Coadsorption of anions and water molecule during underpotential deposition of Cu and Pb on the Au (1 1 1) electrode surface

Coadsorption of water and anions and IR background shift were observed during the underpotential deposition of Cu on Au (1 1 1) in H2SO4 and in HClO4 solutions using attenuated total reflection-infrared spectroscopy. Phase transition of the deposited Cu structures was confirmed by significant frequency shift of the n(S–O) mode from SO42−. Delayed ordering of water to SO42− was found. Only IR background shift was observed for the Pb-UPD process due to an inherently weak interation between Pb and anions. It was rationalized by the effective medium theory assuming a slight change in dielectric constant of the absorbate layer upon chemisorption.