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 ( ¹²CH₃¹³CH₂OH). Surface-adsorbed ¹²CO and ¹³CO are observed and show very different potential-dependent behaviors. ¹³CO molecules formed from preoxidized carbon species such as -CH_xO, show the behavior expected from studies of CO-saturated alkaline media. ¹²CO, 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.