ELECTROCHEMICAL-BEHAVIOR OF OXOCARBONS ON SINGLE-CRYSTAL PLATINUM-ELECTRODES .3. CROCONIC ACID OXIDATION ON PT(111) SURFACES IN ACID-MEDIUM

The electrochemical behaviour of croconic acid (CRA) on Pt(111) electr odes has been studied in acid medium by cyclic voltammetry. Its oxidat ion proceeds via a dual path mechanism. The direct oxidation path take s place at potentials higher than 0.9 V, probably involving incipient surface oxide formation. The formation of strongly adsorbed species up on CRA adsorption is influenced by the concentration of CRA and the ad sorption potential. At open circuit, only COads is formed, while at co ntrolled potentials lower than 0.40 V, other adsorbates, probably with more than one carbon atom, exist. These are oxidized to CO in the ran ge 0.4-0.6 V. ?he activity for poison formation at open circuit is muc h lower for concentrations higher than 1 mM. FTIR experiments clearly indicate that carbon monoxide is not formed at potentials lower than 0 .40 V. Linearly- and bridge-bonded CO adspecies appear at potentials h igher than 0.40 V, which are oxidized to CO2 before the direct oxidati on of CRA begins. A band at 1780 cm(-1) indicates the presence of leuc onic acid at potentials between 0.95 and 1.22 V as a product of the la tter process, At higher potentials, CRA is completely oxidized to CO2.