Oxides in aqueous solution: stability and activity at the atomic level

This thesis is an electrochemical surface science study of oxides in aqueous solution. Stability and activity of model systems is studied at the atomic scale, with a focus on scanning probe microscopy in ambient atmosphere and liquid.Single crystal surfaces are prepared in ultra high vacuum and characterised with scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), X- ray photoelectron spectroscopy (XPS) and low-energy ion spectroscopy (LEIS). Elec- trochemical methods include cyclic voltammetry (CV) and impedance spectroscopy. Stability in liquid electrolyte is studied with electrochemical STM (EC-STM). The surfaces are post characterised by atomic force microscopy (AFM) at ambient conditions and STM, LEED and XPS in UHV.Complexity and technological relevance of the studied model systems is continu- ously increased with time and learning curve. The potential dependent adsorption of iodine adsorbed on nobel metal Au(111) surfaces is studied in acidic solution. Further stability measurements in acidic solution include two-dimensional hexagonal boron nitride grown on Rh(111) and wide-band gap semiconductor oxide TiO2(110). Metallic iron oxide magnetite Fe3O4 single crystal surfaces (001) and (111) are shown to be stable from neutral to alkaline solutions. Based on this findings, Fe3O4(001) doped with Ni is used as a model system for the oxygen evolution reaction (OER) in alkaline media.Tungsten dissolution and subsequent hydrated tungsten oxide adsorption is stud- ied on all of the studied single crystal surfaces and alternatives for the use of tungsten tips are presented, including PtIr alloys and pure Ir as tip material. (author)