Berlin 2008 – wissenschaftliches Programm
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O: Fachverband Oberflächenphysik
O 32: Oxides and Insulators: Clean Surfaces
O 32.14: Vortrag
Dienstag, 26. Februar 2008, 16:15–16:30, MA 042
STM of superstructures and surface transformations on Pt(111) in a sulfuric acid electrolyte — •Björn Braunschweig and Winfried Daum — Institut für Physik und Physikalische Technologien, TU-Clausthal, Leibnizstrasse 4, D-38678 Clausthal-Zellerfeld
Imaging of weakly chemisorbed species on Pt surfaces with the STM in electrochemical environments and with molecular resolution is a challenge to the experimenter as these electrode surfaces are very susceptible to contaminations at a level well below the sensitivity of cyclic voltammetry. We have investigated the surface structure of Pt(111) in a 0.1 M H2SO4 electrolyte in the potential range of sulfate adsorption. In agreement with a previous study [1] we observe a disorder-order transitions at a potential of 0.5 V versus the reversible hydrogen electrode (RHE). For potentials between 0.5 and 0.8 V RHE we identified two distinctly different sulfate superstructures: the well-known (√3×√7)R19.1∘ superstructure and a new (3x1) superstructure. We were able to simultaneously image the sulfate and the Pt surface lattice and to determine the registry of the sulfate anions with the substrate. The structure in the unit cell of the (3x1) superstructure indicates the presence of an additional molecular component, possibly hydronium or water molecules. For potential sweeps to 0.8 V RHE and above the ordered sulfate overlayer changes instantaneously to a more disordered structure presumably due to adsorption of OH− ions.
[1] A.M. Funtikov, U. Linke, U. Stimming and R. Vogel; Surf.Sci. 324, L343 (1995) and J. Electroanal. Chem. 428, 147 (1997)