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.