Scanning Tunneling Microscopic Study with Atomic Resolution of the Dissolution of Cu(100) Electrodes in Aqueous Chloride Media

In situ scanning tunneling microscopy (STM) of the dissolution of a Cu(100) electrode in aqueous chloride media (HC1) was employed to find the mechanism of reaction at the atomic level. Imaging the surface at potentials where no dissolution occurred resulted in a clear ( 4 2 x 42)R45' C1 structure with an observed C1-C1 distance of 0.35 f 0.02 nm, in agreement with previous ultrahigh vaccum surface analytical lowenergy electron diffraction and Auger electron analysis studies of Cu(100) surfaces dosed with chlorine or aqueous C1-. Images acquired at potentials where dissolution was modest showed the preferred reaction sites were step edges with edges always retreating along the Cu(100) ( 100) direction. At still higher potentials, the rate increased and the reaction sites were still mainly the step edges. This work compares well with a previous STM study of Cu(ll1) electrodes under similar conditions, where the dissolution of the Cu( 11 1) caused reaction along (21 l} step edges, which are very similar to the Cu(100) { 100) step edges.