In Situ, Time-Resolved Reflectance Spectroscopy in the Microsecond Domain:  Oxidation of Adsorbed Carbon Monoxide on Polycrystalline Pt Microelectrodes in Aqueous Solutions^†

The dynamics of the electrooxidation of adsorbed CO, CO_ads, on polycrystalline Pt microelectrodes has been examined in CO-saturated 0.5 M H₂SO₄ and 0.5 M HClO₄ aqueous solutions, using in situ, time-resolved, normalized differential reflectance spectroscopy (λ = 633 nm). Attention was focused on the unique dependence of CO_ads oxidation on the potential at which the adsorbed full CO monolayer is assembled (i.e., hydrogen adsorption/desorption vs the double-layer region) using both fast linear scan voltammetry and potential step techniques. As evidenced from the data collected, CO_ads oxidation at a fixed potential proceeds at slower rates when the monolayer is formed in the double- layer region compared to when it is formed in the hydrogen adsorption/desorption region. Possible explanations for this effect are discussed.