Elementary steps in the oxidation and dissociative chemisorption of ethanol on smooth and stepped surface planes of platinum electrodes

Infrared spectroscopy is applied to map pathways in the electrocatalytic oxidation of ethanol at platinum electrodes. Reactions at Pt(111), Pt(335) and polycrystalline platinum are studied for ethanol at 1-4 mM in 0.1 M HClO₄. Isotopic labelling is used to track the fate of carbon atoms on the alcohol and methyl groups across a range of potentials from the hydrogen adsorption region to the leading edge of the oxide region. For the C-C bond cleavage pathway, routes to the stable adsorbed carbon monoxide intermediate depend upon the applied potential. In the hydrogen adsorption region, adsorbed CO originating from the carbon on the alcohol group is detected, while more positive potentials are required to oxidize the methyl group. For the direct oxidation pathway, all surfaces catalyze the four-electron route to acetic acid. Strong vibrational bands from adsorbed acetic acid are detected during ethanol oxidation for the first time, and the appearance of these features correlates with a region of reaction inhibition in the voltammetry. In all cases, reactions progress to a greater extent at the Pt(335) and polycrystalline electrodes.