In Situ Infrared Study of the Electrooxidation of Ethanol and Acetaldehyde in Acid Electrolyte

Abstract The electrooxidation of ethanol and acetaldehyde on Pt/C has been studied by using in situ IR spectroscopy. To identify the species formed during the electrooxidation reactions accurately, the IR spectra were collected in both HClO 4 /H 2 O and HClO 4 /D 2 O electrolytes. The results shown herein reveal that ethanol adsorbs on Pt at low potentials in a series of dehydrogenative steps that lead to η 2 ‐acetaldehyde prior to the scission of the C−C bond, which takes place at potentials higher than 150 mV. At potentials of approximately 220 mV, the Pt surface is fully covered by CO ad (and C 1,ad ) species, which thus impede further ethanol adsorption. At higher potentials, when OH ad species are nucleated, CO ad is oxidized to CO 2 , which releases Pt sites for further ethanol adsorption and oxidation. However, due to the presence of OH ad species, ethanol oxidation to acetic acid is the preferred reaction pathway. In contrast, the C−C bond of acetaldehyde is broken at 50 mV, which leads to the formation of a full monolayer of CO and CH x adsorbed species on Pt. The IR spectra collected in an electrolyte that contained D 2 O show no evidence for the formation of acetyl species prior to the scission of the C−C bond.