Sulfate and CO surface complexes formation with upd copper on Pd(111) and Pt(111) electrode surfaces: abnormal vibrational frequency shifts of CO and sulfate during upd processes

Abstract

Carbon monoxide (CO) and sulfuric acid anion contacted with underpotential deposition (upd) copper on Pd(111) and Pt(111) electrode surfaces in 0.5 M H 2SO 4 solution were studied by cyclic voltammetry (CV) and in situ infrared reflection absorption spectroscopy (IRAS). CO was stabilized on copper covered Pd(111) and Pt(111) electrode surfaces. Both CO and (bi)sulfate molecules that were stabilized with copper, showed no potential dependent frequency shift in band center position over a certain potential range. Copper (bi)sulfate or copper carbonyl surface metal complexes are formed on Pd(111) and Pt(111) electrode surfaces in the potential range. The copper atoms in the upd potential range on Pd(111) or Pt(111) electrode do not form an ordinal metal ds band structure, but exhibit insulator like characteristics, due to excess positive charge of copper and ionic pseudo-copper metal complex formation on the surface.