520 Surface Science 175 (1986) 520-534 North-Holland. Amsterdam zyxwvutsrqp ELECTRODEPOSITION OF Pb ONTO Pt(ll1) IN AQUEOUS CHLORIDE SOLUTIONS Studies by LEED and Auger spectroscopy Bruce C. SCHARDT, John L. STICKNEY *, Donald A. STERN, Andrzej WIECKOWSKI **, Donald C. ZAPIEN and Arthur T. HUBBARD*** Received 11 December 1985; accepted for publication 6 May 19X6 Studies by LEED and Auger spectroscopy of Pb electrodeposited from aqueous WC1 solutions onto well-defined Pt(lll) surfaces are reported. Adsorption of HCI from pure aqueous HCI solutions (pH = 0 to 4) onto Pt(ll1) at electrode potentials from 0.4 to 0.X volt (versus AgCl reference electrode) resulted III a stable (3 x 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 Pb2+ tons were present in the chloride solution, spontaneous (open circuit) electrodeposition of Pb occurred (B ,,,, = 0.05), altering the sizes. shapes. and intensities of beams in the (3 x 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 obtalned 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 8 r,h = I. 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. 1. Introduction In previous articles we reported studies by LEED and Auger spectroscopy of Ag and Cu electrodeposited onto well-defined Pt(lll), Pt( loo), and Pt(s)(6(111) X (111)) surfaces pretreated with I1 vapor. Each stage of the electrodeposition process was sensitive to the structure of the electrode surface and of the layer of adsorbed electrolyte. Highly ordered layers of deposited metal and adsorbate were formed in most cases [l-7]. * Present address: Department of Chemistry. University of Georgia. Athens, GA 30602. USA. ** Present address: Department of Chemistry. University of Illinois. Urbana. IL 61X01. USA. *** To whom correspondence should he addressed. 0039-6028/86/$03.50 Q Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)