STRUCTURE AND REACTIVITY OF BIMETALLIC ELECTROCHEMICAL INTERFACES - INFRARED SPECTROSCOPIC STUDIES OF CARBON-MONOXIDE ADSORPTION AND FORMIC-ACID ELECTROOXIDATION ON ANTIMONY-MODIFIED PT(100) AND PT(111)

The influence of predosed antimony on the adlayer structures of carbon monoxide and on the electro-oxidation kinetics of formic acid on Pt(1 00) and Pt(111) in 0.1M HClO4 is examined by means of in-situ infrared spectroscopy in conjunction with cyclic voltammetry. Preadsorbed anti mony inhibits the adsorption of CO on these surfaces, the attenuation in CO coverage being accompanied by a selective removal of the two-fol d bridging geometry as deduced from the relative nu(CO) band intensiti es. At saturation antimony coverages, the CO binding is exclusively te rminal on Pt(100) and Pt(111). These findings are consistent with the adsorption of antimony at multi-fold sites, yielding microscopically i ntermixed adlayers with CO. The electro-oxidation rates of formic acid are enhanced substantially by preadsorbed antimony on Pt(100) and Pt( 111). The real-time infrared spectra in the C-O stretching region and the CO coverages thereby deduced in the presence of predosed antimony under reactive voltammetric conditions suggest that the metal adatoms are actively involved in the dissociation of formic acid. The origins of the enhanced electrocatalytic activity of the bimetallic Sb/Pt surf aces are discussed in terms of geometric and chemical effects.