The Paper of Prof. Tatsumi Ishihara (Principal Investigator, Hydrogen Production Research Division, I²CNER) and his collaborators was published in "Energy and Environmental Science."

■ Broader context

Perovskite-based (ABO₃) electro-ceramics have many applications
including ferroelectrics, multiferroics and electro-catalysis in high
temperature electrochemical devices. One subgroup, the A³⁺B³⁺O₃ (3,3
perovskites), are extensively used as electrode materials in solid oxide fuel
cells and electrolysers. These oxides contain a trivalent lanthanide cation
on the A-site and a mixed valence transition metal cation on the B-site,
with the lanthanide oen partially substituted by a divalent alkaline earth
to promote electrocatalysis. Their catalytic activity is oen related to the
nature of the B-site transition metal cation. Our results using a surface
analysis technique sensitive to the very outermost atomic layer show, very
unexpectedly, that the B-site transition metal cations are not exposed at
the surface to participate in catalytic reactions, to within the detection
limits of the technique. In fact, we show that for three representative
perovskite-based electro-ceramics, the larger A-site cations dominate the
surface leaving a transition metal rich region beneath the surface.
Substitution by a divalent alkaline earth cation leads to a strong preferential
segregation of this cation to the surface. These ndings indicate the
importance of characterizing the surfaces of these materials at the atomic
level for the understanding of catalytic and oxygen exchange performance.
Furthermore, they provide a basis to guide fundamental theoretical
studies of the exchange of oxygen between the gas ambient and the
electrochemically-active surfaces of perovskite-based ceramics.

■ Paper

Title: Surface termination and subsurface restructuring of perovskite-based solid oxide electrode materials

Authors: J. Druce, H. T´ellez, M. Burriel, M.D. Sharp, L.J. Fawcett, S.N. Cook, D. S. McPhail, T. Ishihara, H. H. Brongersma and J. A. Kilner