The effect of halides on the structure of copper underpotential-deposited onto Pt(111): a low-energy electron diffraction and X-ray photoelectron spectroscopy study

Abstract

The influence of chloride and bromide ions on the underpotential deposition of copper onto Pt(111) in sulphuric acid solutions was studied ex situ by low-energy electron diffraction (LEED) and X-ray photoelectron spectroscope (XPS). It is demonstrated that the growth behaviour of the copper monolayer is drastically altered when Cl − or Br − is added to the electrolyte. The halides form densely packed, incommensurate (4 × 4) and (7 × 7) structures respectively, on the full copper monolayer (which itself is in registry with the substrate) before they arrange themselves in a more open structure at more negative potentials. Furthermore, it is shown that both halides have a marked influence on the cyclic voltammogram of underpotential deposited copper, which renders a reliable evaluation of the copper coverage from charge measurements impossible. The correct isotherm for copper on Pt(111) in the presence of Cl − is evaluated from XPS data.