ELECTROOXIDATION OF ETHYLENE-GLYCOL ON BISMUTH-MODIFIED PT(111)

The influence of predosed bismuth upon the electrooxidation kinetics and pathways of ethylene glycol on Pt(111) in 0.1 mol dm -3 HClO4, has been examined by means of voltammetry combined with real-time infrared spectroscopy. On both unmodified and bismuth-modified Pt(111), two major oxidation products, oxalic acid and CO2, are formed via distinct reaction pathways. The presence of predosed bismuth adatoms significantly alters the selectivity of the electrocatalyst in that the production of CO2 increases monotonically with the bismuth coverage at the expense of the oxalic acid yield. The formation of CO2 was also observed starting from oxalic acid and other partial oxidation products, yet bismuth exerts little effect on the reaction kinetics in these cases. Adsorbed CO was also seen to be produced at positive potentials prior to, and during, the electrooxidation of ethylene glycol and especially from aldehyde-containing partially oxidized species. While the presence of predosed bismuth efficiently eliminates adsorbed CO formation from ethylene glycol, it has little effect for the aldehyde reactants. Significantly and surprisingly, the results suggest that ensembles of contiguous active sites are required for the partial oxidation of ethylene glycol to form oxalic acid but not for the exhaustive electrooxidation pathway yielding CO2.