Atomic structures of a Cu(111) surface under electrochemical conditions:: An in-situ STM study

The atomic structures of a Cu(111) electrode in dilute sulfuric electrolyte have been studied using in-situ STM. At anodic potentials near the copper dissolution the adsorbed sulfate anions form a characteristic anisotropic Moire pattern. The appearance of the long range Moire modulation is explained by a sulfate-induced reconstruction (expansion) of the topmost copper layer and the resulting misfit between the first and the second copper layer. For the first time it was possible to image not only the sulfate adsorbate but also the underlying reconstructed copper substrate at the same anodic working potential by a systematical variation of the tunneling parameters. On an atomic scale the observed sulfate structure on Cu(111) is very similar to those found for other fcc(111) surfaces (Au, Pt and Rh). On these electrodes sulfate anions form a regular (root 3 x root 7) superstructure. For the Cu(111) surface a (root 3 x root 7)-like unit cell is found which is slightly distorted. Also for the first time it was possible to image the atomic structure of an electrode during a massive hydrogen evolution current at cathodic potentials. Even under such extreme electrochemical conditions far from the thermodynamic equilibrium an ordered superstructure bf hydronium cations is found. At the anodic end of the cyclic voltammogram a pit-etching mechanism is induced by a fast copper corrosion.