VOLTAMMETRIC AND SUBTRACTIVELY NORMALIZED INTERFACIAL FTIR STUDY OF THE ADSORPTION AND OXIDATION OF L(+)-ASCORBIC ACID ON PT ELECTRODES IN ACID-MEDIUM - EFFECT OF BI ADATOMS

The adsorption and oxidation of L(+)-ascorbic acid on bare and Bi-covered Pt electrodes in a sulfuric acid medium have been studied by cyclic voltammetry and in situ FTIR spectroscopy. The latter technique has allowed the direct detection of CO(ads) from ascorbic acid adsorption, both at open-circuit and controlled potential, for the bare Pt surface. Under these latter conditions both linearly bonded and multi-bonded CO were detected. The existence of other strongly adsorbed species which are oxidized in the oxygen adsorption region has been demonstrated by cyclic voltammetry. The formation of all these adsorbed species is completely suppressed on the Bi-covered Pt surface under UPD conditions. Ascorbic acid oxidation was monitored by following the variation of the IR spectra in the presence and in the absence of Bi3+ in solution. The electrocatalytic effect of the Bi adlayer can be explained mainly through the suppression of any dissociative adsorption step leading to the formation of strongly adsorbed species.