Study of Ethanol Electrooxidation in Alkaline Electrolytes with Isotope Labels and Sum-Frequency Generation

The ethanol electrooxidation reaction (EOR) on polycrystalline Pt catalysts in alkaline solution was studied for the first time with broadband sum-frequency generation (BB-SFG) spectroscopy. We find that C–C bond cleavage and CO formation occur as early as 0.05 V versus reversible hydrogen electrode (RHE), and that CO is oxidized at ∼0.45 V, which is 0.2 V lower than in acidic media. In order to track the oxidation of single-carbon intermediates, we have monitored the oxidation of isotopically labeled ethanol ( 12 CH 3 13 CH 2 OH). Surface-adsorbed 12 CO and 13 CO are observed and show very different potential-dependent behaviors. 13 CO molecules formed from preoxidized carbon species such as −CH x O, show the behavior expected from studies of CO-saturated alkaline media. 12 CO, however, which is indicative of the oxidation of methyl-like species (−CH x ) on the catalyst surface, is observed at unusually high potentials. The strongly adsorbed −CH x is not oxidatively removed from the surface until the electrode potential is swept past 0.65 V.