Surface chemistry of electrodes: Cu(111) in aqueous HCl

Fundamental studies of the surface chemistry of copper electrodes have been performed. The composition and structure present at a six-sided Cu(111) electrode emersed (removed) from a 1mM HCl solution have been investigated with low-energy electron diffraction (LEED) and Auger spectroscopy. Experiments were performed in an UHV surface analysis instrument directly coupled to an antechamber containing a standard electrochemical cell. Electrode surface composition was examined as a function of emersion potential and the extent of oxidation and Cu deposition. A Cu(111) (√3×√3)R30°-split-Cl pattern was observed and was relatively unchanged under a variety of voltammetric programs and emersion potentials. The LEED pattern indicated a large surface unit cell. A proposed structure with a unit cell defined by phase boundaries and a local (√3×√3)R30° symmetry within the unit cell has been proposed. Electrochemical potential programs such as the dissolution and deposition of copper did not result either in the degradation of the LEED pattern or in significant changes in the Cl/Cu Auger ratio, indicating ordered stoichiometric deposition of copper. Rinsing of the copper chloride surface with water also resulted in no detectable changes in composition or structure.