INSITU SPECTROSCOPIC STUDY OF THE ADSORPTION OF CARBON-MONOXIDE ON A POLYCRYSTALLINE RUTHENIUM ELECTRODE BY EMIRS AND PMRS

The adsorption of CO on polycrystalline ruthenium was studied by cyclic voltammetry and by in-situ infrared (EMIRS) and UV-visible (PMRS = potential-modulated reflectance spectroscopy) techniques both in 0.5 M HClO4 and in 1 M NaOH. Hydrogen adsorption was blocked by chemisorbed CO in both media, as is usually observed. Steady-state currents of CO electro-oxidation were observed in acid but not in alkaline media. The lack of electrocatalytic activity in base was not due to poisoning by a chemisorbed species, but was attributed to the presence on the surface of an inactive ruthenium oxide. An EMIRS bipolar band was seen in CO-saturated solution at 2040 cm-1 in acid and at 1970 cm-1 in base. It was due to the stretching vibration of CO chemisorbed on Ru, in the linear and bridged form, respectively. Similarly, a PMRS maximum was observed at a wavelength of 265 nm in acid and 285 nm in base, which were also attributed to linear and bridged CO, respectively. At the wavelength of the maximum, the PMRS signal intensity increased linearly with the modulation amplitude, and changed little with the modulation frequency, which shows that the PMRS signal is an electric field effect.