Underpotential deposition of Cu on Pt(001): Interface structure and the influence of adsorbed bromide

Abstract

Using in situ x-ray diffraction, we studied the underpotential deposition (UPD) of copper onto a Pt(001) electrode both in pure perchloric acid and in the presence of bromide anions. In pure perchloric acid, the Cu is deposited in pseudomorphic $p(1\ifmmode\times\else\texttimes\fi{}1)$ islands. In the presence of bromide anions, the strong Pt-Br interaction significantly broadens the potential range of Cu UPD. We propose that Br remains in the interface region throughout the UPD process, at first in a disordered Cu-Br phase and then, at more negative potential, forming a $c(2\ifmmode\times\else\texttimes\fi{}2)$ closed-packed monolayer on top of the completed $p(1\ifmmode\times\else\texttimes\fi{}1)$ Cu monolayer. The structures are compared to those found during Cu UPD onto Pt(111), and explained in terms of the metal-halide interactions and the Pt surface atomic geometry.