IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Electrochemistry and Fluid-Solid Interfaces Monday Sessions
       Session EC-MoP

Paper EC-MoP1
Ex situ and In situ Investigations of Dilute Perchloric Acid on Cu(111)

Monday, October 29, 2001, 5:30 pm, Room 134/135

Session: Poster Session
Presenter: M. Duisberg, University of Bonn, Germany
Authors: M. Duisberg, University of Bonn, Germany
P. Wahl, University of Bonn, Germany
B. Obliers, University of Bonn, Germany
J. Hommrich, University of Bonn, Germany
P. Broekmann, University of Bonn, Germany
K. Wandelt, University of Bonn, Germany
Correspondent: Click to Email
In electrochemistry perchloric acid is assumed to be a prototype for an inert electrolyte. This statement, however, turns out to be not correct for copper electrode surfaces. In this study we present combined in-situ and ex-situ mesurements illustrating the surface electrochemistry of a Cu(111) electrode exposed to a dilute perchloric acid electrolyte. The initial cyclic voltammogram (CV) of an UHV prepared Cu(111) single crystal in 10 mM HClO@sub 4@ shows a reversible pair of peaks at 180 mV vs RHE. After a few cycles this CV changes into a CV identical to that directly obtained after an electropolishing preparation procedure which does not show this reversible pair of peaks. Additional to this fast change there is a long time instability of the CV. A prolonged cycling of the potential leads to the formation of a cathodic peak at -220 mV and a smaller anodic peak at 190 mV. Additionally the onset of hydrogen evolution is shifted towards cathodic potentials by 60 mV in comparison to the initial CV. In-situ STM measurements of Cu(111) in perchloric acid reveal a completely disordered adlayer which is present at anodic electrode potentials. The bare copper surface is not seen under these conditions as one would expect for an inert electrolyte. Ex-situ XPS and LEIS measurements indicate the presence of copper oxide species and chloride as well. The origin of this species at the surface will be discussed. At cathodic potentials near the onset of hydrogen evolution a highly ordered superstructure is observed by STM. This adlayer remains stable also under massive hydrogen evolution. Under similar conditions identical adlayers were also found in other acidic elctrolytes like sulfuric acid or hydrobromic acid, and are attributed to ordered hydronium/water layers.