of single-phase with two-phase films.

Publications:

S. Stämmler, R. Merkle, B. Stuhlhofer, G. Logvenov, and J. Maier 
Influence of Hetero Grain Boundaries on Oxygen Exchange Activity: Investigation of Two-phase (La,Sr)CoO_3-δ /(La,Sr)₂CoO_4+δ Cathode Materials 
ECS Transactions, accepted, 2015.