Early Stages during the Oxidation of HCOOH on Single-Crystal Pt Electrodes As Characterized by Infrared Spectroscopy

Spectral data for HCOOH oxidation at Pt(111), Pt(100), and Pt(110) are presented and discussed. Spectra were taken shortly after the surfaces were contacted with a 0.1 M HCOOH/0.1 M HClO 4 solution at a controlled potential of 0.05 V vs RHE and give information on the adsorption and oxidation processes at the early stages. The formation of on top and bridging CO on Pt(111) and Pt(100) is followed as a function of potential. Conversion of bridging into on top CO is observed at the Pt(100) surface in the low-potential region, while the parallel formation of both forms of adsorbed CO occurs at Pt(111) in the 0.1−0.4 V potential range. Only terminal CO is formed at Pt(110), this surface being the one presenting the highest level of poisoning at the initial potential. Very high values of the initial slopes of ν− E plots are observed for Pt(111) and Pt(100), which are rationalized in terms of lateral coupling due to adsorption in patches giving rise to high local coverages.