Electro-optical studies of submonolayers of lead formed on gold electrodes by faradaic adsorption in 1 M HClO4

Current-potential and specular reflectivity-potential curves of a Au electrode have been measured in 1 M CHlO₄ in the presence of 1·0 × 10^?3 M Pb²⁺. Four peaks were found on a linear sweep voltammogram at potentials more positive than the Nernst reversible potential of Pb⁰/Pb²⁺ couple, which are attributed to the Faradaic adsorption of Pb²⁺.

Specular reflectivity-potential curves recorded simultaneously at varied wavelengths gave a clear indication of the adsorption which increased the reflectivity at shorter wavelengths while decreased at longer wavelengths.

From the analysis of the current-potential curve of four peaks in relation to the reflectivity change, the following results were obtained:

(1) The existence of four peaks on the voltammogram is the indication of four different adsorbed states.

(2) The Pb atoms in a submonolayer on Au electrode have rather similar optical properties to those of metallic Pb except for the adsorbed atoms formed at the most potential region.

(3) The adsorbed Pb formed at the most positive potential region have the shortest distance to the surface Au atom, and accordingly, have the strongest interaction with the surface.