The Oxidation of Cobalt Nanoparticles into Kirkendall-Hollowed CoO and Co3O4: The Diffusion Mechanisms and Atomic Structural Transformations
- Authors
- Ha, Don-Hyung; Moreau, Liane M.; Honrao, Shreyas; Hennig, Richard G.; Robinson, Richard D.
- Issue Date
- Jul-2013
- Publisher
- AMER CHEMICAL SOC
- Citation
- JOURNAL OF PHYSICAL CHEMISTRY C, v.117, no.27, pp 14303 - 14312
- Pages
- 10
- Journal Title
- JOURNAL OF PHYSICAL CHEMISTRY C
- Volume
- 117
- Number
- 27
- Start Page
- 14303
- End Page
- 14312
- URI
- https://scholarworks.bwise.kr/cau/handle/2019.sw.cau/54143
- DOI
- 10.1021/jp402939e
- ISSN
- 1932-7447
1932-7455
- Abstract
- We report on the atomic structural changes and diffusion processes during the chemical transformation of epsilon-Co nanoparticles (NPs) through oxidation in air into hollow CoO NPs and then Co3O4 NPs. Through XAS, XRD, TEM, and DFT calculations, the mechanisms of the transformation from epsilon-Co to CoO to Co3O4 are investigated. Our DFT calculations and experimental results suggest that a two-step diffusion process is responsible for the Kirkendall hollowing of epsilon-Co into CoO NPs. This first step is O in-diffusion by an indirect exchange mechanism through interstitial O and vacancies of type I Co sites of the epsilon-Co phase. This indirect exchange mechanism of O has a lower energy barrier than a vacancy-mediated diffusion of O through type I sites. When to CoO phase is established, the Co then diffuses outward faster than the O diffuses inward, resulting in a hollow NP. The lattice orientations during the transformation show preferential orderings after the single-crystalline. epsilon-Co NPs are transformed to polycrystalline CoO and Co3O4 NPs. Our Co3O4 NPs possess a high ratio of {110} surface planes, which are known to have favorable catalytic activity. The Co3O4 NPs can be redispersed in an organic solvent by adding surfactants, thus rendering a method to create solution-processable colloidal, monodisperse Co3O4 NPs.
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