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)

Abstract

The influence of predosed antimony on the adlayer structures of carbon monoxide and on the electro-oxidation kinetics of formic acid on Pt(100) and Pt(111) in 0.1M HClO 4 is examined by means of in-situ infrared spectroscopy in conjunction with cyclic voltammetry. Preadsorbed antimony inhibits the adsorption of CO on these surfaces, the attenuation in CO coverage being accompanied by a selective removal of the two-fold bridging geometry as deduced from the relative ν CO band intensities. At saturation antimony coverages, the CO binding is exclusively terminal on Pt(100) and Pt(111). These findings are consistent with the adsorption of antimony at multi-fold sites, yielding microscopically intermixed 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 surfaces are discussed in terms of geometric and chemical effects.