IN-SITU ELECTROCHEMICAL SCANNING-TUNNELING-MICROSCOPY OF CO(0001) SINGLE-CRYSTAL ELECTRODES IN ACIDIC SOLUTION

The surface of a Co(0001) single crystal electrode was examined by in situ electrochemical scanning tunneling microscopy (STM) in 0.05 M Na2 SO4 at pH 3 under potential control. Cyclic voltammetry indicated that the anodic dissolution of Co proceeds without passivation, and the an odic current was almost proportional to applied potential. The Co(0001 )-(1 X 1) structure was observed on atomically flat terraces in the po tential range between the hydrogen evolution and the onset of the anod ic dissolution. At the foot of the rising anodic current-potential cur ve, a hexagonal surface lattice with (5 X 5) symmetry corresponding cl osely to that of CoO(111) or Co(OH)(2)(0001) was also observed. In the early stages of anodic dissolution, the process proceeded in the laye r-by-layer mode, forming atomically flat terraces extending over large areas. By reapplying a negative potential after the anodic dissolutio n, well-defined terrace-step structures were restored, suggesting that the electrodeposition also took place preferentially at step edges. ( C) 1997 Elsevier Science S.A.