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M. Müllner:
"Oxides in Aqueous Solution: Stability and Activity at the Atomic Scale; seminartalk";
Vortrag: Seminar Institut für Allgemeine Physik (IAP), online, TU Wien; 22.12.2020.

Water electrolysis is a promising technology for the storage of surplus electric energy via its conversion to chemical energy in the form of hydrogen. This hydrogen, converted back to electricity via fuel cells, could stabilise the electricity grid, or power electric motors. An alternative to electricity-driven electrolysis would be direct, photo-driven water splitting and, in the next step, artificial photosynthesis, where solar energy is stored directly in the form of more complex, carbon containing, energy rich chemicals .
To obtain a detailed understanding of the mechanisms governing chemical reactions on surfaces, a useful approach has been to reduce the level of complexity using model systems. Studies on noble-metal single-crystal samples have laid the foundation for the field of physical electrochemistry and electrochemical surface science at the atomic level.
However, in highly oxidising conditions, such as during the oxygen evolution reaction, all metals are oxidised. This can lead to electrochemical roughening or dissolution of well-defined single-crystal surfaces and thus to a loss of atomic-level control. It is therefore reasonable to expand such investigations to well-defined metal-oxide model surfaces, which are expected to be intrinsically more stable than metals in an oxidising environment.
Here, the stability and activity of UHV prepared surfaces of single crystal oxides, including the photoactive semiconductor TiO2 and metallic oxide Fe3O4 are investigated in aqueous solution by means of electrochemical scanning tunneling microscopy (EC-STM) and ambient atomic force microscopy (AFM). The adsorption of photoactive (WO3)3 clusters, an artefact from STM tungsten tips, will also be discussed.