The Underpotential Deposition of Lead and its Effect on Carbon Monoxide Adsorption on Pt(111) Electrode

Abstract

In situ scanning tunneling microscopy (STM) was used to examine the spatial structures of lead (Pb) adatom and carbon monoxide (CO) molecule adsorbed onto an ordered Pt(111) electrode in 0.1 M perchloric acid (HClO4) containing 1 mM Pb(ClO4)2 under potential control. Ordered Pb structures were not seen until the potential was made more negative to 0 V (vs Ag/AgCl), where a quasi-square array (√7 × √57) was seen. Shifting the potential more negative substantiated Pb deposition, which triggered restructuring of the Pb adlayer into (√21 × √21)R11° and (3 × 2√3)rect (θ = 0.62 and 0.67) at −0.1 V. Pb adatom reduced the poisoning effect of CO on the Pt(111) electrode by blocking the adsorption of CO and by forcing CO molecule to asymmetric sites. An ordered (√7 × 3)—Pb + CO structure was imaged at 0 V in 0.1 M HClO4 + 1 mM Pb(ClO4)2, from which the surface coverage and binding sites of CO molecule were inferred.