Journal
SURFACE SCIENCE
Volume 668, Issue -, Pages 93-99Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.susc.2017.10.018
Keywords
Layered structure; Delafossite oxide; Thin film; Atomic scattering spectroscopy; X-ray absorption spectroscopy; Density functional theoretical calculations
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Funding
- RIKEN Advanced Institute for Computational Science through the HPCI System Research Project [hp140247]
- Grants-in-Aid for Scientific Research [15H05500] Funding Source: KAKEN
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Delafossite oxides (ABO(2)) have a layered structure with alternating layers of A and B elements, the topmost layer of which appears to determine their performance, such as the oxygen evolution reaction (OER) activity. In this study, we investigated the topmost layer of single-domain (0 0 1)-oriented AgCoO2 epitaxial thin film for potential use as an OER catalyst. The thin film was confirmed to possess OER activity at a level comparable to the catalyst in powder form. Atomic scattering spectroscopy revealed the topmost layer to be composed of CoO6 octahedra. In situ X-ray absorption spectroscopy showed that the oxidation of Co at the surface did not change under different potentials, which suggests that there is no valence fluctuation of Co in the stable CoO6 octahedral structure. However, the oxidation number of Co at the surface was lower than that in the bulk. Our density functional theoretical calculations also showed the Co atoms at the surface to have a slightly higher electron occupancy than those in the bulk, and suggests that the unoccupied t(2g) states of Co at the surface have an influence on OER activity. (C) 2017 Elsevier B.V. All rights reserved.
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