Journal
JOURNAL OF MATERIALS CHEMISTRY A
Volume 6, Issue 14, Pages 5703-5713Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/c8ta00265g
Keywords
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Funding
- Austrian Science Fund (FWF)
- ERC Advanced Grant OxideSurfaces
- Vienna Scientific Cluster (VSC)
- U.S. Department of Energy under EPSCoR [DE-SC0012432]
- Louisiana Board of Regents
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Activating the O-2 molecule is at the heart of a variety of technological applications, most prominently in energy conversion schemes including solid oxide fuel cells, electrolysis, and catalysis. Perovskite oxides, both traditionally-used and novel formulations, are the prime candidates in established and emerging energy devices. This work shows that the as-cleaved and unmodified CaO-terminated (001) surface of Ca3Ru2O7, a Ruddlesden-Popper perovskite, supports a full monolayer of superoxide ions, O-2(-),when exposed to molecular O-2. The electrons for activating the molecule are transferred from the subsurface RuO2 layer. Theoretical calculations using both, density functional theory (DFT) and more accurate methods (RPA), predict the adsorption of O-2(-) with E-ads = 0.72 eV and provide a thorough analysis of the charge transfer. Non-contact atomic force microscopy (nc-AFM) and scanning tunnelling microscopy (STM) are used to resolve single molecules and confirm the predicted adsorption structures. Local contact potential difference (LCPD) and X-ray photoelectron spectroscopy (XPS) measurements on the full monolayer of O-2(-) confirm the negative charge state of the molecules. The present study reports the rare case of an oxide surface without dopants, defects, or low-coordinated sites readily activating molecular O-2.
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