Underpotential and bulk deposition of copper on Pd(111) in sulfuric acid solution studied by in situ scanning tunneling microscopy

The underpotential deposition (UPD) of Cu was investigated on a Pd(111) electrode in a H2SO4 solution by using voltammetry and in situ scanning tunneling microscopy (STM). The UPD of Cu yielded a single current peak on Pd(111) in H2SO4 to form a (1 × 1) monolayer. The so-called (√3 × √7) structure of sulfate/bisulfate was consistently observed at potentials negative and positive with respect to the UPD peak. Both the packing arrangement of (√3 × √7) and the internal structure of sulfate/bisulfate were imaged by STM. Bulk deposition of Cu proceeded epitaxially. On the atomically flat surface of the Cu layer, a Moiré pattern was observed.