MSE Professors Richard Robinson and Richard Hennig Awarded a Cover Article by Journal of Physical Chemistry C
Chemical transformations of nanoparticles is a powerful method to modify the as-synthesized nanoparticle. Through these transformations the nanoparticles shape and composition can be manipulated, thereby altering the properties. However, many questions remain about the kinetics and thermodynamics of these reactions.
In this article the Robinson and Henning team examined the oxidation mechanism for cobalt nanoparticles as they transform into Kirkendall-hollowed CoO and Co3O4 particles. The nanoscale Kirkendall effect arises from asymmetric diffusion rates between two atomic components in a diffusion couple and results in hollow nanoparticles. Researchers had previously believed that the Kirkendall-hollowing was a straightforward mechanism in nanoparticles, directly related to the bulk Kirkendall effect. By using EXAFS, TEM, XRD, and DFT calculations to study the atomic structural changes and diffusion process during this transformation, the mechanism of the nanoscale Kirkendall effect is found to be more complex than previously believed: the Kirkendall hollowing is not simply due to two different diffusion rates but involves phase-related diffusion constants and processes. The O diffusion inward occurs in ?-Co in the beginning of the transformation, but the Co diffusion outward starts only when the major phase of the nanoparticles becomes CoO.
By understanding these processes the team can use these transformations to design functional nanoparticles for energy applications.
Their article, “The Oxidation of Cobalt Nanoparticles into Kirkendall-Hollowed CoO and Co3O4: the Diffusion Mechanisms and Atomic Structural Transformations”,by Don-Hyung Ha, Liane M. Moreau, Shreyas Honrao, Richard G. Hennig, and Richard D. Robinson, appears in the July 11, 2013 issue. The cover can be found at Journal Cover
And the article can be found here. Article