Low-temperature scanning tunneling microscopy (LT-STM) is known to be a suitable tool to investigate, at the nanometric scale, the structural and electronic properties of oxide surfaces in the form of thin films and nanostructures. Cobalt oxide nanoparticles have shown significant catalytic activity for the low temperature CO oxidation and the oxygen evolution reaction (OER) in the electrochemical water splitting. An improvement of the catalysts performance requires a controlled synthesis of the nanostructures as well as a deep understanding of the active phase and its surface chemistry. The preparation and characterization of model systems under vacuum conditions as well as a subsequent exposure to reactants under controlled conditions can be helpful in this sense. Following this methodology, CoO nanoislands supported on the Au(111) surface have been designed and employed to study the water dissociation using scanning probe and sample-average techniques. The different reported interaction of the water molecules with edge sites of the islands has been proposed to play a crucial role in the water oxidation reaction. However, an atomistic characterization of the electronic structure has been elusive. Here, we report a low temperature scanning tunneling microscopy and spectroscopy study of such a model system for water splitting. Our results show a complex structure within the oxide islands, which are characterized by a topographic and electronic Moiré, and some edge regions with distinct electronic fingerprints. In particular, the spectroscopic analysis show an increase of the valence band states at the borders of the islands and at the bottom moirons inside the nanoislands, whereas the oxygen dislocation lines have a higher density of states in the conduction band. Furthermore, a specific behavior towards water adsorption and dissociation of these sites is visualized and discussed. Thus, our study intends to open new avenues to understand and rationalized oxide nanostructures for energy related applications.

Structural and electronic characterization of CoO nanoislands on Au(111) using LT-STM

256th National Meeting (2018)

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