Binding Energy Shifts for Cu and Ag UPD on Rh(111) Determined by Online EC-XPS

The nature of Cu and Ag underpotentially-deposited on Rh(111) was investigated by X-ray photoelectron spectroscopy (XPS). These underpotential deposition (UPD) systems present multipeak features, which were evaluated by cyclic voltammetry and in terms of binding energy shifts. The use of different electrolytes (sulfuric and perchloric acid) strongly affected the metallic coverage and slightly affected the UPD shifts. Through XPS, the examined surfaces were found to contain C, O, and S or Cl, which confirms the presence of anions and/or products of their reduction at the Rh(111) surface, in addition to the deposited metals. The binding energies for underpotentially-deposited Cu and Ag displayed negative shifts (to lower binding energy) with respect to both the bulk deposits and clean metal references. These negative shifts were discussed in terms of contributions from charge transfer, orbital rehybridization, and lattice strain.