Peter Khalifah, PhD , State University of New York at Stony Brook
We have migrated from exploring pyrochlore compounds with highly reduced early 3d transition metals into exploring other structures with corner-sharing octahedra which contain early 3d transition metals. We have produced the reduced titanate compounds La9Ti7O27, La5Ti4O15, and La5Ti5O17, and are currently investigating there electrochemical properties. A general challenge with the early 3d transition metals is the high temperatures needed to reduce them result in the formation of large grains.
Efforts are being made to research and install infrastructure in our lab to allow the production of these (and other) materials in nanoparticle form at high temperatures. We were also recently successful in obtaining $200K in funding to purchase a sputter deposition capable of producing these materials in the form of thin polycrystalline or epitaxial films which are very well suited for quantitative electrochemical characterization.
Aim 2: Explore hollandite compounds
Our work has broadened from covering Ti- and Ru-containing hollandites to move into Mn-containing hollandites. Although the acid stability of the Mn phases is problematic, we have begun exploring the activity of this system in basic solution with some promising initial results and are starting to explore the role of Mn valence on activity.
Substantial efforts have also been devoted to the synthesis and study of conductive Ti1-xNbxO2 rutile and rutile-related materials, which have the same 1D edge-sharing octahedral chains as hollandite compounds. These compounds have been found to have measurable but poor catalytic activity in acidic solution. However, they show no evidence of oxidation during electrochemical studies and may be promising candidates as supports for other catalysts.
Aim 3: Produce large single crystals
The focus this year has been on electrochemical testing rather than on crystal growth, so we do not have substantial new progress to report in this area.
We have additionally followed up on some recent literature reports of ORR activity in transition metal nitride materials, and have been exploring some oxynitride compounds to see if the activity and/or stability of these materials can be improved by the incorporation of oxygen into the crystal structure.