Donald C. Zapien

Electrodeposition of Pb onto Pt(111) in aqueous chloride solutions : Studies by LEED and Auger spectroscopy

Abstract Studies by LEED and Auger spectroscopy of Pb electrodeposited from aqueous HCl solutions onto well-defined Pt(111) surfaces are reported. Adsorption of HCl from pure aqueous HCl solutions ( pH = 0 to 4) onto Pt(111) at electrode potentials from 0.4 to 0.8 volt (versus AgCl reference electrode) resulted in a stable (3×3) adlattice; however, below 0.4 volt adsorption was weak and desorption occurred readily under the influence of the electron beams employed for LEED or Auger spectroscopy. When Pb 2+ ions were present in the chloride solution, spontaneous (open circuit) electrodeposition of Pb occurred ( θ Pb = 0.05), altering the sizes, shapes, and intensities of beams in the (3×3) pattern. Electrodeposition of Pb under conditions of negative linear potential scan resulted in a series of ten peaks at potentials more positive than the peak for deposition of bulk Pb. LEED patterns obtained after emersion of the surface at various stages during the scan revealed that the electrodeposited layer was ordered and underwent a series of structural transitions with increasing Pb coverage. Comparison of the Auger signal for Pb with the coulometric charge for Pb deposition demonstrated that the Pb deposit was not stable at open circuit (as in emersion) when the packing density exceeded about θ Pb = 1. The Auger signal for Cl was not generally attenuated by deposition of Pb. indicating that Cl was present in the topmost layer of the surface at all Pb coverages.

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

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, θI = 37 = 0.43, formed in HI + HBr mixtures; and Pt (111)(3×3)−I, containing θI = 49 = 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.