Electrodeposition of Pb onto Pt (111) surfaces containing iodine adlattices: Studies by low-energy electron diffraction and Auger spectroscopy

Abstract

Studies of low-energy electron diffraction (LEED) and Auger spectroscopy of Pb electrodeposited from aqueous HI or HBr + HI mixtures onto well-characterized Pt (111) surfaces are reported. I − was strongly absorbed at Pt (111) to form an ordered adsorbed layer, an adlattice. The effect of electrolyte and adlattice structure on the electrodeposition behavior of Pb was investigated for two distinct adlattices: Pt (111)(√7 × √7)R19° − I, containing three I atoms per seven surface Pt atoms, θ I = 3 7 = 0.43, formed in HI + HBr mixtures; and Pt (111)(3×3)−I, containing θ I = 4 9 = 0.44, formed in pure HI. The Auger signal for I was not strongly attenuated by Pb deposition, indicating that I atoms were present in the topmost layer of the surface at all Pb coverages. Electrodeposition proceeded differently in the two cases: deposition from the HBr + HI mixture occurred in three narrow underpotential regions to form three highly ordered new structures. Depositioin from pure HI spanned a broad range of underpotentials followed by one prominent, narrow underpotential feature to form structures having limited stability toward emersion.