AN ELECTROCHEMICAL AND UV-VISIBLE POTENTIAL-MODULATED REFLECTANCE STUDY OF THE ELECTROOXIDATION OF CARBON-MONOXIDE ON OXIDE-FREE SMOOTH PLATINUM .1. RESULTS IN 0.5 M HCLO4

The electrooxidation of CO on oxide-free smooth Pt in 0.5 M HClO4 has been studied by steady-state and linear potential sweep techniques, and adsorbed species have been identified by UV-vis Potential-Modulated Reflectance Spectroscopy (PMRS). The potential at which CO was first admitted to the electrolyte (E(adm)) influenced dramatically the electrocatalytic ability of Pt to electrooxidise dissolved CO, as first reported by Kita et al. Diffusion-limited oxidation of CO at + 0.47 V vs. RHE was achieved for E(adm) less-than-or-equal-to +0.1 V. The activity for dissolved CO electrooxidation was nearly independent of the direction of the potential sweep prior to reaching E(adm), and of aging of the electrode in nitrogen gas at E(adm) prior to CO admission. The voltammetric peaks of both non-poisoning and poisoning chemisorbed CO species could be observed even in CO-saturated solution. The concentrations of these chemisorbed CO species depended mainly on E(adm), but also on the direction from which E(adm) was reached, up to E(adm) = +0.22 V. The PMR spectrum of chemisorbed CO shows a maximum at 272 nm, which has been assigned to chemisorbed CO probably in the linear form. Reflectograms at the wavelength of the PMRS maximum taken during a slow linear potential sweep have confirmed that the maximum was due to chemisorbed CO.